Deck 7: X-Linked Genes and Sex Chromosomes

Question 1

Which of the following statements applies to human females? Please select all that apply.

A) Human females usually have XX chromosomes
B) Human females usually have XY chromosomes
C) Human females are usually homogametic
D) Human females are usually heterogametic

Answer 1

Human females usually have XX chromosomes
Human females are usually homogametic

Question 2

Which of the following factors can impact sex development? Please select all that apply.

A) Mitosis
B) Meiosis
C) Environment
D) Sex chromosomes

Answer 2

Meiosis
Environment
Sex chromosomes

Question 3

In human pedigrees, which characteristics are likely to underlie an inherited trait that appears in males more frequently than in females? Please select all that apply.

A) Trait is recessive
B) Trait is dominant
C) Trait is X-linked
D) Trait is Y-linked

Answer 3

Trait is recessive
Trait is X-linked

Question 4

In meiosis, homologous chromosomes pair and synapse before segregation in meiosis I. How is it possible for the X and Y chromosomes in humans, which are very different, to pair with one another?

A) The chromosomes are the same size
B) Some DNA sequences are found on both the X and Y chromosomes
C) The X and Y chromosomes do not pair during meiosis
D) X pairs with X and Y pairs with Y during meiosis

Question 5

Several steps have been hypothesized for the evolution of sex chromosomes. Put the steps in order, from oldest to newest.

-Acquisition of a sex determining locus

A) 1
B) 2
C) 3
D) 4

Question 6

Several steps have been hypothesized for the evolution of sex chromosomes. Put the steps in order, from oldest to newest.

-Suppression of recombination

A) 1
B) 2
C) 3
D) 4

Question 7

Several steps have been hypothesized for the evolution of sex chromosomes. Put the steps in order, from oldest to newest.

-Sequence degeneration

A) 1
B) 2
C) 3
D) 4

Question 8

Several steps have been hypothesized for the evolution of sex chromosomes. Put the steps in order, from oldest to newest.

-Dosage compensation

A) 1
B) 2
C) 3
D) 4

Question 9

Genetic experiments by Thomas Hunt Morgan and colleagues examined eye color in Drosophila fruit flies. Males are XY and females are XX, and the gene responsible for eye color is on the X chromosome. Red eye color (wild-type) is dominant to white eye color (mutant). The wild type allele is denoted X^w+ and the mutant allele is X^w. Which of the statements about eye color in these fruit flies is true?

A) Half of male flies with X^w have white eyes
B) All female flies with X^w have white eyes
C) Red-eye females can only produce red-eye offspring
D) A cross between red-eye males and red-eye females can produce white-eye males

Question 10

Genetic experiments by Thomas Hunt Morgan and colleagues examined eye color in Drosophila fruit flies. Males are XY and females are XX, and the gene responsible for eye color is on the X chromosome. Red eye color (wild-type) is dominant to white eye color (mutant). The wild type allele is denoted X^w+ and the mutant allele is X^w. Match the missing values in the following sentence:
In a cross between a homozygous female and a red-eye male, [A] of the male offspring will have the same phenotype and [B] of the female offspring will have white eyes. In a cross between a heterozygous female and a white-eye male, [C] of the female offspring will have white eyes and [D] of the offspring will be red-eye males.

Question 11

The opsin genes that encode light receptors are on the Y-chromosome in humans, meaning that red-green color blindness is more likely to occur in males than females.

Question 12

What is holandric inheritance?

A) Where males have an extra Y chromosome
B) Where females have a Y chromosome
C) Inheritance where recessive traits are observed in males more than in females.
D) Inheritance of genes on the Y-chromosome

Question 13

Which of the following leads to gametes receiving incorrect numbers of sex chromosomes?

A) Apoptosis
B) Synapsis
C) Aneuploidy
D) Non-disjunction

Question 14

Genetic experiments by Thomas Hunt Morgan and colleagues examined eye color in Drosophila fruit flies. Males are XY and females are XX, and the gene responsible for eye color is on the X chromosome. Red eye color (wild-type) is dominant to white eye color (mutant). The wild type allele is denoted X^w+ and the mutant allele is X^w.
Rarely, ova receive two X chromosomes or no X chromosomes. Offspring resulting from these ova helped to determine the factors underlying sex determination in Drosophila. In a cross between X^w/X^w and X^w+/Y, which offspring of faulty ova could be distinguished from normal offspring by phenotype alone? Please select all that apply.

A) X^wX^wX^w+ red-eyed female
B) X^wX^wY white-eyed female
C) X^w+O red-eyed male
D) OY

Question 15

Experiments in Drosophila found that XXY flies were female and XO flies were male. This demonstrated that the number of Y chromosomes was critical in determining sex.

Question 16

Gametes can receive incorrect numbers of sex chromosomes during meiosis. Which of the following statements about chromosome segregation are true? Please select all that apply.

A) Failure of chromosome separation is more likely at meiosis I than at meiosis II
B) If chromosome separation fails at meiosis II, all the resultant gametes have an abnormal number of chromosomes.
C) A gamete can receive both X and Y chromosomes only if chromosome separation fails at meiosis I
D) Homogametic gametes are produced when chromosome segregation fails at meiosis II.

Question 17

Experiments in mice found that XY individuals missing a small region of the Y chromosome developed as females. This suggested that the presence of a Y chromosome was critical in determining sex.

Question 18

TDF is the major sex-determining component in mammals. What does TDF do?

A) TDF inactivates one of the X chromosomes
B) TDF encodes SRY on the Y chromosome
C) TDF prevents gene expression from the X chromosome
D) TDF stimulates development of testes

Question 19

Different individuals with additional sex chromosomes display a range of phenotypes. One explanation for this is mosaicism. What leads to mosaicism?

A) Having an extra X chromosome
B) Developmental steps are regulated differently in mosaic individuals
C) Aneuploid cells in the developing embryo.
D) Loss of a chromosome in some cells in the embryo.

Question 20

Most cases of indeterminate sex in humans, i.e., where chromosomal sex does not agree with the development of secondary sex characteristics, are due to the presence of extra sex chromosomes.

Question 21

Some organisms,

A) The sex-determining locus is on the W chromosome
B) Phenotypes resulting from Z-linked genes show up more frequently in males than in females
C) The Z chromosome in birds and the X chromosome in humans are genetically similar
D) The ZW/ZZ and XY/XX systems provide evidence of independent evolution of sex determination.
E) g., birds, have a ZW/ZZ system of sex determination rather than the XY/XX system that is familiar from mammals. Which of the following characteristics are true of the ZW/ZZ system? Please select all that apply.

Question 22

Sex is not always inherited.

Question 23

Match the organism with the most appropriate statement regarding sex determination.

-The male chromosome is smaller than the female chromosome

A) Human
B) Bird
C) Drosophila
D) Turtle

Question 24

Match the organism with the most appropriate statement regarding sex determination.

-Males are homogametic

A) Human
B) Bird
C) Drosophila
D) Turtle

Question 25

Match the organism with the most appropriate statement regarding sex determination.

-Number of X chromosomes determines sex

A) Human
B) Bird
C) Drosophila
D) Turtle

Question 26

Match the organism with the most appropriate statement regarding sex determination.

-Temperature is involved in sex determination

A) Human
B) Bird
C) Drosophila
D) Turtle

Question 27

Which of the following are dosage suppression mechanisms? Please select all that apply.

A) X-inactivation
B) Y overexpression
C) X overexpression
D) RNA inactivation
E) X underexpression

Question 28

Match the missing words in the following phrase. Initially, both X chromosomes in a female embryo have similar expression patterns. During development, one chromosome becomes packed with [A] and is moved to the edge of the [B]. In marsupials, the choice of inactivated X is [C] between cells. In placental mammals, the choice of inactivated X is [D] between cells.

Question 29

Which of the following are true of epigenetic effects? Please select all that apply.

A) The effect is retained in daughter cells
B) The effect is a heritable change in gene activity
C) The effect is a result of changes in the DNA
D) The effect is involved in Y chromosome inactivation

Question 30

Which of the following traits are sex-linked in humans? Please select all that apply.

A) Eye color
B) Hemophilia
C) Colorblindness
D) Testis development

Question 31

Sex determination is an example of canalization.