Question 1

Which of the following best describes Mendel’s principle of independent assortment?

Accepted Answer

Alleles of genes on nonhomologous chromosomes assort independently during gamete formation.

Question 2

A heterozygous pea plant for seed color (Yy) and seed shape (Rr) is self-crossed. According to Mendel’s laws, what is the expected phenotypic ratio in the F2 generation?

Accepted Answer

$$9:3:3:1$$

Question 3

Which experimental observation provided the first evidence that genes are located on chromosomes?

Accepted Answer

Observation of sex-linked inheritance of eye color in Drosophila

Question 4

In Morgan’s Drosophila experiments, why were white-eyed females rare in the F2 generation?

Accepted Answer

The gene for eye color is located on the X chromosome and requires two copies of the mutant allele in females.

Question 5

Which of the following is a direct consequence of non-disjunction during meiosis?

Accepted Answer

Aneuploidy, such as trisomy or monosomy

Question 6

A human male with Klinefelter syndrome has the following karyotype:

Accepted Answer

$$47, XXY$$

Question 7

Which process ensures that males and females have the same effective dose of X-linked gene products?

Accepted Answer

X-inactivation (dosage compensation)

Question 8

A woman who is heterozygous for the X-linked gene for red-green color blindness has children with a man who has normal vision. What is the probability that their son will be colorblind?

Accepted Answer

$$0.25$$

Question 9

Which of the following best explains why X-linked recessive disorders are more common in males than females?

Accepted Answer

Males only need one copy of the mutant allele to express the disorder.

Question 10

If non-disjunction occurs during meiosis II in oogenesis, which of the following gametes could be produced?

Accepted Answer

Gametes with two copies of the same chromosome

Question 11

Which of the following terms describes an organism with one extra chromosome (e.g., 2n+1)?

Accepted Answer

Trisomy

Question 12

What is the function of the XIST gene in female mammals?

Accepted Answer

It produces RNA that coats and inactivates one X chromosome.

Question 13

Which of the following is true about pseudoautosomal regions?

Accepted Answer

They are regions of homology between the X and Y chromosomes.

Question 14

A female mammal heterozygous for an X-linked gene displays a mosaic phenotype. What is the underlying cause?

Accepted Answer

Random X-inactivation in each cell

Question 15

Which of the following best describes the chromosomal theory of inheritance?

Accepted Answer

Genes are located on chromosomes and their behavior during meiosis explains inheritance patterns.

Question 16

If a human oocyte completes meiosis I but fails to separate homologous chromosomes, what is the likely outcome for the resulting zygote if fertilized?

Accepted Answer

The zygote may be aneuploid, such as trisomic or monosomic.

Question 17

Which of the following is a reason why X-chromosome aneuploidies are less severe than autosomal aneuploidies?

Accepted Answer

X-inactivation can silence extra X chromosomes.

Question 18

Which of the following best explains why Down syndrome is more common in children born to older mothers?

Accepted Answer

The risk of chromosome non-disjunction increases with maternal age due to prolonged arrest in prophase I.

Question 19

Which of the following is NOT a feature of Klinefelter syndrome?

Accepted Answer

Short stature

Question 20

Which of the following best describes the outcome of crossing over during meiosis?

Accepted Answer

It increases genetic diversity by exchanging genetic material between homologous chromosomes.

Chromosomal Theory of Inheritance and Sex Determination

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