Three pairs of genes with two alleles each A1and A2 B1and B2

Three pairs of genes with two alleles each (A₁and A₂, B₁and B₂, and C₁and C₂) control the height of a plant. Suppose that the 1 allele is dominant in each case and the 2 allele is recessive. Under this revised scheme, the dominant phenotype contributes 5 cm to expected height and the recessive phenotype contributes 3 cm. Assume a baseline height of 15 cm. For all answers, just give the number and not the units. For example, if your answer is 1 cm, just type 1 into the answer box.

What is the expected height of a plant that is homozygous for 1 alleles at all three loci?

What is the expected height of a plant that is homozygous for 2 alleles at all three loci?

What is the height of the F1 progeny of these homozygous plants?

Solution

Assuming that A1, B1 and C1 are dominant and A2, B2, and C2 are recessive.

Data given: dominant phenotype contributes 5cm and recessive phenotype contributes 3cm.

Baseline height to start with:15cm

What is the expected height of a plant that is homozygous for 1 alleles at all three loci?
ANS: Homozygous for A1, B1 and C1 which adds 5 cm from each allele.
Hence: 15+5+5+5=30 cm

What is the expected height of a plant that is homozygous for 2 alleles at all three loci?
ANS: Homozygous for A2, B2 and C2 which adds 3 cm from each allele.
Hence: 15+3+3+3=24 cm

What is the height of the F1 progeny of these homozygous plants?
ANS: Since it is a cross between two homozygous plants, where one has only the dominant version of the allele and the other has only recessive, the resulting progeny will be a heterozygous dominant and hence will have all the dominant alleles alongside the recessive ones.
The answer is the same as question 1, which is 30 cm