- 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.
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