Lecture 6

Question 1

sex determination by environment

Answer 1

not determined at conception
eg. sea worm (secretion of chemical switching maleness)
reptiles influenced by temperature of eggs

Question 2

sex determined by genes

Answer 2

particular genotype may change the expected sexual phenotype. may be altered after conception

eg. Drosphila (tra locus can reverse the sex of a female as in, tra is needed to continue making it a female)
eg. Disorder of sexual development (DSD) Androgen receptors insensitivity

Question 3

sex determined by Haplo/diploidy

Answer 3

if the egg is fertilised or not
determined at conception
eg. bees some become males and some become females

Question 4

sex determined by balance of autosomes to sex chromosomes

Answer 4

determined by a ratio

Dros female X/A ratio =1 (AAXX), male X/A ratio of 1/2 (AAX) is a male but need Y to be fertile determined at conception

Question 5

sex determined by a sex chromosome

Answer 5

determined at conception

result of not having a Y is femaleness

Question 6

In humans, what is the Y responsible for?

Answer 6

producing the testes, making a male, male

Question 7

X - monoploidy (turner’s syndrome)

Answer 7

• female phenotype
• ovaries and uterus underdeveloped
• Don’t go through puberty
• Both sex chrom. needed for normal development

Question 8

XXY Klinefelter

Answer 8

• male phenotype

- some infertile, learning difficulty, reduced genitalia, breast development

Question 9

Heterogametic vs homogametic

Answer 9

males are heterogametic: two types of gametes X and Y

in the case that females are heterogametic, Z and W

Question 10

If a female is XX and male is XY

Answer 10

females can be XCXC
XCXc
XcXc
males can only be XCY or XcY = hemizygous

Question 11

How to figure out if something is autosomal or sex linked

Answer 11

Two crosses:
Reciprocal cross –> female A phen x male B phen
to female B phen x male A phen
crosses will have different outcomes if the gene is on a sex chromosome