Biology - Identical twins
These two identical twins were separated at birth. Click to see the
differences that can occur due to the effects of the environment. Think
about how the environment affects the phenotype.
Identical twins have been studied to try to find out the extent to which
the environment affects the phenotype.  Identical twins have the same
set of coding instructions as each other (genotype)  because they
develop from one cell, they are clones  of each other. There can be
differences, such as height, weight, level of fitness and cultural
interests, due to the effects of their environment, such as diet, exercise
and their experiences. The environment has had an impact on the way the
genotype is expressed. This is especially apparent in identical twins who
have been separated early in life and who have been traced.
Other examples are given below:
* Himalayan rabbits will only develop dark tips to their ears if they are
exposed to lower temperatures; the temperature affects the activity of a
temperature-sensitive enzyme. 
* Plants with the same genotype grow differently in different conditions:
in favourable conditions they will grow to their full genetic potential, at
extremes in their tolerance range, such as very dry or very cold
conditions, they may be stunted.
* The pH of soil affects the colour of petals of cuttings of the same
variety of hydrangea.
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