Chapter 19, Problem 10P

Three pairs of genes with two alleles each ( ${\text{A}}_1$ and ${\text{A}}_2$, ${\text{B}}_{\text{1}}$ and ${\text{B}}_2$, and ${\text{C}}_1$ and ${\text{C}}_2$) control the height of a plant. The alleles of these genes have an additive relationship: each copy of alleles ${\text{A}}_1$, ${\text{B}}_{\text{1}}$, and ${\text{C}}_1$ contributes $6$ cm to plant height, and each copy of alleles ${\text{A}}_2$, ${\text{B}}_2$, and ${\text{C}}_2$ contributes $3$ cm.

a. What are the expected heights of plants with each of the homozygous genotypes ${\text{A}}_{\text{1}}{\text{A}}_{\text{1}}{\text{B}}_{\text{1}}{\text{B}}_{\text{1}}{\text{C}}_{\text{1}}{\text{C}}_{\text{1}}$ and ${\text{A}}_2{\text{A}}_2{\text{B}}_2{\text{B}}_2{\text{C}}_2{\text{C}}_2$?

b. What height is expected in the ${\text{F}}_1$ progeny of a cross between ${\text{A}}_{\text{1}}{\text{A}}_{\text{1}}{\text{B}}_{\text{1}}{\text{B}}_{\text{1}}{\text{C}}_{\text{1}}{\text{C}}_{\text{1}}$ and ${\text{A}}_2{\text{A}}_2{\text{B}}_2{\text{B}}_2{\text{C}}_2{\text{C}}_2$?

c. What is the expected height of a plant with the genotype ${\text{A}}_1{\text{A}}_2{\text{B}}_2{\text{B}}_2{\text{C}}_1{\text{C}}_2$?

d. Identify all possible genotypes for plants with an expected height of $33$ cm.

e. Identify the number of different genotypes that are possible with these three genes.

f. Identify the number of different phenotypes (expected plant heights) that are possible with these three genes.