Chapter 15.2

Question 1

The __ chromosome is much smaller than the ___ chromosome.

Answer 1

Y, X

Question 2

A person who inherits two X chromosomes usually develops as a _________

Answer 2

Female

Question 3

A male inherits ________

Answer 3

One X chromosome and one Y chromosome.

Question 4

Short segments at either end of the Y chromosome are the only regions that are homologous with regions of the X. These homologous regions allow the X and Y chromosomes in males to pair and behave like homologs during meiosis in the testes.

Answer 4

True

Question 5

Half the sperm cells a male produces receive an X chromosome, and half receive a Y chromosome.

Answer 5

True

Question 6

Sex-linked gene

Answer 6

A gene located on either sex chromosome.

Question 7

Y-linked genes

Answer 7

Genes located on the Y chromosome.

Question 8

X-linked genes

Answer 8

Genes located on the X chromosome. Contains approximately 1,100 genes.

Question 9

While most Y-linked genes help determine sex, the X chromosomes have genes for many characters unrelated to sex.

Answer 9

True

Question 10

Fathers pass X-linked alleles to all of their daughters but to none of their sons. In contrast, mothers can pass X-linked alleles to both sons and daughters.

Answer 10

True

Question 11

Because males have only one locus for an X-linked trait, the terms homozygous and heterozygous lack meaning; the term_______ is used in such cases. For this reason, far more males than females have X-linked recessive disorders.

Answer 11

Hemizygous

Question 12

Duchenne muscular dystrophy

Answer 12

An X-linked disorder, which affects one out of 3,500 males born in the US.

Question 13

Hemophilia

Answer 13

An X-linked recessive disorder defined by the absence of one or more of the proteins required for blood clotting.

Question 14

Almost all of one X chromosome in each cell in female mammals becomes inactivated during early embryonic development.

Answer 14

True

Question 15

The inactive cell of a female condenses into a compact object called a _____

Answer 15

Barr body

Question 16

Females consist of a mosaic of two types of cells: those with the active X derived from the father and those with the active X derived from the mother. After an X chromosome is inactivated in a particular cell, all mitosis descendants of that cell have the same inactive X. Thus, if a female is heterozygous for a sex linked trait, about half her cells will express one allele, while the others will express the alternate allele.

Answer 16

True