Expert: Dana Krempels, Ph.D. - 1/18/2012

Question
I finished a bio quiz today, where we were asked to do very large Punnett square problems, even though we've only done simple ones in class. We've learned about the 9:3:3:1 ratio for heterogeneous dihybrid crosses, but that's the most complicated thing we've done.
The questions were something like:
what are all the genotypes for something with a genotype AaBBCCDDEE and their frequencies? ..I would have to draw 625 squares if i actually did the Punnett square, right? How do I solve this type of problem with pencil, paper, and a calculator?
Another was
if you have cross FFGgHh and FfGgHh, what frequency will you get AaBbCc offspring?

What kind of calculations or math or whatever can I use to solve these bigger Punnett square problems??

Answer
Dear Sara,

Well, that was sort of a trick question.  If the genotype was really AaBBCCDDEE, then there are only TWO possible gamete types with respect to those genes, because only one of those loci is heterozygous.  So your two gamete types would be:

ABCDE and aBCDE

(d'OH!)

I'm not sure the second question is written correctly, since the gene abbreviations are different for parents and offspring.  Is that a typo?

Hope that helps.

Dana