Humans
have 23 pairs of chromosomes, but only one pair determines our sex:
the X and Y chromosome. The Y-chromosome differentiates between male
and females; males have the Y-chromosome, females do not. However,
this may not have always been the case. The Y-chromosome is
substantially smaller than the X-chromosome, in terms of base pairs
and functional genes. The Y-chromosome has about two hundred
functional genes, while the X-chromosome has over a thousand genes.
A
recently study conducted by a team of scientist
composed of Henrik Kaessmann, Associate Professor at the CIG (UNIL)
and group leader at the SIB Swiss Institute of Bioinformatics, and
their collaborators in Australia released findings that the X and Y
chromosomes were once identical and around 180 million years ago the
Y chromosome began to lose non-essential genes and became unique to
eutherian males. They compared the three types of mammals; egg-laying
mammals such as the platypus, marsupials like the opossum, and
eutherians, which include humans. They sequenced DNA from
non-determining chromosome in both platypuses and opossums, and
sex-determining chromosomes in eutherian mammals and found the
Y-chromosome splits about 180 million years back. Through evolution,
elements common between the X and Y chromosomes, not related to sex,
became functionless and lost in the Y chromosome. This caused the
chromosome to shrink and made it the sole factor in determining sex
in eutherian mammals. The scientist predict that, at its current rate
of evolution, the Y-chromosome might eventual disappear completely.
However, this wouldn’t be the end of males..They predict another
split would have to occur in order to maintain sex determination.
The
Y sex-chromosome evolved from the X non-sex-determining chromosome.
The SRY gene, found on the Y chromosome, is one of the major genes
responsible for the development of testes. Its expression is present
in both platypuses and eutherians. This is one of the essential
elements that survived the split and was a useful gene in tracing the
split between chromosomes.
Posted by
Maxwell Liner (B)
I'm confused as to why the scientists predict the loss of the Y chromosome. As long as it remains sex determining why would it be lost and replaced with another splitting event?
ReplyDeletePosted by Tim Daly
This article is fascinating! I wonder why this reduction of the Y chromosome happened in eutherians and not other animals. Is their any explanation for this in the article you looked at?
ReplyDelete-JE
Other mammals have their sex determining genes are on a different chromosome. Other species have various ways of changing gene expression for sex determination, i.e alligator/croc sex is determined by the temperature the eggs incubate at. The reduction of the Y-chromosome in us was bc it was full duplicated or non functional coding..the big player in the game..The 12 or so sex determining genes..are what really matter.
DeleteMax Liner
I agree with Tim. What would the male chromosome look like of the Y chromosome had disappeared?
ReplyDelete-Chelcie C.
Wow this is a very interesting post. Has there been many researchers that agree and are studying this as well?
ReplyDeletePosted by Kristen Whitehead
Love the comments..and I have been having the same thoughts.This was a pretty recent discovery when I first wrote this and during the last week there have been a flurry of other papers, all with different opinions on the matter.. but I think these researchers were suggesting, over thousands and thousands of generations, through recombination and other mutations, that the 12 genes necessary for sex determination in mammals might appear somewhere other than the Y-chromosome, and the Y-chromosome could potentially disappear if the chromosome itself is no longer needed..simply based on its current rate of evolution..however its just a thought and an extremely simplified version of the evolution going on.
ReplyDeleteMax Liner