Sunday, October 6, 2013

Punnett Squares: 2013 version

Genetic Genealogy is again in the news because 23andMe has acquired a patent for their Family Inheritance Traits Calculator.  Some are criticizing this technology as enabling prospective parents to create designer babies and that this is wrong.

At 23andMe, both my parents have tested, so I can show you what Family Inheritance Traits Calculator looks like for two actual parents and their offspring.

Family Inheritance Traits Calculator
All of the offspring will be able to taste bitter and will not be lactose intolerant.

My genotype for eye color is GG.  I received my father's recessive gene.
My mother only had recessive genes to give.
My result is blue eye color, but green and brown are possibilities in siblings.  (We all have blue eyes.)

You have two genetic instructions (genotype) for traits (except for the Y chromosome, which is not really relevant for our discussion here).  One gene is from your mother and one is from your father.  The trait that is shown in the offspring (phenotype) depends on how the genes interact with each other:  they can be dominant, co-dominant, or recessive.  (Or are expressed based on other factors that we need not bother with here.)

In biology class, you drew Punnett Squares to demonstrate the likelihood of possible traits for offspring of two parents.  Think:  Mendel's flowers.

Punnett Square.
Yellow is dominant over green and will be the expressed trait in offspring who inherited that gene.

Breeders of animals and plants carefully select parentage to produce desired traits in subsequent generations.

And humans have been practicing mate selection since the beginning of time, consciously and subconsciously, favoring those with traits that promote survival and provide desired physical appearance.   People carefully select sperm donors and egg donors based on inheritable traits.  23andMe's Traits feature is really just a modern-day Punnett Square.  Labs can analyze DNA to reveal genotypes and then computers calculate traits in theoretical offspring.  The practice is not new- the technology is.

Punnett Squares is now computerized.