Chromosome Y — Part 2

Welcome back to our fascinating two-part post showcasing the best of genetics in 250 words.  Today we dish about chromosome “Y.” Smaller than his sex-partner “X, “the still mighty “Y” has been shedding genes over the eons and becoming more stable.    Just recently some very savvy genetic researchers were able to determine that the “Y” has been stable for millions of years!  Which is a big deal because there was a time when it was believed that “Y” was very slowly shrinking right out of existence ~ rendering men themselves obsolete. Thankfully that is not the case.

Some interesting facts about the “Y:”

  • Its sex-determining superpower was discovered by geneticist Nettie Stevens in 1905 at Bryn Mawr College.
  • Only the tips, or telomeres, of the “Y” and “X” chromosomes recombine.  The rest of the “Y” chromosome is passed on to the next generation intact. This makes the rule-breaking “Y” handy for investigating recent human evolution from a male perspective. (not that we don’t appreciate all that “X” does for us.)
  • “Y” actually has a lot to do not just for the embryo, but all through adulthood in every tissue, not just male reproductive tissue.  This finding was just published last week in the journal Nature.
  • Only mammals have the “Y” (and “X”, too).  Some reptiles have no sex chromosomes at all.  The sex of their offspring depends on the incubation temperature of their eggs.   Others are hermaphroditic (meaning they contain both male and female gametes in the same individual).

This is really just skimming the surface of “X” and “Y.”  But it’s thrilling how we are still finding out about what makes us human.  And how much diversity there is within us — even as we’re still quite similar looking as a species.




Chromosome X — Part 1

We are in the final laps of the A-to-Z Challenge, which means today’s post is about the “X” chromosome.  First, a little genetic refresher about the sex determining 23rd pair of chromosomes:   females have two “X”  chromosomes and males have an “X” and a “Y”….. but more about the “Y” tomorrow.

Here are some facts about the “X”:

  • The “X” holds about 2,000 genes.  (vs. the “Y’s” 78 genes.  Again, stay tuned tomorrow)
  • The “X” is somewhat mysterious.  Females deactivate one of their “X” pairs, but scientists are not sure why.
  • The “X” holds an enormous amount of genetic diversity (and you know what Darwin had to say about that) because each copy of the X chromosome contains versions of genes not found on its partner.
  • Even though the “Y” is what determines male from female, there is stuff on the “X” that’s needed to support cellular activities required to actually make a boy, like androgen receptor.  Here’s a link to an expert, Jessica Profato of Stanford University, giving a far more elegant lesson in simple language — Understanding Genetics.   In all fairness she’s answering an elementary school student’s question, but I have no recollection of discussing this in my 5th grade science class.

Genetics is fascinating.  It’s what gives us the physical specimens of supermodels and super athletes.  It’s random and magical that humans are still making people with this one sperm and one egg technology —  it is the original DIY project.*

* OK — technically you have to work with a lab partner.