lecture 7 Flashcards
what is the structure of the male Y chromosome?
It consists of two parts: the MSY (male-specific region of the Y) and the PAR (pseudoautosomal region)
The PAR is at both ends of the Y chromosome and the MSY is in the middle.
The MSY encodes for 27 proteins and it contains 78 genes
The PAR is the only region of the Y chromosome that can recombinate. It shares homology with regions on the X chromosome and it can recombine with it during meiosis. it is critical for X and Y chromosome segregation.
what is DOSAGE COMPENSATION?
Dosage compensation is performed by organisms to balance the dose of X chromosome gene expression in females and males. It ensures that the level of transcription of genes from the X chromosome is the same in both females and males, even though females have one more X chromosome.
what is the process that allows dosage compensation in humans?
it is called X chromosome inactivation = a random process in which either the paternal or the maternal X chromosome (in each cell of the embryo) gets inactivated, resulting in the formation of a Barr body.
what are the sex chromosomes?
Testosteron and estrogen
testosterone is made from cholesterol and it is changed by an enzyme called 5lpha-reductase into Dihydro-testosterone, that is responsible for sex characteristics in males
it is turned by aromatase into estrogen (= female hormone)
how is sex in drosophila determined?
it is basically determined by the ratio between X chromosomes and the ratio of autosomes.
but also, there is another very important mechanism:
if there are 2 X chromosomes present in a Drosophila, then this leads to production of a protein Sex-lethal that acts as a splicer. If the Sxl protein splices out exon 3, then the fly will be a female. exons 2-3-4: male
this works as a stable binary genetic switch: Sxl is activated and it produces a downstream splicing cascade of several transducers of the sexual state.
