Sex differences in behaviour 2

lesson 2

what are they key dimensions of sex?

• whom one is attracted to

• self identification as man, woman or non- binary

• chromosomal sex (XX or XY)

• appearance of external genitalia (male, female, intersex)

what’s sexual differentation?

Sexual differentiation is the biological process of becoming male or female, starting at fertilization with chromosomal sex determination, leading to gonadal, morphological, and hormonal differentiation, which then affects behavioral sex differences.

what’s the pathway of sexual differentiation from chromosomal sex to behavioural sex differences?

1. chromosomal sex (XX or XY)

2. gonadal sex (ovaries or testes)

3. morphological sex (body type)

4. hormonal sex (steroid hormone concentrations) these lead to behavioural sex differences later.

What happens at 6-7 weeks of fetal development in sexual differentiation?

The germinal ridge (on the protokidney) begins to develop into gonads. The default development is female, with the germinal ridge becoming an ovary.

How does the SRY gene influence sexual differentiation?

The SRY gene on the Y chromosome triggers the production of TDF (Testis Determining Factor), leading to the formation of testes and male sexual differentiation.

What happens if SRY is mutated or transposed?

• mutation in SRY (e.g., Swyer syndrome) can result in XY individuals with streak gonads and female genitalia.

• If SRY is transposed to an X chromosome, an XX individual may develop testes and male genitalia (46, XX testicular disorder of sex development).

what’s the role of gonads in sexual differentiation?

Gonads (testes or ovaries) are initially determined by genetics (chromosomal sex), and after that, hormones produced by the gonads influence further sexual differentiation

What are the Mullerian and Wolffian duct systems?

• Müllerian duct system: Female sex organs (fallopian tubes, uterus, cervix).

• Wolffian duct system: Male sex organs (vas deferens, seminal vesicles).

• Both systems are present in embryos until about 6 weeks of development.

how do testes and ovaries influence sexual development?

• Testes produce androgens (e.g., testosterone) and Müllerian Inhibitory Hormone (MIH), guiding male development.

• Ovaries do not produce high levels of hormones initially, so the absence of androgens allows female development.

what’s androgen insensitivity syndrome?

AIS is a condition where the androgen receptor gene is mutated, causing XY individuals to develop female external genitalia despite having male chromosomes (XY, undescended testes).