Question 1

Which of the following best explains why X-linked recessive disorders are more common in males than in females?

Accepted Answer

Males have only one X chromosome, so a single recessive allele will cause the disorder.

Question 2

In the Punnett square shown in the first image, what is the probability that a son will inherit the X-linked recessive trait?

Accepted Answer

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

Question 3

A female cat is heterozygous for fur color (one allele for black, one for orange). Due to X-inactivation, what is the expected phenotype?

Accepted Answer

The cat will have patches of black and orange fur (tortoiseshell).

Question 4

Which process is responsible for the formation of recombinant chromosomes during meiosis?

Accepted Answer

Crossing over between homologous chromosomes

Question 5

If two genes are 17 map units apart, what is their expected recombination frequency?

Accepted Answer

$$17\%$$

Question 6

A testcross between a dihybrid fruit fly (b+ vg+/b vg) and a double mutant (b vg/b vg) produces mostly parental-type offspring and fewer recombinant offspring. What does this indicate about the genes?

Accepted Answer

The genes are linked and located close together on the same chromosome.

Question 7

Which chromosomal abnormality is illustrated by the presence of three copies of chromosome 21 in a human karyotype?

Accepted Answer

Trisomy (Down syndrome)

Question 8

Which of the following best describes the function of the XIST gene in female mammals?

Accepted Answer

It produces an RNA transcript that coats and inactivates one X chromosome.

Question 9

A chromosome segment is reversed end to end. What type of chromosomal mutation is this?

Accepted Answer

Inversion

Question 10

If nondisjunction occurs during meiosis II in a human oocyte, what is the possible chromosomal composition of the resulting gametes?

Accepted Answer

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

Question 11

Which of the following statements about genetic linkage is correct?

Accepted Answer

Linked genes tend to be inherited together because they are located close to each other on the same chromosome.

Question 12

A male with an X-linked recessive disorder and a female carrier have a daughter. What is the probability that the daughter will express the disorder?

Accepted Answer

$$50\%$$

Question 13

Which of the following best explains why the maximum recombination frequency between two genes is $$50\%$$?

Accepted Answer

Genes that are far apart on the same chromosome or on different chromosomes assort independently.

Question 14

Which chromosomal alteration is most likely to result in a fusion gene that can cause cancer, such as in chronic myelogenous leukemia?

Accepted Answer

Reciprocal translocation

Question 15

A plant species has a chromosome number of $$2n=14. A $$polyploid individual is found with $$4n=28. $$What type of chromosomal alteration is this?

Accepted Answer

Polyploidy

Question 16

Which of the following is a direct consequence of random X chromosome inactivation in female mammals?

Accepted Answer

Mosaic expression of X-linked genes

Question 17

If a chromosome undergoes a deletion, what is the most likely result?

Accepted Answer

Loss of genetic material and possible genetic disorders

Question 18

Which of the following best describes the relationship between Mendel’s law of independent assortment and chromosome behavior during meiosis?

Accepted Answer

Homologous chromosome pairs align and separate independently during meiosis I.

Question 19

A geneticist observes that two genes have a recombination frequency of $$9.5\%. $$What does this indicate about their physical relationship?

Accepted Answer

They are relatively close together on the same chromosome.

Question 20

Which of the following is NOT a possible result of nondisjunction during meiosis?

Accepted Answer

Production of gametes with only autosomes and no sex chromosomes

The Chromosomal Basis of Inheritance

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