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.
