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Exam 7: X-Linked Genes and Sex Chromosomes

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Question 1

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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.

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Question 2

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Sex determination is an example of canalization.

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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.

Match the organism with the most appropriate statement regarding sex determination. -Males are homogametic

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.

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.

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

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

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?

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

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.

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.

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?

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

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

Some organisms,

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.

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

What is holandric inheritance?

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