Sarah Albee: Allele Help From My Friend

From: Sarah Albee
July 23, 2012 at 05:55AM

On Friday, I blogged about the Hapsburg chin and the seriously shallow gene pool shared by so many European monarchs of the seventeenth century. I have a friend, Laura, who is a scientist with expertise in genetics. She teaches AP biology, a notoriously difficult and time-consuming course, at an elite and highly challenging private school. And she also teaches a post AP bio class, which is a research-based biology class for kids who couldn’t get enough of her AP bio–and kids flock to it.

Anyway Laura read my blog on Friday, and she emailed me this Hapsburg family tree with the comment, “Wow. A pedigree should not look like this.”

I asked her to explain what was going on in biological terms. Here’s what she said:

  • So the basic idea behind the negative effects of inbreeding is that it increases the likelihood of getting two copies of a bad allele.
  • Quick background: we have two copies of every gene – one we inherit from mom, one from dad.  Different versions of a gene are called alleles.  In order to see the effect of some alleles, we need TWO copies.  For other alleles, we need only one (the classic example is brown eyes and blue eyes.  We need only one brown eye allele to have brown eyes, but we need two blue eye alleles to have blue eyes.)
  • We tend to look like relatives because we share alleles with them- thus, if two relatives mate, there is an increased likelihood that their child will inherit the same allele from both mom and dad, since it is more likely that mom and dad both have that same allele in the first place.  Oftentimes, alleles that have negative effects are “recessive”- like the blue eye allele, two copies are needed to see an effect.  Thus, inbred individuals, who have an increased chance of having the same two alleles for any gene, are more likely to express these bad alleles.
  • As you might guess, inbreeding is pretty complex and not all organisms show negatve effects from it.

Aren’t teachers awesome?



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