Question

Analyze the results of a cross between two organisms that are both heterozygous for two different genes (AaBb). Use a Punnett square to evaluate the possible genotypes. (1) List all the genotypes from your Punnett Square in the answer space. (2) Determine how many phenotypes can be produced in the offspring. (3) Determine the probability of producing offspring with the aabb genotype.

Answer 1

1) all the possible genotypes are also identified by color in the image below :AABBAAbB or AABbaABB or AaBBaAbB or aABb or AabB or AaBbAAbb 
aAbb or AabbaaBB
aabB or aaBbaabbThere are 9 different genotypes in total. These can be achived by mixing the alleles of both genes of each parent (just like it's represented in the square).

2) there are 4 phenotypes
-one with an allele A and allele B that would dominate the other. (AABB, aAbB, for example)
- one with all alleles recessive-  aabb
-one with the recessive alleles in the gene A but heterozygotic/homozigotic dominant for gene B ( for example: aaBB)
-one with the recessive alleles in the gene B but heterozygotic/homozigotic dominant for gene A ( for example: Aabb)

3) probability of having offspring with the aabb genotype: 1/16
Just by looking at the punnet square, you can see that only one has the aabb genotype, in all the 16 possibilities.