Sexual Differentiation

Question 1

Define sexual determination

Answer 1

Genetically controlled process, dependent in the ‘switch’ on the Y chromosome (chromosomal determination of male or female).

Question 2

Define sexual differentiation

Answer 2

The process by which internal and external genitalia develop as male or female.

Question 3

Gonadal sex dev. explained (3)

Answer 3

SRY gene created the testis (in absence of Y chromosome, ovaries develop)

SRY switches on briefly during embryo dev. (>week 7) = gonad made into a testis (In absence, ovary is formed)

Products of testis (AMH, Testosterone) influence further gonadal and phenotypic sexual development.

Question 4

What hormones do the testis produce?

Answer 4

Anti-Müllerian hormone(AMH) - Sertoli cells
Testosterone - Leydig cells

Question 5

Mechanisms of SRY action (5)

Answer 5

SRY = DNA binding protein -> acts as a TF

Critical site of DNA binding is upstream of SOX9 (TF)

SOX9 works through a +tive feedback mechanism, it binds to its own upstream activation (= levels remain high, even if SRY declines)

SOX9 then acts to stim. expression of further downstream genes.

Becomes a Sertoli cell: SRY determines executive policy and SOX9 implements it

Question 6

How does SOX9 achieve its effects?

Answer 6

1) stim. PGD2 production(pre-Sertoli cells) = acts as a paracrine hormone to stim. more SOX9 production in these cells! 2nd +tive feedback mechanism to re-inforce all precursors along Sertoli pathway.

2) stim. production of FGF9 = acts as chemotactic factor for cell migration in dev. testis, + further stim. production of SOX9! 3rd +tive feedback mechanism

3) stim. AMH production = regression of Müllerian ducts

4) inhibition of female TF’s WNT4 + FOXL2

Question 7

Gonadal development - both (2)

Answer 7

After fertilisation, a pair of gonads develop, which are BIPOTENTIAL

Their precursor is derived from Genital Ridge Primordial(common somatic mesenchymal tissue precursors) - 3.5/4.5 wks! This is on posterior wall of lower thoracic lumbar region.

Question 8

what 3 cell waves invade the Genital Ridge? (3)

Answer 8

3 waves of cells invade the genital ridge…

1. Primordial Germ Cells – become Sperm (male) or Oocytes (female).
2. Primitive Sex Cords – become Sertoli cells (male) or Granulosa cells (female).
3. Mesonephric Cells – become blood vessels and Leydig cells (male) or Theca cells (female).

Question 9

1) Primordial Germ Cell Migration

Answer 9

Initially: A small cluster of cells in the epithelium of yolk sac expands (by mitosis) @ around 3wks.

They then migrate to connective tissue of the hind gut -> the region of the dev. kidney -> onto genital ridge ~ completed by 6wks

Question 10

2) Primitive sex cords (Sertoli/granulosa)

Answer 10

Cells from germinal epithelium (that overlies the genital ridge mesenchyme) migrate inwards as columns called primitive sex cords.

Picture

Question 11

3) Mesonephric cells -men and women

Answer 11

Original in the mesonephric primordium (lateral to the genital ridges)

In males: act under influence of pre-Sertoli cells (which express SRY) to form:
Vascular tissue
Leydig cells ~ synthesise testo., don’t express SRY
Basement membrane ~ contribute to formation of seminiferous tubules + rete-testis

In females: w/o influence of SRY they form:
Vascular tissue
Theca cells

Question 12

Gonadal sex summary

Answer 12

Images

Question 13

Internal Reproductive Organs - all men are …, women are in the…(2)

Answer 13

Müllerian ducts:
Most important in female
Inhibited in male by AMH

Wolffish ducts:
Most important in the male stim. by testo.
Lack of stim. by testo. means regression in female

Question 14

Internal sex differentiation

Answer 14

8mages

Question 15

5-a-reductase - men AND NOT women (3)

Answer 15

Testo. converted to DHT by 5-a-reductase (in genital skin)

DHT binds to testo. receptor (more potent)

DHT causes: (differentiation of male external genitalia)
Clitoral area enlarges = penis
Labia fuse and become ruggated = scrotum
Prostate forms

Question 16

External differentiation

Answer 16

Images

Question 17

Sex Differentiation summary

Answer 17

Image

Question 18

Sex definition

Answer 18

Biological aspects of an individual as determined by their anatomy, which is produced by their chromosomes and hormones etc.

Question 19

Gender definition

Answer 19

A social construct relating to behaviours and attributes based on labels of masculinity and femininity

Question 20

Gender identity

Answer 20

The personal, internal perception of oneself.
(Man, woman, no gender, non-binary)

Question 21

Gender role

Answer 21

Expression/portrayal of psychological characteristics that are considered sexually dimorphism within the general population
(E.g. toy preferences, aggression etc.)

Question 22

Sexual orientation

Answer 22

Preference if sexual partner and erotic interest
(Heterosexual, homosexual, bisexual)

Question 23

Psychosexual neutrality

Answer 23

The view that gender assignment of a newborn with ambiguous genitalia can be made regardless of the endocrine history.

Question 24

Neural bias

Answer 24

The idea that a tendency for male or female is already present in neonates as a result of prenatal factors, such as the hormone milieu in utero

Question 25

Hormones and behaviour displayed by 3 animal studies

Answer 25

Exposing animals to sex hormones during a critical period before or just after birth is associated with sexually divergent behaviour.

Androgens may influence dev. of these behavioural differences by acting on structure of dev. brain.

1) dog breeder wait until dogs learn to cock their leg before neutering. Neutered early = never develop this behaviour

2) female mice treated with testo. in first 5 days of life = increases their display of masculine sexual behaviour in adulthood + decreases female patterns

3) castration if males rats during this period = removes influence of androgens and has reverse effect

Question 26

is there a gender difference in brain? (3)

Answer 26

No. of genes differentially expressed in male and female embryonic brains

Both morphological + functional differences in human brain structure according to sex have been described

Neuroimaging has shown functional sex differences in a variety if brain regions in activists related to:
Emotion, memory, learning, language, olfaction, vision, hearing, navigating, processing of faces and pain perception

Question 27

Gender differences pt 2 (morphological - 2 specific locations in brain) (4)

Answer 27

Larger amygdala in males? (Involved with emotional processing ~ size is positively correlated w/ aggressive behaviour across species)

Left amygdala more active in women? (associated with emotional memories)

Hippocampus contains more grey matter in female? (involved in memory & social cognition)

HOT TOPIC : 3rd interstitial nucleus of anterior hypothalamus (INAH-3) has been suggested as a major determinant of sexual identity. May be larger in heterosexual males than in homosexual males + heterosexual females.

Question 28

Does gender assignment at birth tend to reinforce some developing behaviours and not others? - studies of adults + babies (2)

Answer 28

When adults are handed a baby + told sex = their play + communication differ according to their perception of its sex.

In a study: adults watched a film of child play (half were told both and half were told girl), when the child was startled = boy thought it was angry, girl thought it as sign of distress

Question 29

Social learning study 2-6yrs olds(4)

Answer 29

By 2: children consistently label themselves as male or female

By 5: they appear to have a sense of gender constancy (believe gender cannot be changed)

3-6 yr olds shown a video: description of children playing different according to whether it’s a boy or girl = appear more rigidly gender stereotyping than adults performing the same task.

= supports view that gender stereotypes are applied to babies + children themselves use + apply them from an early age

Question 30

Sex and gender summary (4)

Answer 30

Some gendered patterns of behaviour may be induced by the way boys and girls are treated or as a result of the expectations of others.

Differentiation of the human brain is partly due the hormonal environment in utero and/or neonatally.

Even before foetal hormone levels rise there are numerous genes expressed differently in male and female brains.

Psychosexual development is not fully understood and remains the focus of active research and investigation.