Chapter 21, Problem 9P

Summary Introduction

To analyze:

The genes responsible for the plant height showing additive gene effect; there are three genes that are responsible for the height of the plant - ${\text{A}}_{\text{1}}$, ${\text{B}}_{\text{1}}$, and ${\text{C}}_{\text{1}}$. Each gene has two alleles, one is dominant and the other is recessive, i. e. allele ${\text{A}}_{\text{1}}$, ${\text{B}}_{\text{1}}$, and ${\text{C}}_{\text{1}}$ is dominant over allele ${\text{A}}_2$, ${\text{B}}_2$, and ${\text{C}}_2$ respectively. The dominant genotype for a gene contributes $\text{10}$ cm in plant height, whereas the recessive genotype contributes $4$ cm.

a) Determine the height potential of a plant which is homozygous for all three dominant alleles

(${\text{A}}_{\text{1}}{\text{A}}_{\text{1}}{\text{, B}}_{\text{1}}{\text{B}}_{\text{1}}{\text{, C}}_{\text{1}}{\text{C}}_{\text{1}}$) ?

b) Determine the height potential of a plant that is homozygous for all three recessive alleles (${\text{A}}_{\text{2}}{\text{A}}_{\text{2}}{\text{, B}}_{\text{2}}{\text{B}}_{\text{2}}{\text{, C}}_{\text{2}}{\text{C}}_{\text{2}}$)?

c) Determine the height potential of the F1 progeny of these homozygous plants?

d) Determine the phenotypes and proportions of each phenotype among ${\text{F}}_{\text{2}}$?

Introduction:

According to the Mendelian genetics, two alleles are responsible for the phenotype of the trait in

which the dominant allele exhibits their effect in the phenotype. In the additive gene effect, the

resulting phenotype of the trait has the contribution of many alleles, which results in the variation

in the phenotype of that particular trait. The alleles of each additive gene contribute their own

quantitative value in the phenotype. Therefore, the additive gene effect is the sum of the allelic

contribution across multiple genes. The segregation and independent assortment of the

additive genes produce different genotypes, but their phenotype depends on the sum of

their allelic contribution.