Question 1

Which of the following best explains why Klinefelter syndrome (47, XXY) individuals exhibit some female secondary sex characteristics despite having a Y chromosome?

Accepted Answer

The extra X chromosome is not completely inactivated, and some genes escape inactivation, leading to partial feminization.

Question 2

In Drosophila, what is the expected sexual phenotype of an individual with the chromosome composition $$3X:2A$$?

Accepted Answer

Metafemale

Question 3

Which of the following is a direct consequence of nondisjunction during meiosis I in humans?

Accepted Answer

All gametes will be aneuploid, with two gametes having an extra chromosome and two missing that chromosome.

Question 4

Which of the following statements about dosage compensation in mammals is correct?

Accepted Answer

Dosage compensation is achieved by inactivating one X chromosome in each somatic cell of females.

Question 5

A plant breeder crosses a diploid species (2n) with a related tetraploid species (4n) and obtains a sterile triploid hybrid. Which process could restore fertility to this hybrid?

Accepted Answer

Inducing chromosome doubling to produce a tetraploid (4n)

Question 6

Which of the following best describes the Lyon hypothesis?

Accepted Answer

X-inactivation occurs randomly in somatic cells early in embryonic development, and all descendant cells maintain the same inactive X.

Question 7

A child is born with the karyotype 47, XXY. Which of the following is the most likely explanation for this chromosomal abnormality?

Accepted Answer

Nondisjunction of the sex chromosomes during meiosis in either parent

Question 8

Which of the following is a characteristic of mitochondrial DNA (mtDNA) that makes it more susceptible to mutations compared to nuclear DNA?

Accepted Answer

mtDNA lacks histone protection and has limited DNA repair mechanisms.

Question 9

Which of the following best explains the inheritance pattern of the variegated leaf phenotype in Mirabilis jalapa (four o’clock plant)?

Accepted Answer

It is determined by mutations in chloroplast DNA inherited from the ovule (maternal parent).

Question 10

Which of the following is a likely outcome of a reciprocal translocation in a human carrier during meiosis?

Accepted Answer

Some gametes will have duplications and deficiencies, leading to semisterility.

Question 11

Which of the following is true regarding the maternal effect in Lymnaea peregra (snail) shell coiling?

Accepted Answer

The phenotype of the offspring is determined by the genotype of the mother, regardless of her phenotype.

Question 12

Which of the following best describes the effect of a paracentric inversion crossover during meiosis?

Accepted Answer

It produces one dicentric chromatid and one acentric chromatid among the recombinants.

Question 13

A human cell is observed to have two Barr bodies. What is the most likely karyotype of this cell?

Accepted Answer

47, XXX

Question 14

Which of the following is a key feature of the endosymbiotic theory regarding the origin of mitochondria and chloroplasts?

Accepted Answer

Mitochondria and chloroplasts arose from free-living bacteria engulfed by ancestral eukaryotic cells.

Question 15

Which of the following is a consequence of a deletion (deficiency) in a chromosome?

Accepted Answer

It can unmask recessive lethal alleles, leading to haploinsufficiency.

Question 16

Which of the following is a characteristic of copy number variants (CNVs) in the human genome?

Accepted Answer

They represent quantitative differences in the number of large DNA sequences and can affect both coding and noncoding regions.

Question 17

Which of the following is a requirement for a human disease to be classified as a mitochondrial DNA (mtDNA) disorder?

Accepted Answer

The disorder must reflect a deficiency in the bioenergetic function of the organelle.

Question 18

Which of the following best describes the inheritance pattern of Leber’s hereditary optic neuropathy (LHON)?

Accepted Answer

Mitochondrial (maternal) inheritance

Sex Determination, Chromosomal Variation, and Extranuclear Inheritance

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