- Mar 20, 2013
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While knowing what the grandparents were is helpful if you don't "see" something in your pair but think one or both might be split for something, you really don't need the previous generation information. Once you know what the parents are, that's all you need to figure out what the offspring will be. Remember, it doesn't matter if Grandma was Pied. What matters is if Daddy got the Pied or White gene -- it's one or the other. Grandma can't give Daddy both. If Daddy didn't get the White gene from Grandma, and he certainly didn't get it from straight IB Grandpa, then Daddy doesn't have the White gene -- he has one copy Pied (from Grandma) and one copy Normal (from Grandpa). It doesn't matter what an ancestor carried if it didn't get passed on to the next generation in the line.
As an example, let's say Grandma was Single Factor White Eye. If Daddy doesn't show the White Eye trait in Single Factor form (i.e. some but not all ocelli are white), then Daddy doesn't have the gene for it -- and thus Daddy can't pass it on to offspring. So it's sort of extraneous information. It's helpful to keep in mind if both grandparents are split to the same "invisible" recessive mutation (say, Bronze, for example) and Daddy looks like regular India Blue. He MIGHT be split to Bronze, but you couldn't tell by looking at him. If you paired him to a Bronze hen and got some Bronze offspring, then you could look back and say "Ah, even though he looks IB, he had split-to-Bronze parents, so he must have gotten one copy from one of them." So it clarifies what he is -- test breeding. But like I said, once you know "what he is", you don't need to put grandparents' information in a Punnett Square. It's really something better saved for a pedigree, to keep in mind if you want to avoid inbreeding ("oops....these two are actually cousins...and I don't want that").
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