Karyotype Displaying Extra 21st Chromosome |
So, how does one deal with this issue? The answer is X-inactivation, in which one copy of the X chromosome is condensed into a Barr body that becomes inactive because genes are not transcribed from it. This occurs in autosomal cells during early embryonic development. This process is known as lyonization, named after Mary Lyon, the British scientist who discovered it.
Picture of Mary Lyon |
To me, the most interesting part of this process is that it's completely random! It's impossible to know which chromosome will be deactivated, and in all female individuals, the same chromosome isn't deactivated everywhere. The only exception to this is in kangaroos where the paternal X chromosome is activated over the maternal X chromosome.
A Kangaroo |
A Calico Cat Displaying Mosaicism |
This cat had parents that were likely orange and black. On one X chromosome, there was a gene coding for black fur and on the other chromes there was a gene coding for orange fur. Since X inactivation is random, the cat has multiple patches of black and orange fur across her body. And if you were wondering, yes, female women are also mosaics! Although mosaicism doesn't come through as obviously in female humans, it shows up in more subtle ways like a lack of sweat glands in certain parts of a woman's body.
In conclusion, ladies don't let anyone tell you otherwise; you are literally a mosaic and a work of art.
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