Sex determination in mammals and drosophila Flashcards
If an individual has a Y chromosome what sex are they?
Male
If an individual doesnt have a Y chromosome what sex are they?
Female
Which gene on the y chromosome is responsible for “maleness”?
SRY gene
Where is the pseudoautosomal region (PAR)?
On both the x and y chromosome
What is special about the PAR?
It is a region where the X and Y chromosomes have homology
Where can recombination of the x and y chromosome occur?
At the pseudo autosomal regions
How can an XX individual develop into a male?
If unequal crossing over results in the region of the Y chromosome containing the SRY gene being translocated/recombined onto an x chromosome
How can an XY individual develop as a female?
They carry a mutant form of the SRY gene or they lack an androgen receptor
Where, in mice, is the SRY gene expressed?
The developing testes
When is the SRY gene expressed in mouse testes?
11.5 days post fertilisation
What does SRY encode?
A transcription factor
What does the SRY TF have instead of a homeobox?
HMG box/SOX box
Which three regions make up the human SRY TF?
N-terminal, HMG box, C-terminal
Role of the N terminal in human SRY TF?
Enhance DNA binding, Interaction with proteins
Role of the HMG box in human SRY TF?
Responsible for DNA binding, protein-protein interaction, nuclear transportation
Similarity of SRY TF HMG box between humans and mice?
85%
What is the primordium of the gonads?
The genital ridge
How long is the SRY gene expressed for?
Transiently
Which gene does SRY bind upstream of?
SOX9
Which genes is SOX9 involved in regulating?
FGF9 (fibroblast growth factor 9)
Role of FGF9?
It is critical in the development of testis, and can also suppresss WNT4
What does WNT4 suppress?
Ovary development
What does DMRT1 do?
Acts with SOX9 to regulate FGF9 and other genes involved in testis regulation
What are two key cell types present in the testis but not in the ovaries?
Leydig cells and sertoli cells
Which cells secrete testosterone and MIS?
Leydig cells and sertoli cells
What does testosterone and MIS regulate?
The development of male genital characteristics
Which structures does testosterone act on?
Wolffian ducts
What effect does testosterone have on wolffian ducts?
Leads to the differentiation of them into male genital apparatus
What does the MIS act on?
Mullerian ducts
What effect does MIS have on mullerian ducts?
Suppresses their development into female sex characteristics
What happens to the wolffian ducts in the absence of testosterone?
They regress
What happens to the mullarian ducts in the absence of MIS?
They differentiate into female reproductive structures–> fallopian tubes, uterus, upper vagina
What is MIS?
Mullerian inhibitory substance
What happens to the mullerian ducts in the absence of the testis?
They differentiate into female sex organs
Which protein responds to testosterone?
Androgen receptor
What is testicular feminisation?
An individual who has male gonads but lacks an androgen receptor to respond to testosterone
What controls the sex in sexually dimorphic mallams?
The hormones produced by the gonads
Why is one of the x chromosomes inactivated in females?
To prevent a double gene dosage from genes present on that chromosome
