The portal has been deactivated. Please contact your portal admin.

Question Video: Describing How Traits in a Complementary Gene Pathway Can Be Produced 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. Which of the following conditions has to be true for the purple pigment to be produced? [A] Only gene A must be present and functioning correctly. [B] The genes can be absent, but precursors 1 and 2 must be present. [C] The genes can be absent, but both enzymes must be functioning. [D] Only gene A and precursor 1 must be present. [E] Both gene A and gene B must be present and functioning.

02:49

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. Which of the following conditions has to be true for the purple pigment to be produced? (A) Only gene A must be present and functioning correctly. (B) The genes can be absent, but precursors 1 and 2 must be present. (C) The genes can be absent, but both enzymes must be functioning. (D) Only gene A and precursor 1 must be present. (E) Both gene A and gene B must be present and functioning.

This question asks about genetics and requires an understanding of complementary genes to answer correctly. The diagram provided shows how purple pigmentation in the flowers of the sweet pea plant is a two-step process that requires the presence of enzyme A and enzyme B. The bubbles above describe the colors of the flower during each step of this process.

We can immediately eliminate answer (B) — the genes can be absent, but precursors 1 and 2 must be present — because we know that the precursor bubbles in the diagram describe the state that the flower is in and not the genes that are present. We can read from the diagram that genes A and B are necessary for producing the enzymes A and B, respectively. Therefore, we can also eliminate answer (C) — the genes can be absent, but both enzymes must be functioning — because both enzymes would not be present if both genes were absent.

Now let’s take a look at the remaining answers. Answer (A) states that purple pigmentation can occur only if gene A is present and functioning. If gene A is present, that means that the flower will only produce enzyme A, which will convert precursor 1 to precursor 2. However, enzyme B is required for the second step in the pigmentation process. So a flower with only gene A will have precursor 2 and will be colorless. It needs enzyme B to turn precursor 2 to the purple pigment. So answer (A) is incorrect. In answer (D), “Only gene A and precursor 1 must be present” is very similar to answer (A). It also says nothing about the presence of gene B or enzyme B, which is required for the second stage of the pigmentation process. So answer (D) is incorrect.

Gene A and gene B are complementary genes that work together in a two-step process to produce the purple pigment of the flower. Gene A is necessary for the first step, which allows for the next step to happen. Gene B is necessary for the second step. If, and only if, both gene A and gene B are functional, then the purple pigment will be produced. The correct answer is therefore (E). Both gene A and gene B must be present and functioning.

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy.