• Describe the influence of genes on differentiation of the reproductive system.

genes determine everything to do with which way the reproductive system differentiates into whether that be female or male reproductive systems. the determining factor is the SRY gene located on the Y chromosome which itself contains the DT.. gene which if there codes for genes to form testis and go down the male repro system.

interestingly, the genes which actually code for the formation of the male gonads are located on the X chromosomes and so the SRY gene on the Y chromosome is used to utilise these genes on the X chromosome. this is why pathologies such as an induvidual having XX chromosomes but having a male geno and phenotype can occur because on the XX chromosomes somewhere there is a translocation of part of a Y chromosome containing the SRY gene. This can also happen the opposite way round from and a XY chromosome containing induvidual can present as a female due to the fact that the SRY region on the Y chromosome may be defective or deleted causing the female pathway to be initiated.

a good rule of thumb is that if everything stays neutral the female pathway will commence and if androgens are input the male pathway will commence

describe the gonadal differentiation development of males from weeks 4 - 7/8

week 4 = gonadal ridge is formed and the PGCs undergo mitotic division during their migration from the yolk sac to the gonadal ridge, they then enter into the gonadal ridge.

week 5 = primitive sex cords have developed into the testis cords under the influence of the SRY gene

week 7 = Sertoli and leydig cells have been formed which promote further development of the male specific ductal system

• Explain how the gonads initially develop with bipotential

gonads will develop with bipotential until week 7 of development they are known as indifferent gonads until this point.

the path of development from this stage is dependant on the presence or absence of the SRY gene.

before wk 7 th eprocess remains the same

the gonadal ridge is formed from surface endothelial cells and clumps of mesodermal cells.

gonadal ridge is the end zone for primordial germ cells which migrate from the yolk sac to the gonadal ridge, as they migrate they undergo mitotic divisions causing them to multiply. PGCs are required for further gonadal development of the ovaries, if PGCs are not present then the ovary will not properly form and a streak ovary will be formed.