Topic 8—A: Mutations and Gene Expression- 9. Evaluating Data on phenotypes

Question 1

What is the phenotype (characteristics) of an organism as a result of?

Answer 1

The organisms genotype and the interaction of its genotype with the environment

Question 2

Example: overeating

Answer 2

• thought to be caused only by environmental factors, like an increased availability of food in developed countries
• 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
• found that people with this particular allele were more likely to over eat (they wouldn’t stop eating when dopamine levels increased)
• scientists now think that overeating has both genetic and environmental causes

Question 3

Example: antioxidants

Answer 3

• 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 4

Twin studies

Answer 4

• studies of identical twins are extremely useful when trying to determine what’s due to environmental factors and what’s due to genetic factors
• these twins 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