Question 1

Which of the following best explains why Morgan chose Drosophila melanogaster for his genetic studies?

Accepted Answer

They have a short generation time and produce many offspring.

Question 2

A gene located on the X chromosome is called:

Accepted Answer

A sex-linked gene

Question 3

If a male fruit fly with a mutant allele on the X chromosome mates with a wild-type female, which of the following is true regarding the inheritance of the allele?

Accepted Answer

All female offspring will inherit the allele.

Question 4

In mammalian females, what is the fate of one of the two X chromosomes in each cell during embryonic development?

Accepted Answer

It condenses into a Barr body and becomes inactivated.

Question 5

A female who is heterozygous for a gene located on the X chromosome will be a mosaic for that character. This is due to:

Accepted Answer

Random inactivation of one X chromosome in each cell.

Question 6

Which of the following statements about linked genes is correct?

Accepted Answer

Linked genes are located on the same chromosome and tend to be inherited together.

Question 7

Morgan observed that some offspring had nonparental phenotypes in his testcrosses. What process explains this observation?

Accepted Answer

Crossing over between homologous chromosomes

Question 8

If two genes are 10 map units apart on a chromosome, what is the expected recombination frequency between them?

Accepted Answer

$$0.1 or$$ $$10\%$$

Question 9

Which of the following best describes a trisomic zygote?

Accepted Answer

It has three copies of a particular chromosome.

Question 10

A plant species is found to have four complete sets of chromosomes in each cell. This condition is known as:

Accepted Answer

Tetraploidy ($$4n)$$

Question 11

Which chromosomal alteration involves the reversal of a segment within a chromosome?

Accepted Answer

Inversion

Question 12

Down syndrome is caused by which chromosomal abnormality?

Accepted Answer

Trisomy of chromosome 21

Question 13

Which of the following is true regarding polyploidy in plants and animals?

Accepted Answer

Polyploidy is common in plants but rare in animals.

Question 14

A geneticist observes a female with only one X chromosome (XO). What is the name of this condition and one of its main consequences?

Accepted Answer

Turner syndrome; sterility

Question 15

Which of the following best describes the relationship between gene distance and recombination frequency?

Accepted Answer

The farther apart two genes are, the higher the recombination frequency.

Question 16

A chromosome fragment is moved from one chromosome to a nonhomologous chromosome. This type of chromosomal alteration is called:

Accepted Answer

Translocation

Question 17

Which of the following is a likely outcome of nondisjunction during meiosis?

Accepted Answer

A gamete with two copies of a chromosome

Question 18

A genetic map based on recombination frequencies is called a:

Accepted Answer

Linkage map

Question 19

Which of the following best describes a recombinant type offspring?

Accepted Answer

An offspring with a new combination of traits not found in either parent

Question 20

A woman with genotype $$X^A X^a ($$where $$A is $$dominant and $$a is $$recessive) for an X-linked gene has children with a man with genotype $$X^a Y. $$What is the probability that a son will express the recessive phenotype?

Accepted Answer

$$50\%$$

Chromosomal Basis of Inheritance and Chromosome Alterations

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