Download Environment and Gene Expression Scientists have learned that

Environment and Gene Expression
Scientists have learned that gene expression (transcription and translation) can be regulated. It is
now clear that not all genes are expressed in every cell, nor are many genes expressed all of the time.
Cells have complex systems that regulate whether or not specific genes are expressed. Expression
depends on the cell’s need and environment.
Through gene regulation, a given sequence can be expressed in different ways - in different bodies
or tissues, under different conditions, or at different times. Thus, gene regulation accounts for changes
during development as well as differences among organisms that have similar genes. One benefit of gene
regulation is that cells can use energy and materials efficiently.
Recall that many steps take place in the expression of a gene. Also, other molecules play a role in
the processes. Because complex interactions happen at each step, there are many opportunities to
regulate gene expression. So, nearly every step in the process of gene expression can be regulated or
controlled. A molecular system that controls the expression of a specific gene is called a genetic switch.
Like a light switch, a genetic switch can be turned “on” or “off.” Often, the switch is triggered by the
factors or conditions outside the cell. Also, the product of one gene may serve to regulate another gene in
the same organism.
The development and expression of an inherited trait can be influenced by environmental factors
such as nutrients, temperature, sunlight, and so on. The relationship between gene expression and
environmental influence can be seen in the following example.
Temperature affects fur color in the Himalayan rabbit. Under normal circumstances, these rabbits
are white with black ears, nose, tail, and feet. (The black fur helps the rabbit absorb more heat in its
extremities.) However, when some of the white fur on a Himalayan rabbit’s back is shaved off and the
area is kept covered with an ice pack, the new hairs grow in black. The change in temperature produces a
change in fur color. Temperature, an environmental factor, altered the expression of the gene.
Another example involves plants. Remember that plants are green because chlorophyll produces a
green color during photosynthesis, a process which requires sunlight. When parts of a leaf are covered
with dark paper, chlorophyll production stops in the area that is covered. Only the exposed part produces
chlorophyll, is green, and performs photosynthesis. Again, a change in the environment altered the
expression of the gene.
Stress and nutrition can also affect gene expression. For example, someone who has a tall
genotype may not develop a tall phenotype if his or her growth is stunted by malnutrition.
Copy and complete the following questions in your notebook:
1. What is meant by the term gene regulation?
2. What are some of the environmental factors that can regulate genes?
3. Explain two examples of how environmental factors can influence gene expression.