Here below some MCQ with answer of inheritance chapter. Which is explained in details. Let’s check one by one.
- Which of the following is an example of incomplete dominance?
a) Blood group inheritance in humans
b) Flower color in Mirabilis jalapa
c) Skin color in humans
d) Eye color inheritance in humans
Answer: (b) Flower color in Mirabilis jalapa
Explanation: In incomplete dominance, the heterozygous offspring shows a phenotype that is an intermediate of the two homozygous parents. In Mirabilis jalapa (Four O’clock plant), when a red-flowered plant (RR) is crossed with a white-flowered plant (rr), the offspring (Rr) have pink flowers. Neither the red nor the white allele is completely dominant over the other.
- Which of the following conditions is not a part of Mendel’s law of segregation?
a) Each individual possesses two alleles for each trait
b) Alleles segregate during gamete formation
c) Alleles blend together in the offspring
d) Gametes receive only one allele for each trait
Answer: (c) Alleles blend together in the offspring
Explanation: According to Mendel’s law of segregation, alleles separate or segregate during gamete formation, and each gamete receives only one allele for each trait. This law contradicts the blending inheritance theory, where it was once believed that traits blend in offspring. Mendel showed that alleles remain distinct and do not blend.
- What is the phenotypic ratio in a dihybrid cross when both traits exhibit complete dominance?
a) 9:3:3:1
b) 1:2:1
c) 3:1
d) 1:1:1:1
Answer: (a) 9:3:3:1
Explanation: In a dihybrid cross (crossing two individuals that are heterozygous for two traits), the phenotypic ratio observed is 9:3:3:1. This occurs when both traits exhibit complete dominance. For example, in a cross between two pea plants heterozygous for seed color (yellow dominant over green) and seed shape (round dominant over wrinkled), the ratio of phenotypes in the offspring would be 9 yellow round: 3 yellow wrinkled: 3 green round: 1 green wrinkled.
- A man with blood group A marries a woman with blood group B. They have a child with blood group O. What are the possible genotypes of the parents?
a) IAIA and IBIB
b) IAi and IBi
c) IAIA and IBi
d) IAi and IBIB
Answer: (b) IAi and IBi
Explanation: Blood group O is only possible if both parents carry the recessive “i” allele. Therefore, the parents must have the genotypes IAi (father) and IBi (mother). This combination allows for the possibility of their child inheriting the “i” allele from both parents, resulting in blood group O.
- Which of the following disorders is an example of sex-linked inheritance?
a) Down syndrome
b) Sickle cell anemia
c) Hemophilia
d) Cystic fibrosis
Answer: (c) Hemophilia
Explanation: Hemophilia is a sex-linked recessive disorder, meaning it is carried on the X chromosome. Since males have only one X chromosome (XY), they are more likely to express the disorder if they inherit the affected X chromosome. Females (XX) are usually carriers unless they inherit the mutated gene on both X chromosomes. The other conditions mentioned are autosomal disorders.
- What is the cause of variation in offspring according to Mendel’s principles?
a) Random fusion of gametes
b) Mutations
c) Law of independent assortment
d) Environmental factors
Answer: (c) Law of independent assortment
Explanation: Mendel’s law of independent assortment states that genes for different traits assort independently of one another during gamete formation. This means that the allele a gamete receives for one trait does not affect the allele received for another trait, leading to variation in the offspring. Although random fusion of gametes and mutations also contribute to genetic variation, Mendel’s principle specifically refers to independent assortment as the cause of variation.
- Which of the following statements is true regarding a test cross?
a) It is performed to determine the genotype of a dominant individual.
b) It is a cross between two heterozygous individuals.
c) It is performed to determine the phenotype of an organism.
d) It is performed between two recessive individuals.
Answer: (a) It is performed to determine the genotype of a dominant individual.
Explanation: A test cross is a cross between an individual showing a dominant phenotype (but with an unknown genotype) and a homozygous recessive individual. It helps determine whether the dominant individual is homozygous (pure) or heterozygous for that trait. If any offspring show the recessive trait, the dominant individual must be heterozygous.
- In a test cross involving F1 dihybrid flies, more parental-type offspring were produced than recombinant-type offspring. This indicates that the genes are:
a) On different chromosomes
b) Linked and far apart
c) Linked and close together
d) Unlinked and assort independently
Answer: (c) Linked and close together
Explanation: When genes are located close together on the same chromosome, they tend to be inherited together, which results in more parental-type offspring than recombinant-type. This phenomenon is known as gene linkage. If genes were far apart or on different chromosomes, there would be more recombination, leading to a higher frequency of recombinant offspring.
- The phenomenon where a single gene influences multiple traits is called:
a) Codominance
b) Epistasis
c) Pleiotropy
d) Polygenic inheritance
Answer: (c) Pleiotropy
Explanation: Pleiotropy occurs when a single gene affects multiple phenotypic traits. For example, the gene responsible for sickle-cell anemia affects the shape of red blood cells, as well as the oxygen-carrying capacity, resistance to malaria, and can cause various health complications. In contrast, polygenic inheritance involves multiple genes affecting a single trait.
- Which of the following traits in humans is an example of polygenic inheritance?
a) Blood group
b) Height
c) Earlobe shape
d) Tongue rolling ability
Answer: (b) Height
Explanation: Polygenic inheritance occurs when multiple genes influence a single trait. Height in humans is controlled by the interaction of several genes, making it a polygenic trait. Traits like blood group and tongue rolling ability are examples of single-gene traits, while earlobe shape may have a more complex inheritance but is not an example of polygenic inheritance.
- Which of the following correctly describes codominance?
a) Both alleles express a blended phenotype
b) One allele completely masks the other
c) Both alleles are equally expressed in the phenotype
d) Neither allele is expressed in the phenotype
Answer: (c) Both alleles are equally expressed in the phenotype
Explanation: In codominance, both alleles contribute equally and independently to the phenotype of the organism. A common example is the AB blood group in humans, where both IA and IB alleles are expressed, resulting in both A and B antigens being present on the surface of red blood cells.
- If a woman with blood group AB marries a man with blood group O, what are the possible blood groups of their offspring?
a) A, B, AB, O
b) A, B
c) AB, O
d) Only O
Answer: (b) A, B
Explanation: The woman with blood group AB has the genotype IAIB, and the man with blood group O has the genotype ii. When crossed, the possible combinations of alleles in their offspring are IAi and IBi, meaning the children could either have blood group A (IAi) or blood group B (IBi). Blood groups AB and O are not possible.
- In a cross between a homozygous tall pea plant (TT) and a homozygous dwarf pea plant (tt), all offspring are tall. This is an example of:
a) Codominance
b) Incomplete dominance
c) Complete dominance
d) Pleiotropy
Answer: (c) Complete dominance
Explanation: Complete dominance occurs when one allele (in this case, T for tallness) completely masks the expression of the other allele (t for dwarfness). The heterozygous offspring (Tt) will exhibit the dominant phenotype, which is tall in this case.
- In a certain plant, yellow flowers (Y) are dominant over white flowers (y), and round seeds (R) are dominant over wrinkled seeds (r). If two plants with the genotype YyRr are crossed, what fraction of the offspring will have yellow flowers and wrinkled seeds?
a) 1/16
b) 3/16
c) 9/16
d) 12/16
Answer: (b) 3/16
Explanation: This is a dihybrid cross where both parents are heterozygous for flower color and seed shape. The phenotypic ratio for the cross will follow a 9:3:3:1 pattern. Of these, 9 will have yellow flowers and round seeds, 3 will have yellow flowers and wrinkled seeds, 3 will have white flowers and round seeds, and 1 will have white flowers and wrinkled seeds. Therefore, 3/16 of the offspring will have yellow flowers and wrinkled seeds.
- In the human ABO blood group system, which blood group is known as the universal recipient?
a) A
b) B
c) AB
d) O
Answer: (c) AB
Explanation: Individuals with blood group AB are called universal recipients because they have both A and B antigens on their red blood cells and no antibodies against A or B in their plasma. This allows them to receive blood from any ABO group without agglutination reactions.
- Which genetic disorder is caused by a recessive allele on an autosome?
a) Huntington’s disease
b) Down syndrome
c) Cystic fibrosis
d) Hemophilia
Answer: (c) Cystic fibrosis
Explanation: Cystic fibrosis is caused by a recessive allele located on an autosome (chromosome 7). An individual must inherit two copies of the faulty allele (one from each parent) to develop the disease. Huntington’s disease is an autosomal dominant disorder, Down syndrome is caused by trisomy 21, and hemophilia is an X-linked recessive disorder.
- Which of the following describes the law of independent assortment?
a) Alleles of a gene segregate from each other during gamete formation
b) Genes located on the same chromosome always assort together
c) Genes for different traits assort independently of each other during gamete formation
d) Homologous chromosomes fail to separate during meiosis
Answer: (c) Genes for different traits assort independently of each other during gamete formation
Explanation: Mendel’s law of independent assortment states that alleles of different genes assort independently during gamete formation, meaning the inheritance of one trait does not influence the inheritance of another. This law applies only when genes are located on different chromosomes or are far apart on the same chromosome.
- A female carrier for color blindness (XcX) marries a normal male (XY). What is the probability that their son will be colorblind?
a) 0%
b) 25%
c) 50%
d) 100%
Answer: (c) 50%
Explanation: Color blindness is an X-linked recessive disorder. The mother is a carrier (XcX), and the father is normal (XY). Sons inherit their X chromosome from their mother and their Y chromosome from their father. There is a 50% chance that a son will inherit the Xc (mutated) chromosome from the mother, making him colorblind.
- Which of the following is an example of a genetic disorder caused by non-disjunction?
a) Sickle cell anemia
b) Hemophilia
c) Down syndrome
d) Cystic fibrosis
Answer: (c) Down syndrome
Explanation: Down syndrome is caused by trisomy 21, which occurs due to non-disjunction, an error during meiosis where homologous chromosomes fail to separate properly. This results in an individual having three copies of chromosome 21 instead of two.
- Which of the following statements is incorrect regarding mutations?
a) Mutations can be beneficial, harmful, or neutral
b) Mutations are the source of new alleles in a population
c) Somatic mutations are heritable and passed on to offspring
d) Mutations can occur spontaneously or due to environmental factors
Answer: (c) Somatic mutations are heritable and passed on to offspring
Explanation: Somatic mutations occur in non-reproductive cells and are not passed on to offspring. Only mutations in germline cells (eggs or sperm) can be inherited. Somatic mutations may affect the individual but do not influence future generations.
- A plant heterozygous for both flower color (Rr) and seed shape (Ss) undergoes self-pollination. What is the probability of obtaining offspring that are homozygous for both traits?
a) 1/16
b) 2/16
c) 4/16
d) 9/16
Answer: (a) 1/16
Explanation: In a dihybrid cross (RrSs x RrSs), the probability of getting offspring that are homozygous for both traits (RRSS, RRss, rrSS, or rrss) is 1/16 for each specific combination. There are four possible homozygous combinations (RRSS, RRss, rrSS, rrss), and each has a probability of 1/16.
- In humans, the gene for red-green color blindness is located on the X chromosome. A man with normal vision marries a woman who is a carrier for the condition. What is the chance that their daughter will be colorblind?
a) 0%
b) 25%
c) 50%
d) 100%
Answer: (a) 0%
Explanation: Since the daughter inherits an X chromosome from both her parents, she would need to inherit two mutated X chromosomes (one from each parent) to be colorblind. Since the father has normal vision (XY), he can only pass a normal X chromosome. Therefore, their daughters cannot be colorblind, though they could be carriers.
- Which of the following patterns of inheritance is characterized by one gene masking the expression of another gene?
a) Pleiotropy
b) Codominance
c) Epistasis
d) Polygenic inheritance
Answer: (c) Epistasis
Explanation: Epistasis occurs when the expression of one gene is affected or completely masked by another gene. An example is coat color in mice, where one gene determines whether pigment is produced, while another gene determines the color of the pigment. If the pigment gene is inactive, the color gene has no effect.
- If two carriers of sickle cell anemia (Ss) have children, what is the probability that their offspring will have sickle cell disease?
a) 0%
b) 25%
c) 50%
d) 75%
Answer: (b) 25%
Explanation: Sickle cell anemia is caused by a recessive allele (s). If both parents are carriers (Ss), there is a 25% chance that the child will inherit two copies of the recessive allele (ss) and thus have the disease, a 50% chance the child will be a carrier (Ss), and a 25% chance the child will be normal (SS).
- Which of the following diseases is caused by a single-gene mutation?
a) Turner syndrome
b) Klinefelter syndrome
c) Huntington’s disease
d) Down syndrome
Answer: (c) Huntington’s disease
Explanation: Huntington’s disease is caused by a mutation in a single gene located on chromosome 4. It is an autosomal dominant disorder, meaning that only one copy of the mutated gene is necessary to cause the disease. The other conditions listed are chromosomal disorders caused by abnormalities in chromosome number, not by single-gene mutations.
- A woman with type A blood (IAIA) marries a man with type B blood (IBIB). What will be the blood type of their offspring?
a) A
b) B
c) AB
d) O
Answer: (c) AB
Explanation: Since the woman is homozygous for blood group A (IAIA) and the man is homozygous for blood group B (IBIB), all of their offspring will inherit one IA allele from the mother and one IB allele from the father, resulting in blood type AB.
- Which of the following is an example of a sex-limited trait?
a) Male-pattern baldness
b) Hemophilia
c) Lactation in females
d) Red-green color blindness
Answer: (c) Lactation in females
Explanation: A sex-limited trait is one that is expressed in only one sex, even though the gene for the trait may be present in both sexes. Lactation is a sex-limited trait because only females produce milk, even though both males and females have the genes for it. Male-pattern baldness is sex-influenced, and hemophilia and color blindness are sex-linked traits.
- What is the probability of producing a homozygous recessive offspring in a cross between two heterozygous individuals (Aa x Aa)?
a) 0%
b) 25%
c) 50%
d) 75%
Answer: (b) 25%
Explanation: In a cross between two heterozygous individuals (Aa x Aa), the offspring can inherit either the dominant allele (A) or the recessive allele (a) from each parent. The genotypic ratio of the offspring is 1:2:1 — one homozygous dominant (AA), two heterozygous (Aa), and one homozygous recessive (aa). Therefore, there is a 25% chance of producing a homozygous recessive offspring (aa).
- In a cross between a red-flowered plant and a white-flowered plant, the F1 generation has pink flowers. This is an example of:
a) Complete dominance
b) Codominance
c) Incomplete dominance
d) Epistasis
Answer: (c) Incomplete dominance
Explanation: In incomplete dominance, the heterozygous phenotype is an intermediate between the two homozygous phenotypes. In this case, the pink flowers in the F1 generation are a result of neither the red nor white alleles being completely dominant, so the resulting phenotype is a blend of the two.
- If a man with blood group AB marries a woman with blood group O, which blood groups are possible in their children?
a) A, B, AB, O
b) A, B, O
c) A, B
d) A, B, AB
Answer: (c) A, B
Explanation: The man has blood group AB (IAIB), and the woman has blood group O (ii). The children will inherit either the IA or IB allele from the father and the i allele from the mother, resulting in either blood group A (IAi) or blood group B (IBi). Blood groups AB and O are not possible in their children.
- A male with Klinefelter syndrome has which of the following chromosomal compositions?
a) 45, X
b) 47, XXY
c) 47, XYY
d) 46, XY
Answer: (b) 47, XXY
Explanation: Klinefelter syndrome is a chromosomal disorder that occurs in males who have an extra X chromosome, resulting in the genotype 47, XXY. This causes a range of symptoms, including reduced fertility and some degree of physical and developmental effects.
- Which of the following statements is true regarding the X-linked recessive trait?
a) Males are more likely to express the trait than females
b) Females with one affected X chromosome will always express the trait
c) Males inherit the trait from their father
d) Both males and females express the trait equally
Answer: (a) Males are more likely to express the trait than females
Explanation: Since males have only one X chromosome, any recessive allele on it will be expressed because there is no second X chromosome to mask it. Females, on the other hand, have two X chromosomes, so they would need two copies of the recessive allele to express the trait. This makes X-linked recessive traits more common in males than in females.
- Which of the following statements is true about a pedigree analysis?
a) Pedigrees can be used to determine whether a trait is dominant or recessive
b) Pedigrees cannot provide information about carriers of a trait
c) Pedigrees are only used to study sex-linked traits
d) Pedigrees do not show family relationships
Answer: (a) Pedigrees can be used to determine whether a trait is dominant or recessive
Explanation: A pedigree is a diagram that shows the inheritance pattern of a trait through several generations of a family. By analyzing the pedigree, one can determine whether a trait is dominant, recessive, autosomal, or sex-linked, and can also identify carriers of recessive traits.
- If a heterozygous tall pea plant (Tt) is crossed with a homozygous short pea plant (tt), what is the expected phenotypic ratio of the offspring?
a) 3 tall: 1 short
b) 1 tall: 1 short
c) 1 tall: 3 short
d) All tall
Answer: (b) 1 tall: 1 short
Explanation: In this monohybrid cross, the heterozygous tall plant (Tt) can pass on either the T (tall) allele or the t (short) allele, while the homozygous short plant (tt) can only pass on the t allele. Therefore, the offspring will be 50% tall (Tt) and 50% short (tt), giving a 1:1 phenotypic ratio.
- Which of the following disorders is caused by trisomy of chromosome 21?
a) Turner syndrome
b) Down syndrome
c) Klinefelter syndrome
d) Edward syndrome
Answer: (b) Down syndrome
Explanation: Down syndrome is caused by trisomy of chromosome 21, meaning that individuals with this condition have three copies of chromosome 21 instead of the normal two. This leads to characteristic physical and developmental traits. Turner syndrome is caused by a missing X chromosome (45, X), Klinefelter syndrome by an extra X chromosome (47, XXY), and Edward syndrome by trisomy of chromosome 18.
- A woman who is a carrier for hemophilia (XHXh) marries a normal man (XHY). What is the probability that their daughter will have hemophilia?
a) 0%
b) 25%
c) 50%
d) 100%
Answer: (a) 0%
Explanation: Hemophilia is an X-linked recessive disorder. Since the father has a normal X chromosome (XHY), the daughter will inherit one normal X chromosome from him and either a normal or carrier X chromosome from the mother. Therefore, daughters cannot have hemophilia, although there is a 50% chance they will be carriers.
- The genetic makeup of an individual is referred to as their:
a) Phenotype
b) Genotype
c) Allele
d) Trait
Answer: (b) Genotype
Explanation: The genotype is the genetic constitution of an individual, representing the combination of alleles they carry for a particular gene or set of genes. The phenotype is the observable characteristics, traits are specific features, and alleles are different forms of a gene.
- Which of the following terms describes the phenomenon where multiple genes influence a single trait?
a) Epistasis
b) Pleiotropy
c) Polygenic inheritance
d) Codominance
Answer: (c) Polygenic inheritance
Explanation: Polygenic inheritance refers to the inheritance of a trait that is controlled by multiple genes, each contributing to the final phenotype. An example of polygenic inheritance is human skin color, which is influenced by several genes working together.
- Which of the following disorders is caused by a mutation in a single gene but exhibits a late-onset phenotype?
a) Cystic fibrosis
b) Huntington’s disease
c) Hemophilia
d) Turner syndrome
Answer: (b) Huntington’s disease
Explanation: Huntington’s disease is caused by a mutation in a single gene, specifically a trinucleotide repeat expansion in the HTT gene. Symptoms typically do not appear until middle age, making it a late-onset genetic disorder. Cystic fibrosis and hemophilia also result from single-gene mutations, but they exhibit symptoms early in life, while Turner syndrome is a chromosomal disorder.
- What is the chromosomal composition of a female with Turner syndrome?
a) 46, XX
b) 45, X
c) 47, XXY
d) 46, XY
Answer: (b) 45, X
Explanation: Turner syndrome is caused by the complete or partial absence of one of the X chromosomes, leading to a 45, X genotype in affected females. This results in various developmental abnormalities, including short stature and infertility.
- Which of the following is an example of codominance?
a) Red and white flowers producing pink flowers in the F1 generation
b) A person with AB blood type
c) A cross between tall and short plants producing medium-height plants
d) A gene affecting multiple traits
Answer: (b) A person with AB blood type
Explanation: Codominance occurs when both alleles are fully expressed in a heterozygote. In individuals with blood type AB, both the A allele (IA) and B allele (IB) are expressed, resulting in a phenotype where both types of antigens are present on red blood cells. This is different from incomplete dominance, where the phenotype is a blend of the two alleles.
- Which of the following statements best describes pleiotropy?
a) A single gene affects multiple phenotypic traits
b) Multiple genes control a single trait
c) The effect of one gene masks the effect of another
d) Two genes are located on the same chromosome
Answer: (a) A single gene affects multiple phenotypic traits
Explanation: Pleiotropy occurs when one gene influences multiple, seemingly unrelated phenotypic traits. An example is Marfan syndrome, where a mutation in a single gene (FBN1) affects the connective tissues, leading to symptoms in different parts of the body such as the heart, eyes, and skeleton.
- In a cross between two pea plants (AaBb x AaBb), where A = yellow seeds, a = green seeds, B = round seeds, and b = wrinkled seeds, what fraction of the offspring will have green, wrinkled seeds?
a) 1/16
b) 3/16
c) 9/16
d) 12/16
Answer: (a) 1/16
Explanation: This is a dihybrid cross. The chance of inheriting the aa genotype (green seeds) is 1/4, and the chance of inheriting the bb genotype (wrinkled seeds) is also 1/4. The probability of both occurring together is 1/4 × 1/4 = 1/16. Thus, 1/16 of the offspring will have green, wrinkled seeds.
- A male with an extra Y chromosome (XYY) is expected to show which of the following characteristics?
a) Normal male phenotype with no significant symptoms
b) Female-like characteristics due to extra X chromosome
c) Increased incidence of Down syndrome
d) Severe mental retardation and developmental delays
Answer: (a) Normal male phenotype with no significant symptoms
Explanation: XYY syndrome, also known as 47, XYY, results in a male with an extra Y chromosome. Most males with this condition have normal physical development and fertility, and many do not display significant symptoms. Some may be taller than average, and a small percentage may have learning difficulties or behavioral issues.
- Which of the following best describes the law of segregation?
a) Each individual has two alleles for each gene, and these alleles separate during gamete formation
b) Genes located close together on the same chromosome are inherited together
c) The inheritance of one trait does not affect the inheritance of another
d) Alleles are exchanged between homologous chromosomes during crossing over
Answer: (a) Each individual has two alleles for each gene, and these alleles separate during gamete formation
Explanation: Mendel’s law of segregation states that each organism possesses two alleles for each gene, and during the formation of gametes, these alleles separate, so that each gamete contains only one allele for each gene. This is one of the key principles of Mendelian inheritance.
- Which of the following conditions is caused by a mutation in mitochondrial DNA?
a) Cystic fibrosis
b) Leber’s hereditary optic neuropathy
c) Huntington’s disease
d) Turner syndrome
Answer: (b) Leber’s hereditary optic neuropathy
Explanation: Leber’s hereditary optic neuropathy (LHON) is a mitochondrial genetic disorder that causes loss of vision. Mitochondrial DNA is inherited maternally, so disorders associated with mitochondrial mutations are passed from mothers to all of their offspring. Cystic fibrosis and Huntington’s disease are caused by nuclear gene mutations, while Turner syndrome is a chromosomal disorder.
- Which of the following terms describes genes that are located on the same chromosome and tend to be inherited together?
a) Alleles
b) Linkage
c) Epistasis
d) Codominance
Answer: (b) Linkage
Explanation: Linkage refers to the phenomenon where genes located close together on the same chromosome tend to be inherited together because they are less likely to be separated by crossing over during meiosis. This violates Mendel’s law of independent assortment, which applies only to genes located on different chromosomes.
- Which of the following is a characteristic feature of a recessive genetic disorder?
a) Only one copy of the mutated gene is necessary to cause the disorder
b) The disorder appears in every generation
c) Two copies of the mutated gene are required to express the disorder
d) The disorder is equally common in males and females when X-linked
Answer: (c) Two copies of the mutated gene are required to express the disorder
Explanation: A recessive genetic disorder requires two copies of the mutated allele for the disorder to be expressed. Individuals with one copy of the mutated allele and one normal allele are carriers but do not exhibit symptoms. These disorders often skip generations in pedigrees.
- Which of the following is an example of a sex-influenced trait?
a) Color blindness
b) Male-pattern baldness
c) Hemophilia
d) Sickle cell anemia
Answer: (b) Male-pattern baldness
Explanation: A sex-influenced trait is a trait that is expressed differently in males and females due to hormonal differences, even though the gene is not located on a sex chromosome. Male-pattern baldness is more common in males due to the influence of male hormones, but females can also express the trait if they have the necessary genetic combination.
- In the case of X-linked recessive inheritance, which of the following is true?
a) Affected males can pass the trait to their sons
b) Females are always carriers
c) Males are more likely to be affected than females
d) The trait is equally likely to affect males and females
Answer: (c) Males are more likely to be affected than females
Explanation: In X-linked recessive inheritance, males are more likely to be affected because they have only one X chromosome. If a male inherits the mutated allele on the X chromosome, he will express the trait since there is no second X chromosome to mask the effect. Females, who have two X chromosomes, are less likely to be affected because they need two copies of the mutated allele to express the trait.
- Which of the following terms refers to the failure of homologous chromosomes or sister chromatids to separate properly during meiosis?
a) Crossing over
b) Independent assortment
c) Non-disjunction
d) Linkage
Answer: (c) Non-disjunction
Explanation: Non-disjunction occurs when chromosomes fail to separate properly during meiosis I (homologous chromosomes) or meiosis II (sister chromatids). This results in gametes with an abnormal number of chromosomes, which can lead to conditions such as Down syndrome (trisomy 21) or Turner syndrome (45, X).
- What is the phenotypic ratio in the F2 generation of a dihybrid cross (AaBb x AaBb)?
a) 1:2:1
b) 3:1
c) 9:3:3:1
d) 1:1:1:1
Answer: (c) 9:3:3:1
Explanation: In a dihybrid cross, where two heterozygous individuals are crossed for two traits, the phenotypic ratio in the F2 generation is 9:3:3:1. This means that 9 offspring show both dominant traits, 3 show the dominant form of one trait and the recessive form of the other, another 3 show the opposite pattern, and 1 shows both recessive traits.
- Which of the following terms refers to the exchange of genetic material between homologous chromosomes during meiosis?
a) Independent assortment
b) Segregation
c) Crossing over
d) Non-disjunction
Answer: (c) Crossing over
Explanation: Crossing over is the process where homologous chromosomes exchange genetic material during prophase I of meiosis. This increases genetic diversity by creating new combinations of alleles in the resulting gametes.
- Which of the following best describes the law of independent assortment?
a) Each allele segregates independently of the others during gamete formation
b) The two alleles for a single trait separate during gamete formation
c) Genes located on the same chromosome are inherited together
d) Chromosomes fail to separate properly during meiosis
Answer: (a) Each allele segregates independently of the others during gamete formation
Explanation: Mendel’s law of independent assortment states that alleles for different genes are distributed independently of one another during the formation of gametes. This is true only if the genes are located on different chromosomes or far apart on the same chromosome.
- Which of the following traits is an example of polygenic inheritance?
a) Blood type
b) Height
c) Hemophilia
d) Color blindness
Answer: (b) Height
Explanation: Polygenic inheritance occurs when a trait is controlled by multiple genes. Height is an example of this, as it is determined by the interaction of several genes, each contributing to the overall phenotype. Blood type is controlled by a single gene with multiple alleles, and hemophilia and color blindness are examples of single-gene disorders.
- A cross between a red-flowered plant (RR) and a white-flowered plant (rr) produces all pink offspring. This is an example of:
a) Codominance
b) Incomplete dominance
c) Epistasis
d) Pleiotropy
Answer: (b) Incomplete dominance
Explanation: In incomplete dominance, the heterozygous offspring have a phenotype that is intermediate between the two parental phenotypes. In this case, crossing a red-flowered plant (RR) with a white-flowered plant (rr) results in pink flowers, as neither allele is completely dominant.
- Which of the following genetic disorders is inherited in an autosomal dominant manner?
a) Sickle cell anemia
b) Cystic fibrosis
c) Huntington’s disease
d) Hemophilia
Answer: (c) Huntington’s disease
Explanation: Huntington’s disease is caused by a dominant allele, meaning that only one copy of the mutated gene is required for the disorder to be expressed. Autosomal dominant disorders typically appear in every generation, and affected individuals have a 50% chance of passing the disorder to their offspring.
- Which of the following conditions is characterized by trisomy 13?
a) Down syndrome
b) Turner syndrome
c) Patau syndrome
d) Klinefelter syndrome
Answer: (c) Patau syndrome
Explanation: Patau syndrome is caused by trisomy 13, where individuals have three copies of chromosome 13. This leads to severe developmental issues and a low survival rate. Down syndrome is caused by trisomy 21, Turner syndrome by a missing X chromosome, and Klinefelter syndrome by an extra X chromosome in males (XXY).
- In a population that is in Hardy-Weinberg equilibrium, the frequency of the recessive allele is 0.4. What is the frequency of heterozygous individuals?
a) 0.16
b) 0.24
c) 0.48
d) 0.36
Answer: (c) 0.48
Explanation: The Hardy-Weinberg equation is p² + 2pq + q² = 1, where p is the frequency of the dominant allele and q is the frequency of the recessive allele. Given that q = 0.4, p = 1 – 0.4 = 0.6. The frequency of heterozygous individuals is given by 2pq = 2 × 0.6 × 0.4 = 0.48.
- Which of the following is true for a genetic disorder inherited in an autosomal recessive manner?
a) The disorder skips generations
b) Both males and females are equally affected
c) Individuals with one copy of the mutated allele are carriers
d) All of the above
Answer: (d) All of the above
Explanation: Autosomal recessive disorders require two copies of the mutated allele for the disorder to be expressed. These disorders often skip generations because carriers (heterozygous individuals) do not show symptoms. Both males and females are equally affected because the disorder is not sex-linked.
- Which of the following best describes a genetic mutation that causes a premature stop codon?
a) Missense mutation
b) Silent mutation
c) Frameshift mutation
d) Nonsense mutation
Answer: (d) Nonsense mutation
Explanation: A nonsense mutation occurs when a base substitution in the DNA sequence creates a stop codon (UAA, UAG, UGA) prematurely, leading to the early termination of protein synthesis. This usually results in a truncated, nonfunctional protein. In contrast, a missense mutation changes one amino acid, and a silent mutation has no effect on the protein sequence.
- The ABO blood group system in humans is an example of:
a) Polygenic inheritance
b) Codominance
c) Incomplete dominance
d) Epistasis
Answer: (b) Codominance
Explanation: The ABO blood group system exhibits codominance because both the A (IA) and B (IB) alleles are equally expressed in individuals with the AB blood type. Each allele codes for a different antigen on the surface of red blood cells, and both are expressed without blending, making it a clear example of codominance.
- Which of the following is NOT a feature of the genetic code?
a) Degeneracy
b) Universality
c) Non-overlapping
d) Overlapping
Answer: (d) Overlapping
Explanation: The genetic code is non-overlapping, meaning that each set of three nucleotides (codon) is read sequentially during translation without sharing nucleotides between adjacent codons. The code is also degenerate, meaning some amino acids are encoded by more than one codon, and it is nearly universal across organisms.
- In a pedigree chart, a shaded square represents:
a) An affected male
b) An affected female
c) A carrier male
d) A carrier female
Answer: (a) An affected male
Explanation: In a pedigree chart, squares represent males, and circles represent females. Shading indicates that the individual is affected by the trait being studied, while an unshaded symbol represents an unaffected individual. Carriers are sometimes indicated by a half-shaded symbol.
- Which of the following is an example of a disorder caused by a single-gene mutation?
a) Diabetes mellitus
b) Alzheimer’s disease
c) Cystic fibrosis
d) Schizophrenia
Answer: (c) Cystic fibrosis
Explanation: Cystic fibrosis is caused by a mutation in a single gene, the CFTR gene, which affects the function of chloride channels in cells. Other conditions like diabetes and Alzheimer’s are multifactorial, involving both genetic and environmental factors, while schizophrenia has a complex genetic basis involving many genes.
- What is the name of the enzyme responsible for unzipping the DNA double helix during replication?
a) DNA polymerase
b) Helicase
c) Ligase
d) Topoisomerase
Answer: (b) Helicase
Explanation: Helicase is the enzyme responsible for unwinding and separating the two strands of the DNA double helix during DNA replication. It breaks the hydrogen bonds between the complementary base pairs, allowing each strand to serve as a template for new DNA synthesis.
- If a woman with type O blood marries a man with type AB blood, what are the possible blood types of their offspring?
a) A and B
b) O and AB
c) A, B, and AB
d) O, A, B, and AB
Answer: (a) A and B
Explanation: The woman with type O blood has the genotype ii, and the man with type AB blood has the genotype IAIB. Their offspring can inherit either the IA or IB allele from the father and the i allele from the mother. Therefore, the possible blood types of the children are either A (IAi) or B (IBi).
- A condition where the same gene influences multiple, seemingly unrelated phenotypic traits is known as:
a) Polygenic inheritance
b) Codominance
c) Pleiotropy
d) Epistasis
Answer: (c) Pleiotropy
Explanation: Pleiotropy occurs when a single gene influences multiple, seemingly unrelated phenotypic traits. For example, a mutation in the gene responsible for producing the connective tissue protein fibrillin-1 can lead to Marfan syndrome, affecting the heart, skeleton, and eyes.
- Which of the following genetic disorders is caused by a deletion of a segment of chromosome 5?
a) Turner syndrome
b) Cri-du-chat syndrome
c) Down syndrome
d) Klinefelter syndrome
Answer: (b) Cri-du-chat syndrome
Explanation: Cri-du-chat syndrome is caused by a deletion of a portion of the short arm of chromosome 5. The condition is named for the characteristic cat-like cry of affected infants. Turner syndrome results from the absence of an X chromosome, Down syndrome from trisomy 21, and Klinefelter syndrome from an extra X chromosome in males (XXY).
- Which of the following processes occurs during prophase I of meiosis and contributes to genetic variation?
a) Segregation
b) Independent assortment
c) Crossing over
d) DNA replication
Answer: (c) Crossing over
Explanation: Crossing over occurs during prophase I of meiosis, where homologous chromosomes exchange segments of DNA. This process creates new combinations of alleles, contributing to genetic variation in the resulting gametes. Independent assortment also contributes to variation but occurs during metaphase I.
- Which of the following is a characteristic feature of Turner syndrome?
a) Extra X chromosome in males
b) Trisomy 21
c) Missing X chromosome in females
d) Trisomy 13
Answer: (c) Missing X chromosome in females
Explanation: Turner syndrome occurs when a female is missing one of her X chromosomes (45, X instead of 46, XX). Individuals with this condition often have short stature, delayed puberty, and infertility. Other choices represent different chromosomal disorders: Klinefelter syndrome (extra X chromosome in males), Down syndrome (trisomy 21), and Patau syndrome (trisomy 13).
- Which of the following is the expected phenotypic ratio for a monohybrid cross involving incomplete dominance?
a) 3:1
b) 9:3:3:1
c) 1:2:1
d) 1:1:1:1
Answer: (c) 1:2:1
Explanation: In incomplete dominance, the heterozygous phenotype is a blend of the two homozygous phenotypes. A cross between two heterozygous individuals (e.g., Rr) results in a 1:2:1 ratio: 1 showing the dominant phenotype, 2 showing the intermediate (heterozygous) phenotype, and 1 showing the recessive phenotype.
- The process of RNA synthesis from a DNA template is called:
a) Translation
b) Transcription
c) Replication
d) Reverse transcription
Answer: (b) Transcription
Explanation: Transcription is the process by which RNA is synthesized from a DNA template. During this process, RNA polymerase reads the DNA sequence and synthesizes a complementary strand of messenger RNA (mRNA). Translation is the process where mRNA is used to synthesize proteins.
- In the lac operon of E. coli, what is the role of the lac repressor protein?
a) It promotes the transcription of the lac operon genes
b) It inhibits the transcription of the lac operon genes
c) It binds to lactose to initiate transcription
d) It degrades lactose
Answer: (b) It inhibits the transcription of the lac operon genes
Explanation: The lac repressor protein binds to the operator region of the lac operon, preventing RNA polymerase from transcribing the genes necessary for lactose metabolism. When lactose is present, it binds to the repressor, causing it to release from the operator, allowing transcription to occur.
- A gene located on the X chromosome is referred to as:
a) Autosomal
b) X-linked
c) Y-linked
d) Homologous
Answer: (b) X-linked
Explanation: Genes located on the X chromosome are called X-linked genes. Males have only one X chromosome, so a single copy of a recessive allele on the X chromosome can cause an X-linked disorder, such as color blindness or hemophilia. Females have two X chromosomes, so they can be carriers if only one X chromosome has the mutation.
- Which of the following genetic disorders is caused by a frameshift mutation?
a) Sickle cell anemia
b) Huntington’s disease
c) Cystic fibrosis
d) Tay-Sachs disease
Answer: (d) Tay-Sachs disease
Explanation: Tay-Sachs disease is caused by a frameshift mutation in the HEXA gene, leading to a defective enzyme (hexosaminidase A) that results in the accumulation of harmful substances in the nervous system. Frameshift mutations involve insertions or deletions of nucleotides that alter the reading frame of the genetic code, severely affecting protein function.
- If two carriers for an autosomal recessive genetic disorder (Aa x Aa) have children, what is the probability that their child will be affected?
a) 100%
b) 50%
c) 25%
d) 75%
Answer: (c) 25%
Explanation: In an autosomal recessive inheritance pattern, both parents must carry one copy of the mutated gene (Aa). When two heterozygotes mate, there is a 25% chance (aa) that their offspring will inherit two copies of the recessive allele and express the disorder, a 50% chance (Aa) that they will be carriers, and a 25% chance (AA) of being unaffected.
- Which process explains why children inherit half of their genetic information from each parent?
a) Mitosis
b) Fertilization
c) Meiosis
d) Crossing over
Answer: (c) Meiosis
Explanation: Meiosis is the process that reduces the chromosome number by half, producing gametes (sperm and eggs) with 23 chromosomes each in humans. During fertilization, the gametes from both parents combine to form a zygote with 46 chromosomes (half from each parent). This ensures that offspring inherit genetic information from both parents.
- Which of the following is an example of codominance in humans?
a) ABO blood groups
b) Skin color
c) Eye color
d) Height
Answer: (a) ABO blood groups
Explanation: In codominance, both alleles are expressed equally in the phenotype. The ABO blood group system is a classic example where both IA and IB alleles are expressed equally in individuals with the AB blood type. Skin color and height are examples of polygenic traits, and eye color involves simple dominance.
- In Hardy-Weinberg equilibrium, if the frequency of the recessive allele (q) is 0.3, what is the frequency of homozygous dominant individuals?
a) 0.09
b) 0.49
c) 0.42
d) 0.21
Answer: (b) 0.49
Explanation: The Hardy-Weinberg equation is p² + 2pq + q² = 1, where p is the frequency of the dominant allele and q is the frequency of the recessive allele. If q = 0.3, then p = 1 – 0.3 = 0.7. The frequency of homozygous dominant individuals is p² = 0.7² = 0.49.
- Which genetic principle explains why siblings differ genetically from each other even though they have the same parents?
a) Segregation
b) Independent assortment
c) Crossing over
d) All of the above
Answer: (d) All of the above
Explanation: All of these processes contribute to genetic variation among siblings. During meiosis, segregation ensures that alleles are distributed randomly to gametes, independent assortment ensures that different genes are inherited independently, and crossing over creates new combinations of alleles by exchanging genetic material between homologous chromosomes.
- The condition where an individual has an extra chromosome (e.g., 47 chromosomes instead of the normal 46) is called:
a) Monosomy
b) Trisomy
c) Nullisomy
d) Tetrasomy
Answer: (b) Trisomy
Explanation: Trisomy refers to the presence of an extra chromosome, resulting in three copies of a particular chromosome instead of the normal two. Down syndrome (trisomy 21) is a well-known example. Monosomy refers to the absence of one chromosome, while tetrasomy refers to the presence of an extra pair of chromosomes.
- Which of the following genetic disorders is caused by a frameshift mutation?
a) Cystic fibrosis
b) Duchenne muscular dystrophy
c) Sickle cell anemia
d) Huntington’s disease
Answer: (b) Duchenne muscular dystrophy
Explanation: Duchenne muscular dystrophy is caused by a frameshift mutation in the dystrophin gene, leading to the production of a nonfunctional dystrophin protein. Frameshift mutations occur when nucleotides are inserted or deleted from the DNA sequence, altering the reading frame of the gene. Cystic fibrosis and sickle cell anemia are caused by point mutations, while Huntington’s disease is caused by a repeat expansion.
- Which of the following is true regarding linkage?
a) Linked genes do not follow Mendel’s law of independent assortment
b) Linked genes are located on the same chromosome
c) Linked genes tend to be inherited together
d) All of the above
Answer: (d) All of the above
Explanation: Linked genes are located on the same chromosome and tend to be inherited together because they are close to each other and do not segregate independently during meiosis. This violates Mendel’s law of independent assortment, which states that genes located on different chromosomes assort independently.
- A person with Klinefelter syndrome has which of the following karyotypes?
a) 45, X
b) 47, XXY
c) 47, XXX
d) 45, Y
Answer: (b) 47, XXY
Explanation: Klinefelter syndrome is characterized by the presence of an extra X chromosome in males (47, XXY). Individuals with this condition typically have male physical characteristics but may experience infertility and other symptoms. 45, X is the karyotype for Turner syndrome, while 47, XXX is for triple X syndrome.
- Which of the following processes results in the exchange of genetic material between non-sister chromatids during meiosis?
a) Independent assortment
b) Segregation
c) Crossing over
d) Nondisjunction
Answer: (c) Crossing over
Explanation: Crossing over occurs during prophase I of meiosis when non-sister chromatids of homologous chromosomes exchange segments of genetic material. This process increases genetic variation by producing new combinations of alleles. Independent assortment and segregation also contribute to genetic variation, but nondisjunction refers to the failure of chromosomes to separate properly during meiosis.
- In a dihybrid cross, which of the following Mendelian principles is demonstrated by the 9:3:3:1 phenotypic ratio?
a) Law of segregation
b) Law of dominance
c) Law of independent assortment
d) Law of codominance
Answer: (c) Law of independent assortment
Explanation: The 9:3:3:1 ratio in a dihybrid cross demonstrates Mendel’s law of independent assortment, which states that alleles for different genes assort independently of each other during gamete formation. This leads to the different combinations of traits observed in the offspring. The law of segregation applies to a monohybrid cross.
- Which chromosomal condition is associated with Down syndrome?
a) Trisomy 21
b) Monosomy X
c) Trisomy 18
d) Trisomy 13
Answer: (a) Trisomy 21
Explanation: Down syndrome is caused by an extra copy of chromosome 21, also known as trisomy 21. Individuals with this condition have 47 chromosomes instead of the usual 46. Trisomy 18 causes Edwards syndrome, and trisomy 13 causes Patau syndrome. Monosomy X results in Turner syndrome.
- What is the probability that a son will inherit a Y-linked trait from his father?
a) 0%
b) 25%
c) 50%
d) 100%
Answer: (d) 100%
Explanation: Y-linked traits are carried on the Y chromosome, which is passed directly from father to son. Since males inherit their Y chromosome exclusively from their fathers, a son will always inherit any Y-linked traits his father carries, resulting in a 100% chance of inheritance.
- If a man with blood type A (genotype IAi) marries a woman with blood type B (genotype IBi), what is the probability that their child will have blood type AB?
a) 0%
b) 25%
c) 50%
d) 75%
Answer: (b) 25%
Explanation: The possible genotypes of the child from a cross between IAi (blood type A) and IBi (blood type B) are IAIB (AB), IAi (A), IBi (B), and ii (O). Therefore, the probability of the child having blood type AB (IAIB) is 25%.
- Which of the following techniques is used to separate DNA fragments based on size?
a) PCR (Polymerase Chain Reaction)
b) Gel electrophoresis
c) DNA sequencing
d) Cloning
Answer: (b) Gel electrophoresis
Explanation: Gel electrophoresis is a technique used to separate DNA fragments based on size. DNA fragments are placed in a gel and subjected to an electric field, which causes them to move. Smaller fragments move faster through the gel, allowing separation by size. PCR amplifies DNA, DNA sequencing determines the nucleotide order, and cloning produces copies of DNA.
- Which enzyme is responsible for sealing the gaps between Okazaki fragments during DNA replication?
a) Helicase
b) DNA polymerase
c) Primase
d) DNA ligase
Answer: (d) DNA ligase
Explanation: DNA ligase is the enzyme responsible for sealing the gaps between Okazaki fragments on the lagging strand during DNA replication. It forms covalent bonds between adjacent nucleotides to create a continuous strand of DNA. Helicase unwinds the DNA, primase synthesizes RNA primers, and DNA polymerase adds nucleotides to the growing DNA chain.
- Which of the following statements about genetic drift is true?
a) It results from natural selection
b) It has a larger effect in small populations
c) It increases genetic variation within populations
d) It only occurs in large populations
Answer: (b) It has a larger effect in small populations
Explanation: Genetic drift is a random change in allele frequencies in a population, and it has a greater effect in small populations because chance events can significantly alter the gene pool. Unlike natural selection, genetic drift does not necessarily lead to adaptation and can reduce genetic variation within populations over time.
- Which of the following phenomena results in the movement of alleles between populations?
a) Genetic drift
b) Gene flow
c) Natural selection
d) Mutation
Answer: (b) Gene flow
Explanation: Gene flow is the movement of alleles between populations, often due to migration. It can introduce new alleles into a population, increasing genetic diversity. Genetic drift is a random change in allele frequencies, natural selection favors beneficial traits, and mutation introduces new genetic variations.
- Which of the following disorders is caused by nondisjunction during meiosis?
a) Sickle cell anemia
b) Hemophilia
c) Down syndrome
d) Cystic fibrosis
Answer: (c) Down syndrome
Explanation: Down syndrome is caused by nondisjunction during meiosis, which results in an extra copy of chromosome 21 (trisomy 21). Nondisjunction occurs when chromosomes fail to separate properly during meiosis, leading to gametes with abnormal numbers of chromosomes. Sickle cell anemia, hemophilia, and cystic fibrosis are caused by specific gene mutations.
- Which of the following statements about the human genome is correct?
a) Humans have about 10,000 genes
b) The majority of the genome consists of protein-coding genes
c) Humans have 23 pairs of chromosomes
d) The Y chromosome is larger than the X chromosome
Answer: (c) Humans have 23 pairs of chromosomes
Explanation: Humans have 23 pairs of chromosomes, for a total of 46. The human genome contains about 20,000 to 25,000 genes, and the majority of the genome consists of non-coding DNA rather than protein-coding genes. The Y chromosome is smaller than the X chromosome.
- Which of the following describes the inheritance pattern of mitochondrial DNA?
a) Paternal inheritance
b) Maternal inheritance
c) Autosomal inheritance
d) X-linked inheritance
Answer: (b) Maternal inheritance
Explanation: Mitochondrial DNA is inherited exclusively from the mother because mitochondria are passed down through the egg cell. This type of inheritance is known as maternal inheritance. Paternal inheritance refers to traits passed down through the father, and autosomal and X-linked inheritance refer to nuclear genes.
- What is the main function of tRNA during translation?
a) Carries amino acids to the ribosome
b) Catalyzes the formation of peptide bonds
c) Synthesizes mRNA from a DNA template
d) Protects mRNA from degradation
Answer: (a) Carries amino acids to the ribosome
Explanation: Transfer RNA (tRNA) is responsible for carrying amino acids to the ribosome during translation. Each tRNA molecule has an anticodon that pairs with a specific codon on the mRNA, ensuring that the correct amino acid is added to the growing polypeptide chain. Ribosomes catalyze the formation of peptide bonds.
- Which of the following types of RNA is involved in splicing introns from pre-mRNA?
a) tRNA
b) mRNA
c) rRNA
d) snRNA
Answer: (d) snRNA
Explanation: Small nuclear RNA (snRNA) is involved in splicing introns from pre-mRNA during the process of RNA processing. This occurs in the spliceosome, where snRNA helps recognize the splice sites and remove introns. tRNA is involved in translation, mRNA carries genetic information, and rRNA forms part of the ribosome.
- Which of the following techniques is used to amplify a specific segment of DNA?
a) Gel electrophoresis
b) PCR (Polymerase Chain Reaction)
c) DNA sequencing
d) Restriction enzyme digestion
Answer: (b) PCR (Polymerase Chain Reaction)
Explanation: PCR is a technique used to amplify a specific segment of DNA, producing millions of copies of the target sequence. It involves repeated cycles of heating and cooling to denature the DNA, anneal primers, and extend the DNA with the help of DNA polymerase. Gel electrophoresis separates DNA fragments, DNA sequencing determines the sequence, and restriction enzymes cut DNA
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