Thursday, April 7, 2016

Punnett Squares

Hello and welcome back to my blog! Without further ado, here is today's topic: Punnett squares. I am learning about these in Introduction to Genetics and Evolution through my online Coursera course taught by Dr. Mohammed Noor at Duke.


Punnett squares, named after Reginald Crundall Punnett, are ways to calculate rate of inheritance, X-linked inheritance, and genotype frequencies. When used in their most basic state, the squares are used for determining basic genotypes for a single gene. For example, if you were to cross an "AA" individual with an "aa" individual, the genotypes of all of the offspring would be "Aa", as demonstrated below:

Another, more extended use of Punnett squares is X-linked inheritance. X-linked inheritance is gender-specific, so they differ based on males or females. Females, who have 2 "X" alleles where males have 1 "X" allele and 1 "Y" allele, which determines gender. For example, say you are studying red-green color-blindness, which is theoretically an X-linked disease. If a color-blind male (diseased "X" + "Y") mates with a carrier female (diseased "X" + "X"), the offspring has a 25% chance of being a color-blind female(diseased "X" + diseased "X"), a 25% chance of being a color-blind male (diseased "X" + "Y"), a 25% chance of being a carrier female (diseased "X" + "X"), and a 25% chance of being a healthy male ("X" + "Y"), as shown below:

The final and most complex use of a Punnett square is to calculate genotype frequencies. While what I am describing here may sound a bit far-fetched, it does actually occur in some invertebrate aquatic creatures. For example, if you know that the alleles are 70% "A" and 30% "a" in a certain allele "pool", then you can figure out that 49% of the individuals spawned from that "pool" will be genotype "AA", 42% will be "Aa", and the remaining 9% will be "aa", as demonstrated below:

Thank you for visiting School Stories (Where School Is ALWAYS In Session!) today, and I hope to see you again soon!

1 comment:

Zach said...

This is great! I remember doing these in school, too. They're fun to map out and see where your personal genetic traits came from and what you might have as a carrier. Good work!