Wednesday, October 6, 2010

Probability by Punnett

Sir Reginald Punnett was born at the turn of the 20th century in England.  While in medical school at Cambridge University he became interested in research and starting working on reproducing Mendel's experiments with Bateson a professor at the college.

He noted the need for a mathematical tool to predict phenotype and turned to his mathematician cricket partner to help devise a tool.  Thus the Punnett square was born!

http://post.queensu.ca/~forsdyke/bateson3.htm
The picture above shows Reginald Punnett (left) with his professor and then colleague William Bateson.  As their experiments progressed, they soon realized the vast body of research that lay before them and the rest of the scientific community.  The started the first genetics department at Cambridge University.


Oh Punnett squares!  How we love thee!

Punnett squares allow scientists to predict how traits will be passed along in generations of the same species.

http://cockatiels4u.tripod.com/algenetics4.htm
As you can see above, in a monohybrid cross (only focusing on 1 trait) you place the possible alleles (form of gene; like for height: tall and short) on each side being sure to keep the alleles for each parent on separate sides.

Then you simulate all the possible combinations of gametes by writing the allele donated from each parent in the box.  Use the arrows above to review how to place each allele in the appropriate box.

The resulting genotypes are the probable genetic combinations for the offspring of the parents.  Punnett squares more so prove what is not possible.

In the square above, all genotypes are possible because each parent has a copy of both dominant and recessive alleles making all combinations doable.

In addition to using your flashcards we made today, visit the link below to experiment with the Punnett square calculator.  It not only shows a square for monohybrid crosses, but also allows you to view dihybrid and trihybrid crosses!

Punnett Square Calculator


As we learn more types of inheritance, you will find that while phenotype possibilities expand, Punnett square set up really only comes down to the 6 scenarios you translated into flashcards.

Get to practicing your Punnett squares my lovelies!

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