Question

. . . Activity E. Predicting the outcome of a dihybrid cross The resulting phenotypic ratios in the F2 generation of a dihybrid cross (2 traits) can be quite different than those observed from a monohybrid cross. But the process is essentially the same. First you list all possible gametes each parent and subsequent parents can produce. Second, you then assign the gamete possibilities to the Punnett square and fill it in. Finally you count the progeny and determine the number of progeny in each phenotypic category. Remember, when determining the types of gametes possible, each gamete must have one member of each homologous pair of chromosomes. For example, if you are considering a T gene (ability to taste PTC) and an F gene (unattached earlobe), each gamete must have one allele for the T gene (either T or t) and one allele for the Fgene (either Forf). 1. What type of gametes will the following genotypes produce? Genotype: TTFF Gametes TF Genotype: TTFF Gametes TF EF Genotype: ttff Gametest Genotype: TtFf Gametės TE TfitF, tf TTFF tiff Cross or mate a homozygous tasting and unattached earlobe parent with a homozygous non tasting attached earlobe parent? 2. What are the genotypes of these two parents? TF TT FFF tf - TF, tf 3. What type of gametes can each parent produce? TF and tf 4. How many different types of gametes can each parent produce/Record the genotypes of the gametes each parent can produce. tt ff 5. Construct the Punnet square that shows the cross between the parents. This can be Revised Spring 2017 Biology& 160 Laboratory Manual

Answer 1

1) a) TTFF: can produce only one type of gamete, that is TF only.

b) TtFF: can produce TF or tF gametes.

c) ttFf: can produce tF or tf gametes.

d) TtFf: can produce TF, Tf, tF and tf gametes

2) genotype of the parent who is homozygous for the unattached earlobe and PTC tasting is TTFF and genotype of the parent who cannot taste PTC and having attached earlobes is ttff.

3) TTFF parent produces TF gamete and ttff parent produce tf gamete. both parent produces only one type of gamete

4) TTFF * ttff

	TF	TF
tf	TtFf (PTC taster, unattached earlobes)	TtFf (PTC taster, unattached earlobes)
tf	TtFf (PTC taster, unattached earlobes)	TtFf(PTC taster, unattached earlobes)