Lecture 35 Flashcards
What is a typical female and typical male chromosomes?
female: XX
male: XY
Describe the sex spectrum
There is the typical male and typical female as well as reduced congruence between physiological aspects of biological sex (may be subtle differences in anatomy)
How can there be bimodal distribution of traits?
The two typical mammalian biological sex phenotypes are associated with antagonistic networks of gene expression with two stable states.
Initially, neither one of these networks are going, but then when one network (ex: female associated) is active, there is a positive feedback that causes amp up of one network and turn down the other (male network)
What is the most important upstream gene that causes the process to start?
SRY- which is associated with the male typical development
What happens to the bipotential gonad if there is high SRY expression vs low?
1.) initially in early development, you have a bipotential gonad (can develop into testes or ovaries)
2.) if there is SRY expression= male typical genes get expressed
3.) triggers cells to differentiate and develop into male phenotype
4.) After expression of those genes in the gonad, the gonad develops into testes
(Low SRY expression causes the female typical genes to get expressed, then the cells differentiate to the female phenotype, leading the gonad to develop into ovaries
What happens after cells differentiate (after the high/low SRY expression)
Differentiated gonads (testes vs ovaries) then control the much of the remainder of sex-specific development in mammals by secreting hormones: sex steroids and (in males) anti- Mullerian hormone
What are sex hormones derived from?
Cholesterol
- we all produce the same hormones, but in different amounts
Which two sex steroids are highly expressed in females?
Estrogen and progesterone
Which sex steroids are highly expressed in males physiology ?
Androgens (testosterone, DHT)
Anti-Mullerian hormone (expressed by testes)
Female typical development
- XX chromosomes
- No SRY gene
- Primordial gonads differentiation into fetal ovaries
- Absence of AMH and testosterone
- Lack of AMH means that the mullerian tissues will develop (transformation to uterus, fallopian tubes, and inner vagina)
- Lack of testosterone= no development of male typical external genitalia (no penis)
-Lack of testosterone will later lead to development of outer vagina and female external genitalias
Male typical development
- XY chromosome
- Presence of SRY gene (on Y chromosome)
- Primordial gonads differentiation into fetal testes
- Testes secrete a lot of AMH (mullerian tissues don’t develop)
- Testosterone (androgens) trigger the development of male typical external genitalia
- After puberty, high androgens will lead to the development of male secondary sexual characteristics
Why is the female default model incomplete?
XO female humans with Turner syndrome (haploid sex chromosome)
- Almost always infertile
What are some mechanisms that can lead to physiological differences in “typical male” and “typical female”
- Allelic variation between individuals (transcription factors, enzymes, hormones, hormone receptors can be different)
What is CAIS
Person with XY chromosomes, but androgen receptors don’t work
- Person looks very feminine, but have a penis
-very rare
What did people believe about Hysteria?
People can be hysterical because their uterus is doing something
- leading to anxiety, insomnia, depression… (a phycological disorder)
- something that females have but males don’t have (later believed to be link to the nervous system and not the uterus)
