Question 1

Which experimental organism did Thomas Hunt Morgan use to provide the first solid evidence associating a specific gene with a specific chromosome, and what was the first mutant phenotype he discovered?

Accepted Answer

Fruit fly (Drosophila melanogaster); white eyes

Question 2

Which of the following best explains why fruit flies (Drosophila melanogaster) are a convenient organism for genetic studies?

Accepted Answer

They have only four pairs of chromosomes, short lifecycles, and produce many offspring.

Question 3

Morgan’s experiment with white-eyed male flies and red-eyed female flies resulted in F$$_2$$ generation where only males had white eyes. What genetic principle does this illustrate?

Accepted Answer

Sex-linked inheritance with the gene located on the X chromosome

Question 4

Which law of Mendel is explained by the separation of homologous chromosomes during meiosis?

Accepted Answer

Law of Segregation

Question 5

A woman who is heterozygous for the X-linked recessive allele for color blindness (X$$^NX$^c) $$marries a man with normal vision (X$$^NY). $$What is the probability that their son will be color blind?

Accepted Answer

$$\frac{1}{2}$$

Question 6

Which of the following statements about the SRY gene is correct?

Accepted Answer

It encodes a protein that initiates male development by switching on other genes for testes formation.

Question 7

In birds, which sex chromosome combination determines a female?

Accepted Answer

WZ

Question 8

Which of the following genetic disorders is caused by a recessive allele on the X chromosome and is characterized by the inability to clot blood properly?

Accepted Answer

Hemophilia A

Question 9

What is the biological significance of X inactivation in female mammals?

Accepted Answer

It equalizes the expression of X-linked genes between males and females by condensing one X chromosome into a Barr body.

Question 10

A calico cat has patches of black and orange fur due to X inactivation. Why are almost all calico cats female?

Accepted Answer

Because males have only one X chromosome and cannot be heterozygous for the fur color gene.

Question 11

Linked genes tend to be inherited together because:

Accepted Answer

They are located near each other on the same chromosome.

Question 12

If two genes are located far apart on the same chromosome, what is the expected effect on their recombination frequency?

Accepted Answer

It will be higher, approaching the frequency for genes on different chromosomes.

Question 13

Which chromosomal alteration is associated with chronic myelogenous leukemia (CML)?

Accepted Answer

Translocation between chromosomes 9 and 22 (Philadelphia chromosome)

Question 14

A child is born with only one copy of chromosome 7. What is this condition called?

Accepted Answer

Monosomy

Question 15

Which of the following is true about polyploidy?

Accepted Answer

It results in organisms with more than two complete sets of chromosomes.

Question 16

Which chromosomal alteration involves a fragment joining a non-homologous chromosome, potentially altering gene expression?

Accepted Answer

Translocation

Question 17

If a gene coded for alanine with the sequence C-G-G, and the cytosine nucleotide was deleted, what type of chromosomal alteration has occurred and what is the likely effect?

Accepted Answer

Deletion; alanine will not be produced

Question 18

Which of the following is a consequence of nondisjunction during meiosis?

Accepted Answer

Some gametes will have an abnormal number of chromosomes, leading to aneuploidy.

Question 19

Which of the following best describes the difference between germline and somatic mutations?

Accepted Answer

Germline mutations occur in cells that give rise to gametes and are heritable; somatic mutations occur in nonsex cells and are not passed to offspring.

Question 20

A geneticist observes that two traits in fruit flies, body color and wing size, are usually inherited together but sometimes appear in new combinations. What process explains the appearance of these nonparental phenotypes?

Accepted Answer

Genetic recombination due to crossing over

Chapter 15: Chromosomal Basis of Inheritance

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