Question 1

Why was Drosophila melanogaster (the fruit fly) such a valuable model organism for Thomas Hunt Morgan's genetic studies?

Accepted Answer

It has a short generation time, easily observable traits, and produces many offspring.

Question 2

Which of the following discoveries was confirmed by Morgan's fruit fly experiments?

Accepted Answer

Genes are located on chromosomes.

Question 3

What is genetic linkage?

Accepted Answer

The phenomenon where genes located close together on the same chromosome tend to be inherited together.

Question 4

How is the map distance between two linked genes calculated?

Accepted Answer

By counting the number of recombinant offspring and using the formula $$	ext{Map distance (cM)} = \frac{	ext{Number of recombinants}}{	ext{Total offspring}} 	imes 100$$

Question 5

A female who is heterozygous for the X-linked color blindness gene (X	extsuperscript{N}X	extsuperscript{n}) and a normal male (X	extsuperscript{N}Y) have children. What is the probability that a son will be color blind?

Accepted Answer

$$0.25$$

Question 6

Which of the following is an example of a chromosomal structural abnormality?

Accepted Answer

Inversion

Question 7

What is the Philadelphia chromosome?

Accepted Answer

A specific translocation between chromosomes 9 and 22 associated with chronic myelogenous leukemia.

Question 8

Which of the following best describes aneuploidy?

Accepted Answer

A condition in which an organism has one or more extra or missing chromosomes.

Question 9

A plant species normally has 2n = 14 chromosomes. A mutant is found with 2n = 21 chromosomes. What is this an example of?

Accepted Answer

Polyploidy

Question 10

Which of the following is an example of epigenetic inheritance?

Accepted Answer

Methylation of DNA that silences gene expression and is passed to offspring.

Question 11

What is X-inactivation and why is it important in mammals?

Accepted Answer

It is the random inactivation of one X chromosome in females, ensuring dosage compensation between males and females.

Question 12

A calico cat has patches of orange and black fur due to X-inactivation. Which genetic principle does this illustrate?

Accepted Answer

Mosaicism resulting from random X-inactivation in heterozygous females.

Question 13

Which of the following is true about mitochondrial (cytoplasmic) inheritance?

Accepted Answer

It is inherited exclusively from the mother.

Question 14

A woman with a mitochondrial disorder has children with a healthy man. What is the probability that her children will inherit the disorder?

Accepted Answer

All of her children will inherit the disorder.

Question 15

If a gene is imprinted, what does this mean?

Accepted Answer

It is expressed in a parent-of-origin-specific manner due to epigenetic modifications.

Question 16

A male with Klinefelter syndrome has the karyotype 47,XXY. Which chromosomal abnormality does this represent?

Accepted Answer

Aneuploidy

Question 17

Which of the following scenarios best illustrates the concept of linkage?

Accepted Answer

Two genes located close together on the same chromosome are often inherited together in offspring.

Question 18

A geneticist observes that two genes are 10 centimorgans (cM) apart. What percentage of offspring would you expect to be recombinant for these genes?

Accepted Answer

$$10\%$$

Question 19

Which of the following is NOT a possible consequence of chromosomal inversion?

Accepted Answer

Increased recombination between inverted segments.

Question 20

A woman who is a carrier for hemophilia (an X-linked recessive disorder) marries a normal man. What is the probability that their daughter will have hemophilia?

Accepted Answer

$$0$$

Chapter 12: The Chromosomal Basis of Inheritance – Study Guide

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