Sex Chromosomes

Question 1

How did XY chromosomes evolve?

Answer 1

Millions of years ago they were identical

X has its genes but Y lost most of its genes

Question 2

What is unique about the Y chromosomes in Drosophila?

Answer 2

It is longer than the X chromosome

Question 3

How is sex determined in Drosophila?

Answer 3

Two sis+ genes = female (2 X chromosomes)

One sis+ gene = male (1 X chromosome)

Question 4

What is unique about meiosis in Drosophila?

Answer 4

Crossovers do not happen in males

Question 5

What is dosage compensation in Drosophila?

Answer 5

Females have twice as many X-linked genes as males so there is an increased X-linked gene expression in males

Question 6

What is a pseudoautosomal region?

Answer 6

A short region of homology in mammalian X and Y chromosomes

Question 7

What is unique about meiosis in mammals?

Answer 7

In males:

on autosomes
at the pseudoautosomal region on sex chromosomes

Question 8

How is sex determined in mammals?

Answer 8

SRY+ gene = male

No SRY+ gene = female

Question 9

What are the steps of sex differentiation in mammals?

Answer 9

1. Gonads in embryo become ovaries or testes depending on the presence of SRY+ gene
2. Ovaries and testes synthesize sex hormones
3. Sex hormones travel to other cells
4. Sex hormones enter cells
5. Sex hormones activate transcription factors that turn on target genes

Question 10

What is the dosage compensation in mammals?

Answer 10

Females have twice as many X-linked genes as males
Decrease X-linked gene expression in females
-turn off all but one X chromosome

Question 11

What is different about germline cells?

Answer 11

Dose compensation functions in all somatic cells but not germline cells