ICSI:
III. Sex Determination
A. Temperature: in some Reptiles.
B. Chromosomes
1. Usually
♀= XX
2. abnormalities XO= ♀
♂ = XY
XXY = ♂
3. Presence of ____Y_______ = ______ ♂ _________
– Y Carries gene  proteins determine maleness
4. Early embryo (7wks)
a.
Undifferentiated gonads + both ♂ + ♀ ducts (Wolffian +
Mullerian)
b. Sex-Determining region of Y (SRY): Tells gonads to become
____Testes_____
c.
Testes:
i.
Produce Mullerian Inhibiting Hormone (MIH) to
___Degenerate Mullerian Tubes_________________
ii.
Produce testosterone to turn ___Wolffian Tubes____
into vas deferens, seminal vesicles and epididymis.
C. Hormones determine Phenotypes
• Testosterone converted to Dihydrotestosterone (DHT)
to make external genitals.
D. Mutations: Chromosome Sex vs Phenotypic sex
-many scenarios, here are three
1. Hermaphrodites: have both both testes and ovaries
a.
Sex c-some mosaics: some cells _XX some XY or XXY
2. Androgen insensitivity: XY with female phenotype
a.
b.
Mutation found on androgen receptor (AR) gene of X
chromosome.
i.
The normal gene responds to testosterone and DHT to
make a male
ii. The mutant gene is insensitive to those hormones, so
female developes.
Results in a wide range of phenotypes usually infertile ♀
(Joan of Arc)
3. Pseudohermaphroditism: XY appears female till
puberty than becomes male
a.
b.
Pre-Puberty: Male gonads start to form, but DHT not made,
so genitalia appear female.
Puberty:
i.
Increased levels of testosterone cause testes to move
down and scrotum to develop.
ii.
Clitoris develops into a penis. Everything is functional.
E. Equalizing X c-some in ♀ (Why don’t X gene
proteins show up twice as often females)
1. ♀ has XX but same amount of gene production as ♂
w/ one X
2. Barr 1949 noticed a dark body in nucleus of ♀ cells.
a. Barr Body: Tightly coiled inactivated X
i. Happens early in development. Random Paternal
or Maternal X
ii. All descendent cells have the same X inactivated.
iii. Permanent except in germ cells.
3. ♀ can be mosaics
a.
b.
some cells express Maternal traits, some Paternal traits
Tortoiseshell cat
i.
Calico cat: wh. Gene on autosome. All ♀
4. Process not well understood
a.
X becomes coated with RNA, coiled and inactivated
5. Timing: At about 32 cell stage: blastocyst
a.
Random: sometimes mostly maternal + sometimes
Paternal.
b.
Identical twin may express different x-linked trait (like color
blindness)
F. Unusual Trait Inheritance
1. Sex-influenced genes: hormones affect gene
expression
a.
Patterned Baldness: Dominant in ♂ needs: only 1 gene
i.
Recessive in ♀ needs 2 genes
ii. Testosterone in males increases expression.
2. Sex-limited genes: expressed in only one sex
a.
b.
Facial hair
Milk production