Dihybrid CrossProblem 7: Homozygous offspring of a dihybrid cross.Tutorial to help answer the question In a dihybrid cross, AaBb x AaBb, what fraction of the offspring will be homozygous for both recessive traits?
Predicting the genotype of offspring

Since each parent has four different combinations of alleles in the gametes, there are sixteen possible combinations for this cross. Therefore we use a 4 square by 4 square Punnett Square. 
Now we can predict the outcome of the genetic cross of AaBb x AaBb. To determine the fraction of the offspring homozygous for both traits, first determine the genotype of an offspring homozygous for both traits. It would be aabb. 
There is only one of 16 possible combinations with this genotype. The predicted fraction is therefore 1/16. 
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