Chapter 12.4.2 (Exam 3) Sex Chromosomes

Question 1

What determines the sex of mammals?

Answer 1

Females → two X chromosomes (XX)

Males → one X and one Y (XY)

Question 2

How many different types of mammalian gametes does the female produce? Male?

Answer 2

Female mammals have one kind of gamete that carries an X

Male mammals produce two kinds of gametes—half carry a Y and half carry an X

Question 3

What does the sex of mammalian offspring depend on?

Answer 3

Which male gamete fertilizes the egg (X or Y)

Question 4

What results from nondisjunction?

Answer 4

Sex chromosome abnormalities

Question 5

Where can nondisjunction occur?

Answer 5

Homologous chromosomes fail to separate in anaphase I

Sister chromatids fail to separate in anaphase II

Result is aneuploidy—abnormal number of chromosomes

Question 6

In humans, abnormalities helped pinpoint the gene that determines sex. What are two examples of this?

Answer 6

XO—Turner syndrome; only one sex chromosome; female, sterile

XXY—Klinefelter syndrome; affects males; sterility and overlong limbs

Suggests gene for maleness is on the Y chromosome

Question 7

What is the evidence for the Y chromosome containing the SRY (sex-determining region on the Y chromosome)?

Answer 7

XY females and XX males