- 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%.
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