Video Transcript
Which of the following best defines
the term complementary genes? (A) Complementary genes are genes
that inhibit the production of complement proteins. (B) Complementary genes are genes
that are simultaneously expressed in the phenotype. (C) Complementary genes are two or
more different genes that work together to contribute to a particular trait. Or (D) complementary genes are
genes that “mix” together to produce a new, distinct phenotype.
This question asks us to define the
term complementary genes, but let’s start by recapping what a gene actually is.
A gene is a section of DNA that
contains the information needed to produce a functional unit, for example, a
protein. Each organism contains many
different genes coding for different proteins. For instance, some of the genes in
your body determine what eye color you will have. But what are complementary
genes? Let’s take a look at an example to
find out.
Sweet pea plants can have purple
flowers, or they can have white flowers. The flower color in sweet pea
plants is controlled by two genes, which we will refer to as gene P and gene C. For the purple trait to be
displayed in the flowers, dominant alleles for both gene P and gene C must be
present. But why?
Here we have demonstrated that gene
C codes for enzyme C. The role of enzyme C is to catalyze
the reaction that converts a colorless precursor into another colorless
precursor. So far, no purple flowers. Here, we have demonstrated that
gene P codes for enzyme P. And the role of enzyme P is to
catalyze the reaction that converts the second colorless precursor into the purple
pigment.
So we can see from our simplified
diagram that we have two different genes, gene P and gene C, contributing to the
expression of a particular trait. In this case, the trait is purple
flowers.
Looking back at our answer choices,
we should now be able to determine that the correct answer is (C). Complementary genes are two or more
different genes that work together to contribute to a particular trait.
