Talk:ANAT2341 Lab 1 - Fertilization

Archive: 2015 page

Sex Determination

Mammalian sex determination is regulated by chromosomes.

• Females have two X chromosomes. (XX)
• Males have a single X and a small Y. (XY)
• The X and Y chromosome are morphologically and functionally different from each other.
• Evolutionary studies have shown that the Y was once the homologous pair for X.
• It is only in the last 5 years that we have some idea about how these two types of chromosomes may be regulated and genes of importance located upon them.

X chromosome

In females - the main scientific problem was understanding gene dosage, only one copy of X chromosome is needed to be genetically active the other copy is inactivated (More? X Inactivation. About the X Chromosome 155 million base pairs In contrast to the Y chromosome, the X chromosome contains about 5% of the haploid genome and encodes house-keeping and specialized functions. Genes such as Wnt-4 and DAX-1 necessary for initiation of female pathway ovary development An early discovery (1961) was that in order to have correct levels of X chromosome gene/protein expression (gene dosage), females must "inactivate" a single copy of the X chromosome in each and every cell. The initiator of the X inactivation process was discovered (1991) to be regulated by a region on the inactivating X chromosome encoding an X inactive specific transcript (XIST), that acts as RNA and does not encode a protein. The genetic content of the X chromosome has been strongly conserved between species because these genes have become adapted to working as a single dose - Ohno's law X inactivation occurs randomly throughout the embryo, generating a mosaic of maternal and paternally derived X chromosome activity in all tissues and organs. This can be seen in the fur colour of tortoiseshell cats.

Y chromosome

In males - the main scientific problem was understanding what on the Y chromosome determined "maleness", and how this is done. About the Y Chromosome 59 million base pairs, hypervariable in length, mostly non-functional repeats Current known protein-coding genes = 48 including SRY SRY encodes a 204 amino acid protein that is a member of the HMG (High mobility group) box class of DNA-binding proteins. Transcription factors bind to specific sites of DNA and regulates the transcription (expression) of other genes.