Tuesday, October 11, 2011

Brain Droppings - vol 12

It's Tuesday! The day of brain droppings....
*I need to redo this picture... The brain is supposed to be hopping 
AWAY from the jar but we all read left to right so.....

Basic genetics 101:
Mammals have X and Y sex chromosomes... 
If you're a guy, you have X (from mom) and Y (from dad).
If you're a girl, you have X (from mom) and X (from dad).

Sex chromosomes have thousands of genes with much wider effects than just sex differences.  For example, the X chromosome determines coat color in kitties.

Normally, in the womb, the little developing female kitty decides which of the two Xs to keep (mom's or dads).... cuz you only need one... and it suppresses the other. Sometimes, this suppression fails and the genes from both Xs are expressed.

Enter calico cats!

Their coat is a physical representation of this effect (1/2 coat color from mom, 1/2 from dad).
Because this only occurs with two X chromosomes, calico cats are almost* always female!

Cool, huh?

*The exception is the rare XXY male.
Your turn! Got a cool fact to share with me? 


  1. All my facts make me seem extra slow when I'm trying to match wits with a neuroscientist!!!

    But I do love calico kitty cats... and as usual I feel a little bit smarter having read your blog.

    *** and my word verification was "le dumb" ~ I'm not even kidding... ***

    le dumb

  2. No interesting fact to share, but I can't believe the number of people that don't remember learning about chromosomes in school. So many people don't believe me when I say its the dad that determines the sex of baby, not the mom.

  3. Yeesh. I love Brain Droppings. I always learn something. (Also the title makes me giggle)


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