Why are there 9 different genotypes for this cross: AaBb x AaBb?

Question

Why are there 9 different genotypes for this cross: AaBb x AaBb?

Answer 1

The way to calculate this is to notice that for the A type of gene you have three possiblities AA, Aa, aa, for the B type of genotype you also have three types of genotypes BB,Bb, and bb.

multiply 3 * 3 = 9

Now how many genotypes would you have for  AaBbCcDd, it would be 3*3*3*3 = 81

Answer 2

aabb,AABB,AABb,AAbb,AaBB,AaBb,Aabb,aaBB,...

Answer 3

this is a dihybrid cross. if you do the punnett square, it looks something like this:

http://www.compumike.com/science/genetic...

count up the different genotypes; there are actually 16 different types.

mathematically, each allele has a probability of 1/2 of occurring, so take 1/2 to the 4th power to get 1/16. this means that there are 16 different genotypes.

you may be thinking of phenotypes: the ratio for a dihybrid cross is 9:3:3:1, so there are 9 different allele combinations to get the dominant phenotype for both alleles (9/16 chance).