8/27/14 – Independent Assortment and Punnett Squares

Following my research from yesterday and this morning, I have compiled some notes over independent assortment and Punnett squares. Here goes. 

Mendel’s Law of Independent Assortment says that each pair of alleles will separate independently (assuming the genes are not attached or linked to each other). 

Example: 

independent_assortmentSince the genes are not linked, each split allele can join with any of the other split alleles that aren’t its own, creating the possibilities of GY, GY, gy, gy, Gy, Gy, gY, and gY. 

A very easy way to illustrate this independent assortment and the possibilities that stem from it is with a figure known as Punnett Squares. Rather than explain the construction of a Punnett square, a visual is probably much easier to visualize and comprehend: 

punnett3

In the illustration, the Father’s Genes are listed at the top and the Mother’s genes on the left-hand side (since we read left-to-right here in the good ol US of A). The resulting middle squares show the results of a mating/pairing of these given gametes: Bb, bb, Bb, and bb. For the first square, the result is the father’s dominant gene (B) and a recessive (b) gene from the mother. The second result on the top row is from a recessive gene from the mother and a recessive from the father. The same results appear in the second row, since the mother has two recessive genes (the results would be different if the mother’s gene was Bb or BB rather than bb. 

Next, we will be talking about sex-linked genes, and next week, the role that probability plays (hint hint: a large one) in gene selection and heredity. Then, later next week – mutations!

 

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