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The major gene of the Y-chromosome is SRY. Would it be possible to get the X-chromosome and add SRY to create a "fuller" Y-chromosome?

What advantage does the skinny Y-chromosome give an individual anyway? Females only use one X-chromosome (via the Barr body) so they don't seem to gain as much from having the pair.

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    $\begingroup$ Females do not always use only one X chromosome - eg Drosophila. And why would an X with SRY be better than the current Y? It is not junk - it is now being found to affect many genes through epigenetics. $\endgroup$ – rg255 Dec 31 '12 at 10:54
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SRY translocation to the X chromosome clinically exists and characterizes the De La Chapelle Syndrome. The phenotype associated to this syndrome demonstrates the necessity of other components on the Y chromosome to develop full masculine characteristics.

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Would it be possible to get the X-chromosome and add SRY to create a "fuller" Y-chromosome?

Possible? Sure. You could sequence both chromosomes and then create some artificial DNA that included the combined sequences.

Would it be viable? Probably not.

What advantage does the skinny Y-chromosome give an individual anyway?

If there is a genetic condition in the father's X-chromosome, the male child is spared from it.
If there is a genetic condition in the mother's X-chromosome, the male child has a 50/50 shot at being spared from it.
If the genetic condition requires two homogenous X-chromosomes, the male child is spared.
If the genetic condition requires two heterozygous X-chromosomes, the male child is spared.

These are all advantages of simply requiring a Y-Chromosome, and there are certainly disadvantages to having a Y-Chromosome as well; X-linked genetic disorders will definitely affect any male heirs, unlike...

Females only use one X-chromosome (via the Barr body) so they don't seem to gain as much from having the pair.

...Female offspring. Because women have two X-chromosomes they have redundancy. If there is a bad gene on the extra X-chromosome that is deactivated, then it doesn't matter - where for a man with the same X-chromosome it would definitely affect them.

Also, because of the redundancy, what X-linked conditions do exist usually affect women less-so. If both X-chromosomes are utilized for a specific gene, then one bad protein product is partially made-up for with the one good protein product.

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  • $\begingroup$ If the genetic condition requires two homogenous X-chromosomes, the male child is spared..... hmmm can you point to an example of that? If the condition is recessive the male child is definitely not spared. $\endgroup$ – nico Dec 29 '12 at 8:53
  • $\begingroup$ Nope, as I'm not sure if one exists. I was being hypothetical. $\endgroup$ – MCM Dec 29 '12 at 13:15
  • $\begingroup$ Further points> Y chromosomes, contrary to popular belief, are not junk - they contain very few genes but these can have epigenetic effects (for example via regulation of other genes). This gives a huge benefit to even "skinny" Y chromosomes because it offers the opportunity to resolve intralocus sexual conflict as it is male limited. Another point is that females do not always use just one of the X chromosomes (X inactivation). Some species use other methods of dosage compensation - drosophila males double the transcription of their X to match the output of both in the females. $\endgroup$ – rg255 Dec 30 '12 at 14:28
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Would it be possible to get the X-chromosome and add SRY to create a "fuller" Y-chromosome?

Yes. Nature has done that. https://en.wikipedia.org/wiki/XX_male_syndrome However there are more there is more than just the SRY gene on the Y chromosomes. As such XX males with SRY translocations are sterile.

What advantage does the skinny Y-chromosome give an individual anyway?

To an individual nothing much (as far as we know). However Y bearing sperms swim faster as they have smaller heads than X bearing sperm. So much so that for every 100 girls conceived, there are 140-160 boys conceived.

Females only use one X-chromosome (via the Barr body) so they don't seem to gain as much from having the pair.

Actually there is a lot to gain. X inactivation is random. So female tissue is composed of a mosaic of cells expressing one or the other X chromosome. So if there is deficiency in one allele, the other allele can compensate at the tissue level. This is why despite so many boys being conceived, only 106 boys for every 100 girls are born.

Also why women have smaller standard deviation in intelligence than men (as many of the genes regulating intelligence are on the X)...So while there are fewer women with super high IQ, there are also fewer women with super low IQ.

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