Sex determination and differentiation

there are often greater differences in behavior between indivuals of the same sex

than between indivuals of the opposite sex

What is sex?

there are several levels of sexuality

what are josts levels of sexuality

chromosomal, gonadal, gametic, hormonal, morphological, behavioral

‘COSTS’ of asexual reproduction

1. pathogenesis vs sexual reproduction

2. Accumulation of deleterious mutations

New zealand snails example

both sexual and parthenogen females occur

• 66 lakes were samples and the frequency of males increased with degree of parasitism in lake population

advantage for the sexual reproducers

what are the two categories of causes of sex differences

intrasexual and intersexual selection

intrasexual selection

access to the opposite sex or resources

intersexual selection

Runaway’ process

Direct benefits

Indirect benefits

Sensory biases

proximate causes of sex differences

• steroid hormones

• activational hypothesis posits

gonad devlop from the

germinal ridge

ovary develops from the

cortex of the germinal ridge

testis devlops froms the

inner medulla of the germinal ridge

direction of determination is

SRY gene

gonadal steroids have

organizing effects on behavior

organizational effects restricted to

partilar time during devlopment

asymmetry exists in

relative effects of testes and ovaries

early hormonal exposure

organizes neural substrates subversing behaviors

later exposure to hormones

activates the sexually differentiated neural substrates

female path of organ development

Mullerian ducts develop while wolffian ducts degenerate

the female path occurs as a

default pathway in mammals

The male path

wolffian ducts devlop while mullerian ducts degenerate

The male path occurs under the influnce of

T and AMH

Development of external genitalia

exists on a single continuum of development in mammals

Male development is due to

androgens and DHT early on

DHT organizes

primordium to male-typical anantomy

DHT production depends on

5a-reductase

Variations of sexual development

turner syndrome and TFM

XO turner syndrome

female pehnotype, but sterile and greater autism prevalence

TFM/AIS

androgen insensitivity syndrome, lack of functional androgen receptors

congential adrenal hyperplasia

overproduction of androgens by fetal gonads masculinizes the phenotype

CAH lacks what enzyme

lack of 21-hydroxylase enzyme leads to overproduction of androgens

In birds females are

heterogametic (ZW)