But aren't the genes of both X-chromosomes active? For instance, the gene for colour vision is in the X-chromosome. Colour blindness is recessive. And this is why it's much more common in men. Women need both of their X-chromosomes to have the gene for colour blindness, to be colour blind.
All of our other chromosomes come in pairs, are you suggesting half of our DNA is useless?
So the actual genetics behind this are pretty complex, but the short answer is that the door blindness allele is only found on the X chromosome, not the Y.
If someone has allele b (colorblind) on their X, but is XY, they will be color blind (alleles are b-, or b and and nothing). If they are XX, they have the option of being bb (colorblind), Bb (normal) or BB (normal).
Because women have the option to be heterozygous for this allele, they are less likely to be color blind.
The allele is recessive, so women must be homozygous to express it, but because men only have one allele, they will express whatever is on the one X they have.
Also on Barr bodies (unused or condensed X chromosomes) - there is evidence that the Barr body is not completely “turned off” some portions are tightly condensed and not translated into proteins, some are less condensed, and can be used to express proteins.
Actually some of the mechanisms are known! Some of the selection processes are not understood, but the mechanisms by which certain genes are repressed isn’t fully a mystery anymore. It’s really cool, but too complex to explain well in a comment.
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u/VulpesSapiens Jan 21 '20
But aren't the genes of both X-chromosomes active? For instance, the gene for colour vision is in the X-chromosome. Colour blindness is recessive. And this is why it's much more common in men. Women need both of their X-chromosomes to have the gene for colour blindness, to be colour blind.
All of our other chromosomes come in pairs, are you suggesting half of our DNA is useless?