Prenatal Sexual Development

Why would psychologists be concerned with physical development, especially prenatally?

1. Sex is a powerful determinant and predictor of behavior 2. Prenatal events determine physical sex and influence psychosexual behavior

Sex Hormones: Misconceptions Females have only “female” hormones called estrogens. Males have only “male” hormones called androgens.

Most sex hormones are produced by both males and females… Just in different quantities

“Female” hormones Estradiol (an estrogen) Progesterone

“Male” hormones Androgens: testosterone dihydrotestosterone (DHT) androstenedione

“Male” hormones Anti-Mullerian Hormone (AMH) Mullerian Inhibiting Hormone (MIH) Mullerian Inhibiting Substance (MIS) AMH is found only in males

Differentiating Body Parts Prenatal Development Differentiating Body Parts Gonads (testes & ovaries) Internal sex organs External sex organs

The Eve Principle Without the prenatal influence of sex hormones, a fetus will develop as a female regardless of its chromosomes

In the beginning . . . XX chromosomes XY chromosomes

Gonads: Testes and Ovaries Primordial gonads Not differentiated into male or female

Gonads: Testes and Ovaries SRY gene on the Y chromosome directs the primordial gonads to make Sry protein

Gonads: Testes and Ovaries Sry protein aka Testes Determining Factor aka HY antigen testes

XX chromosomes create ovaries XY chromosomes create testes testosterone Mullerian Inhibiting Hormone (MIH)

Internal Sex Organs: e.g., seminal vesicles (male) and uterus (female) Two precursor systems are present in all fetuses

male female Internal sex organs The Mullerian System Needs no hormones to develop If MIH, it degenerates The Wolffian System Testosterone to develop or else it degenerates

female male

Precursor potentially male or female, like the Primordial Gonads External Sex Organs: ~ 2-3 months gestational age Precursor potentially male or female, like the Primordial Gonads

male female External sex organs Masculinized by DHT (dihydro-testosterone) not testosterone per se No hormones needed to develop

male female

Differentiating the Brain Prenatal Development Differentiating the Brain Hypothalamus

No hormones leads to: Female brain that releases hormones in monthly cycles (after puberty) Perhaps influences sexual preference

With Hormones Male brain that releases hormones steadily (after puberty) Probably influences male behaviors (e.g., aggression) Perhaps influences sexual preference

No SRY gene

SRY gene T?

Strange but predictable anomalies…

What would happen if an XY fetus had no receptors for androgens (MIH worked fine)? Androgen Insensitivity Disorder May be partial or full insensitivity Genetically male, female external genitalia, but no internal sex organs (i.e., no menstruation, infertile), little body hair; likely to identify as female.

What would happen if an XX fetus was exposed to androgens after the internal sex organs had developed? Female internal reproductive system, masculinized external genitalia.

Prader scores in 46XX disorders of sexual development Prader scores in 46XX disorders of sexual development. Early feminizing genitoplasty is standard of care for Prader score > 3.