| MadSci Network: Genetics |
Hello, The X and Y chromosomes diverged around 300 million years ago from a pair of identical chromosomes [Lahn B et al, 1999] called autosomes, when an ancestral mammal developed an allelic variation, a so-called 'sex locus' - simply possessing this allele caused the organism to be a male [Graves J.A.M.,2006]. The chromosome with this allele became the Y chromosome, while the other member of the pair became the X chromosome. Over time, genes which were beneficial for males and harmful to (or had no effect on) females either developed on the Y chromosome, or were acquired through the process of translocation.[Graves J.A.M.,2006] The Human Y chromosome spans 58 million base pairs and represents approximately 0.38% of the total DNA in a human cell. It contains 78 genes, which code for only 23 distinct proteins. while there are close to 1000 working genes on the X chromosome. In 2003, researchers from MIT discovered that human Y chromosome is able to "recombine" with itself, using palindromic base pair sequences[Rozen S et al, 2003] which contain functioning genes important for male fertility. About 56, or 72%, of the Y chromosome genes are in pseudoautosomal regions at the telomeres and these genes are common between both the sex chromosomes. The Y chromosome is one of the sex-determining chromosomes in humans and most other mammals. In mammals, it contains the gene SRY, which triggers testis development, thus determining the gender. So, there are quite of lot of significant differences in X and Y chromosomes functionality as well as morphologically e.g. In terms of Base pair sequences, Size etc. If you have any more queries, Kindly feel free to contact me. You may also want to have a Look at Wikipedia which is a good starting point for such queries. Kind Regards, Tarun Gupta Panjab University Chandigarh-India Web: http://hotbacteria.tripod.com
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