Question

Suppose you have one plant with the genotype TTPpYy, and another plant that is recessive for all three traits. If you were to cross these two plants, what proportion of the offspring are expected to be dominant for all three traits?

Answer 1

Answer:

16/64 = 1/4

Explanation:

This is a typical trihybrid cross involving three genes T, P and Y. A plant with genotype TTPpYy is crossed with a plant recessive for all traits (ttppyy).

According to Mendel's law of independent assortment, each allele for each gene will get sorted into the following 8 gametes with only 4 different: TPY, TPy, TpY, Tpy, TPY, TPy, TpY and Tpy.

The recessive parent, ttppyy will produce tpy, tpy, tpy, tpy, tpy, tpy, tpy and tpy.

Hence, using a punnet square, 64 offsprings will be produced with only 16 of them heterozygous dominant for the three traits with genotype (TtPpYy). Hence, proportion is 16/64 equivalent to 1/4.