Three pairs of genes with two alleles each ( A 1 and A 2 , B 1 and B 2 , and C 1

Question

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?

Explanation / Answer

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

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