Attached earlobes are inherited as an autosomal recessive. An individual who cannot curl his tongue is homozygous recessive at another autosomal gene locus. A dihybrid female mates with a man who has attatched earlobes and cannot curl is tongue. What phenotypes are possible for thier children and in what ratios?
Once the parent's genotypes are known, the gametes each can produce will be known as well. Let E represent free earlobes which is dominant, and e represent attached earlobes, which is recessive. Let T represent tongue rolling which is dominant and t represents non-tongue rolling, a recessive trait. Therefore, the mother's genotype is dihybrid and can be represented by EeTt. The father has both recessive traits and is homozygous for each. His genotype is eett. The mother can make four different gametes--ET, Et, eT and et. The father can make four gametes but they are all the same--et, et, et, et. In a punnett square with four boxes across and four down, you can figure out all the combinations of offspring using the four gametes each parent produces. The results of the offspring are 4 hybrid free earlobes, hybrid tongue rollers (EeTt). There will be 4 hybrid free earlobes and homozygous non-tongue rollers (Eett). There will be 4 homozygous attached earlobes and hybrid tongue rollers(eeTt). And finally, there will be 4 homozygous free earlobes and homozygous non-tongue rollers(eett).