Video Transcript
Which of the following statements
is incorrect? (A) The phenotype is the set of
observable characteristics and is the result of genetic and environmental
effects. (B) Environmental changes have no
influence on the expression of genes in living organisms. (C) The environment can affect
morphological and physiological development. Or (D) some drugs and chemicals can
determine which genes are turned on or off.
The phenotype of an organism
describes the observable characteristics of that organism. A human, for example, could have a
blue-eyed phenotype or a green-eyed phenotype. He could also have a taller
phenotype or a shorter phenotype. But what determines the phenotype
of an organism?
A phenotype is determined by the
particular alleles, or forms of genes, an organism has, which is called that
organism’s genotype, and the expression pattern of those genes. Different alleles for a gene will
produce slightly different proteins, which can cause certain differences in
characteristics that would account for different phenotypes.
For example, the differences in eye
color phenotypes can be due to different pigment proteins produced by the different
eye color alleles. An organism’s environment can also
influence the expression of genes. Let’s assume there is a gene that
when expressed at a certain stage of the development of an organism, like puberty in
a human’s development, causes the organism to grow taller. When the person comes into puberty
and has sufficient access to food to fuel the growth, the gene will be expressed and
the teenager grows.
However, if the teenager does not
have access to a sufficient amount of food, the food available will just be used to
sustain general life processes, rather than for growth. This environmental factor can
reduce or even stop the expression of the growth gene, and the teenager will not
grow or will only grow a small amount. So, that person’s phenotype, in
terms of height, is influenced by both the genetic presence of the allele for height
and the environmental effects of the presence of food that may increase or decrease
the expression of this gene. Therefore, (A) is correct, and we
can eliminate it.
Also, as we’ve pointed out, the
environment does have an effect on the development of that person. So (C) is a correct statement, and
we can also eliminate that choice.
Similarly, while presence of food
is one environmental pressure that can affect phenotype, it’s not the only one. Presence of drugs or chemicals in
the environment could also affect the expression of genes. So (D) is also a correct statement
and can be eliminated.
As we have indicated through these
examples, differences in an organism’s environment can affect the way genes are
expressed, for example, whether a tall genotype actually results in a tall
person. Therefore, the incorrect statement
is (B). It is incorrect to say
environmental changes have no influence on the expression of genes in living
organisms.
