If you start out with two pure breeing parents and cross them to get an F1 generation then self-cross the F1 generation with itself ( self-cross ) then cross the F2 with themselves ( self the F2 gen ) you will 3:1 ratio of the dominant phenotype in the F3 generation. Can anyone show me how to do the punnett square for the selfing of the F2 generation ? The thing I dont understand is how to do a punnett square when there are three different gamete combinations being crossed. This seems impossible to me. Thank you for your help.
You mean gametes with three different traits (trihybrid cross)? The Punnett square has 64 (4 x 16) entries, and is best done as a branch diagram (i.e. don't do all 64 combinations explicitly like in a Punnett square) but is not impossible. I'm sure there's an example in your Genetics book or online somewhere.
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