19-03-2018, 02:38 PM
http://www.isna.org/faq/y_chromosome
Want to know more? The following comes from ISNA’s Medical Advisory Board member Dr. Charmian Quigley:
SRY, discovered in 1989, is a small gene located at the tip of the short arm of the Y chromosome. So what does it do? Actually, like all genes, it does nothing except to act as a blueprint for a protein. In this case, the protein of the same name does funky things to DNA, like bending it and unwinding the 2 strands, so that other proteins can get in and attach themselves to other genes that are then turned on. So how did this gene get its reputation (and its name) as the “sex determining” gene?
As is pretty common in the world of genetics, this was because of some errant mice. Researchers in England took a laboratory-made copy of this gene and inserted it artificially into a female (XX) mouse embryo at a very early stage of development. The mouse was “converted” from female to male, so the gene must have been responsible – right? Well, maybe not. A few years later, a similar gene was found on human chromosome 17. When the important part of this gene was inserted into a female mouse embryo, the same thing happened. Voila! A male.
So now we have 2 genes that can turn a female into a male, and one of them is not located on the Y chromosome! How can that be? It turns out that SRY is probably just a facilitator that allows a more critical gene (or genes) to function, by blocking the action of another opposing factor. Can the magic of genetics do the opposite – turn a male into a female? Indeed it can. A gene on the X chromosome (the chromosome one typically associates with “femaleness”) called DAX1 when present in double copy in a male (XY) mouse, turns it into a female.
So now we have genes on the Y that can turn females with XX chromosomes into males and genes on the X that can turn males with XY chromosomes into females… wow! Maleness and femaleness are NOT determined by having an X or a Y, since switching a couple of genes around can turn things upside down.
In fact, there’s a whole lot more to maleness and femaleness than X or Y chromosomes. About 1 in 20,000 men has no Y chromosome, instead having 2 Xs. This means that in the United States there are about 7,500 men without a Y chromosome. The equivalent situation - females who have XY instead of XX chromosomes - can occur for a variety of reasons and overall is similar in frequency.
perhaps we are all XX from the beginning!
Want to know more? The following comes from ISNA’s Medical Advisory Board member Dr. Charmian Quigley:
SRY, discovered in 1989, is a small gene located at the tip of the short arm of the Y chromosome. So what does it do? Actually, like all genes, it does nothing except to act as a blueprint for a protein. In this case, the protein of the same name does funky things to DNA, like bending it and unwinding the 2 strands, so that other proteins can get in and attach themselves to other genes that are then turned on. So how did this gene get its reputation (and its name) as the “sex determining” gene?
As is pretty common in the world of genetics, this was because of some errant mice. Researchers in England took a laboratory-made copy of this gene and inserted it artificially into a female (XX) mouse embryo at a very early stage of development. The mouse was “converted” from female to male, so the gene must have been responsible – right? Well, maybe not. A few years later, a similar gene was found on human chromosome 17. When the important part of this gene was inserted into a female mouse embryo, the same thing happened. Voila! A male.
So now we have 2 genes that can turn a female into a male, and one of them is not located on the Y chromosome! How can that be? It turns out that SRY is probably just a facilitator that allows a more critical gene (or genes) to function, by blocking the action of another opposing factor. Can the magic of genetics do the opposite – turn a male into a female? Indeed it can. A gene on the X chromosome (the chromosome one typically associates with “femaleness”) called DAX1 when present in double copy in a male (XY) mouse, turns it into a female.
So now we have genes on the Y that can turn females with XX chromosomes into males and genes on the X that can turn males with XY chromosomes into females… wow! Maleness and femaleness are NOT determined by having an X or a Y, since switching a couple of genes around can turn things upside down.
In fact, there’s a whole lot more to maleness and femaleness than X or Y chromosomes. About 1 in 20,000 men has no Y chromosome, instead having 2 Xs. This means that in the United States there are about 7,500 men without a Y chromosome. The equivalent situation - females who have XY instead of XX chromosomes - can occur for a variety of reasons and overall is similar in frequency.
perhaps we are all XX from the beginning!