Q: A testcross between a dihybrid Drosophila (gray body, normal wings) and a double mutant (black body, vestigial wings) produces 965 gray-normal, 944 black-vestigial, 206 gray-vestigial, and 185 black-normal offspring. What is the recombination frequency between the two genes?

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

Question 1

Which of the following best explains why Drosophila melanogaster (fruit flies) were an ideal organism for Thomas Hunt Morgan's genetic experiments?

Accepted Answer

They have only four pairs of chromosomes, making genetic analysis simpler.

Question 2

A male with the genotype $$X^nY$$ for a gene causing color blindness (where $$X^N is $$normal vision and $$X^n is $$color blindness) marries a female with genotype $$X^N X^n. $$What is the probability that their son will be color blind?

Accepted Answer

$$0.25$$

Question 3

Which chromosomal event is responsible for the production of recombinant phenotypes in a dihybrid testcross, as observed by Morgan in Drosophila?

Accepted Answer

Crossing over between homologous chromosomes during prophase I

Question 4

A woman who is heterozygous for an X-linked recessive disorder (carrier) has children with a man who does not have the disorder. What is the expected proportion of affected sons?

Accepted Answer

$$0.25$$

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 (gray body, normal wings) and a double mutant (black body, vestigial wings) produces 965 gray-normal, 944 black-vestigial, 206 gray-vestigial, and 185 black-normal offspring. What is the recombination frequency between the two genes?

Accepted Answer

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

Question 7

Which chromosomal abnormality is associated with Down syndrome?

Accepted Answer

Trisomy 21

Question 8

A female calico cat is an example of which genetic phenomenon?

Accepted Answer

Random X chromosome inactivation

Question 9

Which of the following is true about the SRY gene?

Accepted Answer

It is located on the Y chromosome and triggers male development.

Question 10

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

Accepted Answer

Deletion

Question 11

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

Accepted Answer

XXY

Question 12

Which of the following best describes aneuploidy?

Accepted Answer

A condition in which an organism has an abnormal number of chromosomes.

Question 13

Which of the following is a likely result of nondisjunction during meiosis II?

Accepted Answer

Two normal gametes, one gamete with $$n+1$$ chromosomes, and one gamete with $$n-1$$ chromosomes.

Question 14

Which of the following statements about polyploidy is correct?

Accepted Answer

Polyploidy is more common in plants than in animals.

Question 15

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

Accepted Answer

Chronic myelogenous leukemia (CML)

Question 16

If a gene is located on the Y chromosome, which of the following statements is true?

Accepted Answer

It can only be inherited from father to son.

Question 17

Which of the following best explains why linked genes do not assort independently?

Accepted Answer

They are located close together on the same chromosome.

Question 18

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

Accepted Answer

45, X

Question 19

Which of the following is a possible outcome if a segment of a chromosome is duplicated?

Accepted Answer

The chromosome will have two copies of the same gene segment.

Question 20

Which of the following best describes the difference between parental types and recombinant types in a genetic cross?

Accepted Answer

Parental types have phenotypes matching the original parents, while recombinant types have new combinations of traits.

Chapter 15 Biology

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