Three pairs of genes with two alleles each (A₁ and A₂, B₁ and B₂, and C₁ and C₂) control the height of a plant. The alleles of these genes have an additive relationship: Each copy of alleles A₁, B₁, and C₁ contributes 6 cm to plant height, and each copy of alleles A₂, B₂, and C₂ contributes 3 cm.
What are the expected heights of plants with each of the homozygous genotypes A₁A₁B₁B₁C₁C₁ and A₂A₂B₂B₂C₂C₂?

Question

Three pairs of genes with two alleles each (A₁ and A₂, B₁ and B₂, and C₁ and C₂) control the height of a plant. The alleles of these genes have an additive relationship: Each copy of alleles A₁, B₁, and C₁ contributes 6 cm to plant height, and each copy of alleles A₂, B₂, and C₂ contributes 3 cm.

What are the expected heights of plants with each of the homozygous genotypes A₁A₁B₁B₁C₁C₁ and A₂A₂B₂B₂C₂C₂?

Accepted Answer

Hey, everyone. Let's take a look at this question together. X and Y are two genes which control the length of a leaf and have a cumulative relationship. These genes have two alleles, X one and Y one each contributing three centimeters to the length of the leaf and X two and Y two each contributing two centimeters to the length of the leaf. What will be the leaf length? Having the genotype? X two, X two, Y one, Y two. Is it answer choice? A 11 centimeters. Answer choice, B nine centimeters, answer choice C seven centimeters or answer choice D centimeters. Let's work this problem out together to try to figure out which of the following answer choices is the length of a leaf having genotype X two, X two, Y one, Y two. So some things we know about the alleles in relation to the leaf length is that X one and Y one both contribute three centimeters to the leaf length. And X two and Y two both contribute two centimeters to the leaf length. So when we have the genotype of X two, X two, Y one Y two, which we know that the genes that control the length of a leaf have a cumulative relationship. We know that we are looking at X two plus X two plus Y one plus Y two, which can be translated to two centimeters plus two centimeters plus three centimeters plus two centimeters based on the information of what each all contributes to the length of the leaf. And so we can add two centimeters plus two centimeters plus three centimeters plus two centimeters, which gives us a total of nine centimeters, which is answer choice B the correct answer because when we have the leaf that has the genotype of X two, X two, Y one, Y two, we note that the X two contributes two centimeters. The Y one contributes three centimeters and the Y two contributes two centimeters. So we have two centimeters plus two centimeters plus three centimeters plus two centimeters, which gives us the total of nine centimeters. Which answer choice B nine centimeters is the correct answer for the leaf length. Having the genotype X two, X two, Y one Y two. I hope you found this video to be helpful. Thank you and goodbye.

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Key Concepts

Alleles and Genotypes

Additive Genetic Effects

Calculating Expected Phenotype