Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: cheryl j on 21/02/2012 20:41:15
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I was listening to a physiology lecture on the reproductive system, and the lecturer stated that the Y chromosome contains almost no genetic information, just the "switich" to turn on maleness, which I assumed means the production of hormones that changes which genes are expressed during fetal development and puberty.
In anthropology, though, they are always talking about different enviromental, evolutionary pressures on males and females, resulting in differences beyond having bigger muscles, denser bones, or aggression, sthings like brain structure and function. But if there is nothing on the Y chromosome, how are these differences passed selectively to males? Is it all "hidden" on the non-sex chromosomes, and only expressed with large amounts of testosterone?
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According to Wikipedia:
In humans, the Y chromosome spans about 58 million base pairs (the building blocks of DNA) and represents approximately 2% of the total DNA in a male cell. The human Y chromosome contains 86[26] genes, which code for only 23 distinct proteins. Traits that are inherited via the Y chromosome are called holandric traits.
The human Y chromosome is unable to recombine with the X chromosome, except for small pieces of pseudoautosomal regions at the telomeres (which comprise about 5% of the chromosome's length). These regions are relics of ancient homology between the X and Y chromosomes. The bulk of the Y chromosome which does not recombine is called the "NRY" or non-recombining region of the Y chromosome. It is the SNPs in this region which are used for tracing direct paternal ancestral lines.
One of the genes encoded is the SRY Gene.
SRY (Sex-determining region Y) is a sex-determining gene on the Y chromosome in the therians (placental mammals and marsupials).
This intronless gene encodes a transcription factor that is a member of the SOX (SRY-like box) gene family of DNA-binding proteins. This protein is the therian testis determining factor (TDF), referred to as the sex-determining region Y protein or SRY protein which initiates male sex determination. Mutations in this gene give rise to XY females with gonadal dysgenesis (Swyer syndrome); translocation of part of the Y chromosome containing this gene to the X chromosome causes XX male syndrome.
Anyway, it appears as if much of the "maleness" is controlled by the SRY gene. And, if expressed in XX females (http://en.wikipedia.org/wiki/XX_male_syndrome), it will turn on maleness characteristics, and if it fails to express in XY males (http://en.wikipedia.org/wiki/XY_gonadal_dysgenesis), then they will not get male characteristics, and thus would default to females.
Both males and females can produce testosterone, but more in the males, so I believe the regulation of testosterone production in the gonads by SRY is critical to the development of males.