Feather color in parakeets is produced by the blending of pigments from two biosynthetic pathways shown below. Four independently assorting genes (A, B, C, and D) produce enzymes that catalyze separate steps of the pathways. For the questions below, use an uppercase letter to indicate a dominant allele producing full enzymatic activity and a lowercase letter to indicate a recessive allele producing no functional enzyme. Feather colors produced by mixing pigments are green (yellow + blue) and purple (red + blue). Red, yellow, and blue feathers result from the production of one colored pigment, and white results from the absence of pigment production.
What is the genotype of a pure-breeding yellow strain of parakeet?

Question

Feather color in parakeets is produced by the blending of pigments from two biosynthetic pathways shown below. Four independently assorting genes (A, B, C, and D) produce enzymes that catalyze separate steps of the pathways. For the questions below, use an uppercase letter to indicate a dominant allele producing full enzymatic activity and a lowercase letter to indicate a recessive allele producing no functional enzyme. Feather colors produced by mixing pigments are green (yellow + blue) and purple (red + blue). Red, yellow, and blue feathers result from the production of one colored pigment, and white results from the absence of pigment production.

What is the genotype of a pure-breeding yellow strain of parakeet?

Diagram showing two biosynthetic pathways for parakeet feather color production.

What is the genotype of a pure-breeding yellow strain of parakeet?

Accepted Answer

Hey, everyone. Let's take a look at this question together. The flower color in a plant is produced by the blending of pigments from two biosyn pathways involving three genes which produce three enzymes that catalyze the steps involved in the pathways of pigment production. Flower colors produced by mixing pigments are yellow and purple, pink, red, blue and green flowers result from the production of single colored pigments. While white flowers result from the absence of pigment production, determine the genotype of pure breeding plants that produce red flowers. So from the graphic on the screen that is depicting the enzyme pathways for different pigment colors, we are looking for those red flowers, which we can see that we have enzyme A and enzyme B activity is required to produce that red pigment, which means that we have activity in enzyme A and enzyme B. And we know that we do not have activity in enzyme C because enzyme C is only required in the pathway to produce blue or green pigment. So we have no activity or enzyme C. So only activity in A and B and non in C can be depicted as a genotype having the upper case dominant letters or A and B and those lower case recessive letters for C, since there is no functional enzyme for C thus giving us the genotype of pure breeding plants that will produce red flowers. Which when we look at our answer choices, we can see that answer choice B is the genotype that we're looking for to produce those red flowers. And we know that it is not answer choice AC or D because answer choice A would only produce those pink flowers. Answer choice C would only produce those blue flowers and then answer choice D would only produce white flowers. So answer choice B is the only genotype here that produces red flowers, making it the correct answer. I hope you found this video to be helpful. Thank you and goodbye.

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Key Concepts

Genotype and Phenotype

Dominant and Recessive Alleles

Biosynthetic Pathways