Sex and the Single Chromosome Flashcards
1
Q
What are autosomes?
A
Have nothing to do with sex
2
Q
What chromosomes do females have?
A
- 22 pairs of autosomes and XX
- All gametes 22A + X
- Homogametic
3
Q
What chromosomes do males have?
A
- 22 pairs of autosomes and XY
- Half gametes 22A + X and half 22A + Y
- Heterogametic
4
Q
Why do sex ratios balance out?
A
- Rare sex has an evolutionary advantage to get genes into the next generation
- Ratio balances back out
5
Q
What are four human chromosome abnormalities?
A
- 44AOY: Dies
- 44AXO: Turner’s syndrome
- 44AXXY: Klinefelter’s syndrome
- 44AXXX: Triple X
- 44AXYY: Double Y
6
Q
What is Turner’s syndrome?
A
- Female phenotype
- Sterile
- Late sexual maturity
- Webbing of skin on neck
- Upturned fingernails
7
Q
What is Klinefelter’s syndrome?
A
- Variable male phenotype
- Sterile
8
Q
What is triple X?
A
- Normal female phenotype
9
Q
What is double Y?
A
- Normal male phenotype
10
Q
How is sex determined?
A
- By the Sex Determining Region (SRY) gene
- Default development is female
11
Q
What is required for males?
A
- Testis determining factor: SRY locus on Y chromosome
- Receptor for male steroid hormones: androgen receptor on X chromosome
12
Q
What genes are involved in sex linkage?
A
Genes on the part of X and Y chromosomes that do not pair
13
Q
Why is sex disadvantageous?
A
Two-fold cost of sex
- Female that has only females will get more genes into the next generation
- Sexual female will have half children who may not pass on her genes directly
Require a mate
- Look for mates
- Compete for mates
- Finding mates at low population density
14
Q
What is anisogamy?
A
Difference in the size of eggs and sperm
15
Q
Why is anisogamy important?
A
- Large gametes: more food and more robust
- Small gametes: can produce more of them
- Intermediate size has no advantage
- Outcome is evolutionary arms race
