A9. Evaluating Data on Phenotypes

Question 1

Evaluating data about influences on phenotypes

The phenotype (characteristics) of an organism is …

It’s not always clear how much a phenotype is influenced by genes and how much it’s influenced by the environment

Two examples of the environment affecting phenotypes

Example 1 - Overeating
Overeating was thought to be caused only by environmental factors, like an increased availability of food in developed countries. It was later discovered that food consumption increases brain dopamine levels in animals. Once enough dopamine was released, people would stop eating.
Researchers discovered that people with one particular ________had 30% fewer dopamine receptors. They found that people with this particular allele were more likely to overeat-they wouldn’t stop eating when __________levels increased. Based on this evidence, scientists now think that overeating has both genetic and environmental causes.

Example 2 - Antioxidants
Many foods in our diet contain antioxidants-compounds that are thought to play a role in preventing _________diseases. Foods such as berries contain high levels of antioxidants. Scientists thought that the berries produced by different species of plant contained different levels of antioxidants because of genetic factors.
But experiments that were carried out to see if environmental conditions affected antioxidant levels found that environmental conditions caused a great deal of _________. Scientists now believe that antioxidant levels in berries are due to both genetic and environmental factors.

Answer 1

The phenotype (characteristics) of an organism is the result of the organism’s genotype and the interaction of its genotype with the environment. It’s not always clear how much a phenotype is influenced by genes and how much it’s influenced by the environment

Two examples of the environment affecting phenotypes

Example 1 - Overeating
Overeating was thought to be caused only by environmental factors, like an increased availability of food in developed countries. It was later discovered that food consumption increases brain dopamine levels in animals. Once enough dopamine was released, people would stop eating.
Researchers discovered that people with one particular allele had 30% fewer dopamine receptors. They found that people with this particular allele were more likely to overeat-they wouldn’t stop eating when dopamine levels increased. Based on this evidence, scientists now think that overeating has both genetic and environmental causes.

Example 2 - Antioxidants
Many foods in our diet contain antioxidants-compounds that are thought to play a role in preventing chronic diseases. Foods such as berries contain high levels of antioxidants. Scientists thought that the berries produced by different species of plant contained different levels of antioxidants because of genetic factors.
But experiments that were carried out to see if environmental conditions affected antioxidant levels found that environmental conditions caused a great deal of variation. Scientists now believe that antioxidant levels in berries are due to both genetic and environmental factors.

Question 2

Twin studies (2)

Answer 2

• Studies of identical twins are extremely useful when trying to determine what’s due to environmental factors and what’s due to genetic factors as they are genetically identical, so any differences in phenotype must be entirely due to environmental factors.
• If a characteristic is very similar in identical twins, genetics probably plays a more important role. But if a characteristic is different between the twins, the environment must have a larger influence.

Question 3

Tip: Identical twins have very similar ___________ marks when they are born and in the first years of their life. Different epigenetic changes occur in each twin as they get older. Environmental factors that can affect the ____________(the epigenetic marks that have been added to the entire genome) include ___, physical _________and _______.

Answer 3

Tip: Identical twins have very similar epigenetic marks when they are born and in the first years of their life. Different epigenetic changes occur in each twin as they get older. Environmental factors that can affect the epigenome (the epigenetic marks that have been added to the entire genome) include diet, physical exercise and stress.