Reptile & Amphibian Forums

I have been laerning about the Punnet square. Ive got the basics down but having some trouble doing double hets. If some one knows how to calculate these please help me out.

Thanks

Andy

Here is a link
Genetic Wizard

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www.BallPython.Us
DISCUSSION BOARD

They use the branching system (AKA forkline, etc) instead.

A pair of double hets - Aa Bb x Aa Bb.

Do a Punnett Square for the "a" locus and then the "b" locus. Result:

a locus | b locus
----------------
1/4 AA | 1/4 BB
2/4 Aa | 2/4 Bb
1/4 aa | 1/4 bb

To get all possible results, combine each "a" locus genotype with every "b" locus genotype and multiply the fractions as follows:

1) Combine the first "a" locus genotype with the first "b" locus genotype and multiply the fractions.

2) Combine the first "a" locus genotype with the second "b" locus genotype and multiply the fractions.

3) Combine the first "a" locus genotype with the third "b" locus genotype and multiply the fractions.

4) Combine the second "a" locus genotype with the first "b" locus genotype and multiply the fractions.

5) Combine the second "a" locus genotype with the second "b" locus genotype and multiply the fractions.

6) Combine the second "a" locus genotype with the third "b" locus genotype and multiply the fractions.

7) Combine the third "a" locus genotype with the first "b" locus genotype and multiply the fractions.

8) Combine the third "a" locus genotype with the second "b" locus genotype and multiply the fractions.

9) Combine the third "a" locus genotype with the third "b" locus genotype and multiply the fractions.

1) 1/16 AA BB
2) 2/16 AA Bb
3) 1/16 AA bb
4) 2/16 Aa BB
5) 4/16 Aa Bb
6) 2/16 Aa bb
7) 1/16 aa BB
8) 2/16 aa Bb
9) 1/16 aa bb

Total the fractions, and you will see that there are 16/16, which means all possible combinations are in the list.

If you think of the "a" locus list of genotypes and the "b" locus list of genotypes as a pair of three-place rotors, you will see that the "b" rotor makes a full revolution before the "a" rotor moves one place. For every additional locus, add another rotor.

Here's a mating problem. Aa Bb cc DD Ee x Aa Bb CC Dd ee
1) What fraction of the babies will be aa BB Cc DD ee?
2) What fraction of the babies will be Aa BB cc Dd Ee?

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Answers:
1) 1/4 aa - 1/4 BB - 1/1 Cc - 1/2 DD - 1/2 ee = 1/64 aa BB Cc DD ee
2) None of the babies will be Aa BB cc Dd Ee because cc is impossible to produce from this mating.

Paul Hollander