So Hey, for the problem 3's on the practice test, it has two major parts. The first is figuring out how many genes you have and which mutants are in which genes. This relies upon complementation. The second part is to figure out what the dominance/recessive relationships are for the different alleles within a gene. Complementation Basic Rules 1) All mutants must be recessive and true breeding for this to work. a) The line where all mutants are crossed to wildtype tells you if the mutants are recessive or dominant to wildtype. b) The diagonal where the mutants are crossed to themselves tells you if they are true breeding.
2) A complementation test is when you cross two mutants together and test the phenotype in the F1. There are two possibilities. a) If the mutants are in the same gene then the F1 phenotype will be a mutant phenotype and not wildtype. b) If the mutants are in different genes, then the F1 phenotype will be wildtype. The best way to do this problem is start with mutant 1 x mutant 2 and ask are they in the same or different genes. Then move on to mutant 1 x mutant 3 and the ask same question. This will give you a list of mutants in the same gene as mutant 1 and a list of mutants that are not in the same gene as mutant 1. Then proceed through the list of mutants that are not in the same gene as mutant 1 just as you proceeded through the original list. Try working through the problem in this stepwise manner and see how it goes. The next step is to test the dominance versus recessive. Line 1 tells you how the dominance/recessive goes with relation to wildtype. The same analysis can be done between two mutants that are within the same gene. So for example let's say WT is AA and causes purple, mutant 10 is a10a10 and causes light purple and mutant 22 is a22a22 and causes white. If you cross both mutants to wt, they F1 are purple, thus both mutants are recessive to wt. The next step is to cross the mutants to each other to create the a10a22 heterozygote. Let's say the phenotype of the a10a22 heterozygote is light purple. That would mean that the a10 allele is dominant to the a22 allele. This could be written as A>a10>a22. I hope that this helps. Dan