Q: A testcross between a dihybrid Drosophila (b extsuperscript{+}b vg extsuperscript{+}vg) and a double mutant (bb vgvg) produces 965 gray-normal, 944 black-vestigial, 206 gray-vestigial, and 185 black-normal offspring. What is the recombination frequency between the body color and wing shape genes?

$$\frac{206 + 185}{965 + 944 + 206 + 185} \times 100 = 17\%$$

Question 1

Which of the following best explains why Morgan chose Drosophila melanogaster (fruit flies) for his genetic experiments?

Accepted Answer

They have a short generation time and only four pairs of chromosomes, making them ideal for genetic studies.

Question 2

A woman who is heterozygous for the X-linked allele causing color blindness (X	extsuperscript{N}X	extsuperscript{n}) marries a man with normal vision (X	extsuperscript{N}Y). What is the probability that their son will be color blind?

Accepted Answer

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

Question 3

Which chromosomal abnormality is most commonly associated with Down syndrome?

Accepted Answer

Trisomy 21

Question 4

If a female cat is heterozygous for the X-linked gene controlling fur color, what is the most likely explanation for her patchy fur coloration?

Accepted Answer

Random inactivation of one X chromosome in each cell during embryonic development

Question 5

Which of the following best describes the law of independent assortment?

Accepted Answer

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

Question 6

A testcross between a dihybrid Drosophila (b	extsuperscript{+}b vg	extsuperscript{+}vg) and a double mutant (bb vgvg) produces 965 gray-normal, 944 black-vestigial, 206 gray-vestigial, and 185 black-normal offspring. What is the recombination frequency between the body color and wing shape genes?

Accepted Answer

$$\frac{206 + 185}{965 + 944 + 206 + 185} 	imes 100 = 17\%$$

Question 7

Which chromosomal event is responsible for producing recombinant offspring in a dihybrid testcross?

Accepted Answer

Crossing over between homologous chromosomes during meiosis I

Question 8

A male with Klinefelter syndrome has which of the following karyotypes?

Accepted Answer

XXY

Question 9

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

Accepted Answer

Half the gametes are normal, one is n+1, and one is n-1

Question 10

Which type of chromosomal alteration is illustrated by a segment of chromosome 5 being missing, as seen in cri du chat syndrome?

Accepted Answer

Deletion

Question 11

A reciprocal translocation between chromosomes 9 and 22 is associated with which human disorder?

Accepted Answer

Chronic myelogenous leukemia (CML)

Question 12

Which of the following statements about polyploidy is correct?

Accepted Answer

Polyploidy is more common in plants than in animals.

Question 13

Which gene on the Y chromosome is responsible for the development of testes in human embryos?

Accepted Answer

SRY gene

Question 14

A woman with Turner syndrome has which of the following chromosomal constitutions?

Accepted Answer

XO

Question 15

Which of the following best describes a Barr body?

Accepted Answer

An inactivated X chromosome in a female cell

Question 16

If a gene is located on the X chromosome and is recessive, which of the following is true about its expression in males?

Accepted Answer

It will always be expressed if present, since males have only one X chromosome.

Question 17

Which of the following is an example of aneuploidy?

Accepted Answer

A human cell with 47 chromosomes due to an extra chromosome 21

Question 18

Which of the following best explains why some types of aneuploidy are more survivable than others in humans?

Accepted Answer

Some chromosomes carry fewer essential genes, so their imbalance is less detrimental.

Question 19

Which of the following is true about linked genes?

Accepted Answer

They are located close together on the same chromosome and tend to be inherited together.

The Chromosomal Basis of Inheritance

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