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Question Video: Determining the Outcome of Nonfunctioning Genes in Complementary Gene Action Biology

Flowers of sweet pea plants can be purple or white. The diagram provided shows the biochemical pathway that allows the production of purple flowers in sweet pea plants. If a mutation in gene B caused the enzyme it codes for to be nonfunctioning, what would the outcome be?

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Video Transcript

Flowers of sweet pea plants can be purple or white. The diagram provided shows the biochemical pathway that allows the production of purple flowers in sweet pea plants. If a mutation in gene B caused the enzyme it codes for to be nonfunctioning, what would the outcome be? (A) The plant would have purple flowers. (B) The plant would have white flowers. (C) The plant would wilt and die. (D) The plant would have no flowers.

The genes that control flower color in sweet pea plants are described as complementary. But what does this mean? Complementary genes are genes that work together to produce a specific trait or phenotype. In this example, gene A and gene B are working together to produce a purple pigment, which will give the flowers of sweet pea plants a purple color.

Our diagram demonstrates that gene A codes for enzyme A. Enzyme A then catalyzes a reaction which converts one colorless precursor into a second colorless precursor. Our diagram also shows that gene B codes for enzyme B. And enzyme B catalyzes the reaction which converts the second colorless precursor into a purple pigment. So for a purple pigment to be produced, both gene A and gene B need to produce a functioning enzyme.

The question asks us to determine the outcome if a mutation in gene B results in the enzyme it codes for being nonfunctioning. Let’s assume that gene A and therefore enzyme A are functioning as normal. This means colorless precursor 1 is converted into colorless precursor 2. If enzyme B is nonfunctioning, it cannot catalyze the reaction that converts the second colorless precursor into the purple pigment. If the purple pigment is not produced, then the flowers of the sweet pea plant will not be purple. But instead, they will be white.

So using what we now know about complementary genes and flower color in sweet pea plants, we can determine that the correct answer is option (B). If a mutation in gene B causes the enzyme it codes for to be nonfunctioning, the plant would have white flowers.

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