Suppose a polygenic system for producing color in kernels of a grain is controlled by three additive genes, G, M, and T. There are two alleles of each gene, G₁ and G₂, M₁ and M₂, and T₁ and T₂. The phenotypic effects of the three genotypes of the G gene are G₁G₁ = 6 units of color, G₁G₂ = 3 units of color, and G₂G₂ = 1 unit of color. The phenotypic effects for genes M and T are similar, giving the phenotype of a plant with the genotype G₁G₁M₁M₁T₁T₁ a total of 18 units of color and a plant with the genotype G₂G₂M₂M₂T₂T₂ a total of 3 units of color.
Two trihybrid plants are mated. What is the expected proportion of progeny plants displaying 9 units of color? Explain your answer.

Applied to the study of the human genome, a goal of GWAS is to locate chromosome regions that are likely to contain genes influencing the risk of disease. Specific genes can be identified in these regions, and particular mutant alleles that increase disease risk can be sequenced. To date, the identification of alleles that increase disease risk has occasionally led to a new therapeutic strategy, but more often the identification of disease alleles is the only outcome.

What personal or ethical issues arising from GWAS might be of concern to physicians or to those who might carry an allele that increases disease risk?

Suppose a polygenic system for producing color in kernels of a grain is controlled by three additive genes, G, M, and T. There are two alleles of each gene, G₁ and G₂, M₁ and M₂, and T₁ and T₂. The phenotypic effects of the three genotypes of the G gene are G₁G₁ = 6 units of color, G₁G₂ = 3 units of color, and G₂G₂ = 1 unit of color. The phenotypic effects for genes M and T are similar, giving the phenotype of a plant with the genotype G₁G₁M₁M₁T₁T₁ a total of 18 units of color and a plant with the genotype G₂G₂M₂M₂T₂T₂ a total of 3 units of color.

How many units of color are found in trihybrid plants?

Suppose a polygenic system for producing color in kernels of a grain is controlled by three additive genes, G, M, and T. There are two alleles of each gene, G₁ and G₂, M₁ and M₂, and T₁ and T₂. The phenotypic effects of the three genotypes of the G gene are G₁G₁ = 6 units of color, G₁G₂ = 3 units of color, and G₂G₂ = 1 unit of color. The phenotypic effects for genes M and T are similar, giving the phenotype of a plant with the genotype G₁G₁M₁M₁T₁T₁ a total of 18 units of color and a plant with the genotype G₂G₂M₂M₂T₂T₂ a total of 3 units of color. Suppose that instead of an additive genetic system, kernel-color determination in this organism is a threshold system. The appearance of color in kernels requires nine or more units of color; otherwise, kernels have no color and appear white. In other words, plants whose phenotypes contain eight or fewer units of color are white. Based on the threshold model, what proportion of the F₂ progeny produced by the trihybrid cross in part (b) will be white?

Explain your answer.

Applied to the study of the human genome, a goal of GWAS is to locate chromosome regions that are likely to contain genes influencing the risk of disease. Specific genes can be identified in these regions, and particular mutant alleles that increase disease risk can be sequenced. To date, the identification of alleles that increase disease risk has occasionally led to a new therapeutic strategy, but more often the identification of disease alleles is the only outcome.

What is the value of being able to identify alleles that increase disease risk for a person who is currently free of the disease but who is at risk of developing the disease due to its presence in the family?

Suppose a polygenic system for producing color in kernels of a grain is controlled by three additive genes, G, M, and T. There are two alleles of each gene, G₁ and G₂, M₁ and M₂, and T₁ and T₂. The phenotypic effects of the three genotypes of the G gene are G₁G₁ = 6 units of color, G₁G₂ = 3 units of color, and G₂G₂ = 1 unit of color. The phenotypic effects for genes M and T are similar, giving the phenotype of a plant with the genotype G₁G₁M₁M₁T₁T₁ a total of 18 units of color and a plant with the genotype G₂G₂M₂M₂T₂T₂ a total of 3 units of color.

Assuming the threshold model applies to this kernel-color system, what proportion of the progeny of the cross G₁G₂M₁M₂T₂T₂xG₁G₂M₁M₂T₁T₂ do you expect to display colored kernels?

New Zealand lamb breeders measure the following variance values for their herd.

Calculate the broad sense heritability (H²) and the narrow sense heritability (h²) for each trait in this lamb herd.