Question 1

Which of the following best explains how the behavior of chromosomes during meiosis supports Mendel’s law of independent assortment?

Accepted Answer

Homologous chromosomes pair and then segregate independently during meiosis I, resulting in random combinations of maternal and paternal chromosomes in gametes.

Question 2

In Morgan’s experiments with Drosophila melanogaster, what observation led to the conclusion that genes are located on chromosomes?

Accepted Answer

The inheritance of eye color was correlated with the sex of the offspring, suggesting the gene was on the X chromosome.

Question 3

A woman who is heterozygous for an X-linked recessive disorder has children with a man who does not have the disorder. What is the probability that their son will have the disorder?

Accepted Answer

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

Question 4

Which of the following best describes a genetic map?

Accepted Answer

A diagram showing the relative positions of genes on a chromosome based on recombination frequencies.

Question 5

If two genes are located very close together on the same chromosome, which of the following is most likely true?

Accepted Answer

They will be inherited together more often than not due to low recombination frequency.

Question 6

A geneticist observes that two genes have a recombination frequency of 12%. What does this indicate about their physical relationship?

Accepted Answer

The genes are relatively close together on the same chromosome.

Question 7

Which chromosomal abnormality is characterized by the presence of three copies of chromosome 21?

Accepted Answer

Trisomy 21 (Down syndrome)

Question 8

Which process can result in an individual with an abnormal number of chromosomes, such as trisomy or monosomy?

Accepted Answer

Nondisjunction during meiosis

Question 9

A female mammal is heterozygous for an X-linked gene. What phenomenon ensures that only one allele is expressed in each cell?

Accepted Answer

X inactivation, resulting in the formation of a Barr body

Question 10

Which of the following best describes aneuploidy?

Accepted Answer

A condition in which an organism has an abnormal number of chromosomes, such as trisomy or monosomy.

Question 11

If a crossover occurs between two genes that are 20 map units apart, what percentage of gametes are expected to be recombinant for these genes?

Accepted Answer

$$20\%$$

Question 12

Which chromosomal change is most likely to result in a gene being expressed inappropriately due to its relocation to a new chromosomal environment?

Accepted Answer

Translocation

Question 13

A child is born with Turner syndrome. Which of the following karyotypes would you expect to find?

Accepted Answer

$$45,\;X$$

Question 14

Which of the following is a direct consequence of crossing over during meiosis?

Accepted Answer

Increased genetic variation among gametes

Question 15

A plant species is found to have four sets of chromosomes in each cell. What is this condition called?

Accepted Answer

Polyploidy

Question 16

Which of the following best explains why linked genes do not always show perfect linkage?

Accepted Answer

Crossing over can occur between homologous chromosomes, separating linked genes.

Question 17

A geneticist is mapping two genes and finds a recombination frequency of 50%. What does this suggest about the genes’ locations?

Accepted Answer

They are either on different chromosomes or far apart on the same chromosome.

Question 18

Which chromosomal event is most likely to result in a genetic disorder such as cri du chat syndrome?

Accepted Answer

A deletion of a segment of chromosome 5

Question 19

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

Accepted Answer

Females are genetic mosaics for X-linked genes.

Question 20

A woman with normal chromosomes has a child with Down syndrome. Which meiotic error most likely occurred?

Accepted Answer

Nondisjunction during meiosis I or II in the mother

L15: Chromosomal Basis of Inheritance

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