Question

Let P = purple flowers and p = white, and T = tall plants and t = dwarf. Of the 16 possible gamete combinations in the dihybrid cross PpTt x PpTt, how many would be the phenotype white, tall?

-none
-16
-1
-9
-3

Answer 1

In a PpTt × PpTt dihybrid cross, 4 out of the 16 possible gamete combinations will result in the phenotype white, tall plants, as the plant must be homozygous recessive for flower color (pp) and have at least one dominant allele for height (T).

Step-by-step explanation:

In the dihybrid cross PpTt × PpTt, we are looking for the phenotype white, tall plants. To be white, the plant must have the genotype pp, as purple flowers (P) are dominant over white (p). Therefore, we only need to focus on the T locus for plant height, since any combination resulting in pp will be white. Tall plants (T) are dominant over dwarf (t), meaning that for a plant to be tall, it must have at least one T allele. The possible gametes that PpTt can produce, with regards to the color and height, are PT, Pt, pT, and pt.

When we combine these gametes, the combinations that result in white, tall plants are pT × pT, pT × pt, pt × pT, and pt × pt, with only pT × pT and pt × pT giving the desired phenotype (since at least one T is needed for tall plants).

Thus, there are 2 possible combinations for each pT and pt combination, which results in a total of 4 gamete combinations that give the phenotype of white, tall plants out of the 16 possible gamete combinations in a PpTt × PpTt cross.