Wednesday, April 4, 2018

X-inactivation

When looking at calico cats its pretty much assumed that it is female. This is do to the fact of X-inactivation taking place in mammals chromosomes. As most people know, males have an X and a Y chromosome whereas females have two X chromosomes. However, one of these two chromosomes found in female cells gets inactivated which is the main mechanism behind calico cat color.



This inactivation is done by condensing the randomly chosen X chromosome into whats called a Barr body. Xist is the gene that encodes a non-coding RNA which then recruits proteins back to that X chromosome. These proteins super condense the chromosome into a Barr body which inhibits transcription to take place therefore becoming inactive in the cell.

This means that, if a cat is heterozygous for the black and orange allele, then one of the X chromosomes contains the orange allele and one contains the black allele. When the cell randomly decides which X chromosome to deactivate it can be either the orange or black allele. Each cell makes its own decision that will be later inherited by its progeny therefore there is the possibility of both orange and black to appear in the phenotype.

Its pretty interesting to think about X-inactivation random choices to have such an impact on an organism in terms of its phenotypic appearance. Thanks to this mechanism occurring in mammal cells, we have this beautiful cat type!

Posted by Sarah Aboody (1)

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8 comments:

  1. Peter HoulihanApril 5, 2018 at 3:32 PM

    Calico cats having multicolored fur is similar to humans who have mosaic skin pigmentation. It works very much the same as you mentioned and results in uneven and different colored skin tones.

    -Trung Le (2)

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    1. Peter HoulihanApril 9, 2018 at 10:26 AM

      Thats so interesting, I never thought of it in that way as to humans. It is cool to think of the ways that X inactivations can lead to different phenotypes.

      -Sarah Aboody (1)

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  2. Peter HoulihanApril 6, 2018 at 9:48 AM

    If one of the chromosomes code for orange ,and one for black, and one is deactivated at the time where does the third (white) color come in?

    Zane Ruehrwein (3)

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    Replies
    1. Peter HoulihanApril 9, 2018 at 10:28 AM

      Thats a whole different mechanism that I am unaware of. I think it has to do with something when both of those genotypes are expressed at the same time. Thats a good question!

      -Sarah Aboody (1)

      Delete
    2. UnknownMarch 29, 2019 at 12:13 PM

      The white patches are caused by a different gene. A gene that controls pigmentation.

      Delete
  3. James Bowler (3)April 6, 2018 at 5:55 PM

    This is a very fascinating case of genetic mutation ! I wonder what other affects the x-inactivation has besides color.

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  4. Peter HoulihanApril 6, 2018 at 8:41 PM

    This is so interesting! Do you think X inactivation affects more than just the color? There are other genes on the X chromosome, what other effects if any are present with this phenomenon?

    Posted by Sarah Kamukala

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