8A - Evaluating data on phenotypes Flashcards
What is the phenotype of an organism the result of?
The organism’s genotype and the interaction of its genotype with the environment.
Explain how overeating is influenced by genotype and the environment
1) Overeating was thought to be caused only by environmental factors, like an increased availability of food in developed countries.
2) It was later discovered that food consumption increases brain dopamine levels in animals.
3) Once enough dopamine was released, people would stop eating.
4) Researchers discovered that people with one particular allele had 30% fewer dopamine receptors.
5) They found that people with this particular allele were more likely to overeat - they wouldn’t stop eating when dopamine levels increased.
6) Based on evidence, scientists now think that overeating has both genetic and environmental causes.
Explain how antioxidant is influenced by genotype and the environment
1) Many foods in our diet contain antioxidants - compounds that are though to play a role in preventing chronic diseases.
2) Foods such as berries contain high levels of antioxidants.
3) Scientists thought that the berries produced by different species of plant contained different levels of antioxidants because of genetic factors.
4) But experiments that were carried out to see if environmental conditions affected antioxidant levels found that environmental conditions caused a great deal of variation.
5) Scientists now believe that antioxidant levels in berries are due to both genetic and environmental factors.
What might the data on the relative influence of genes and the environment on phenotype come from?
Twin studies - in particular studies of identical twins.
What can twin studies help determine?
Influences on phenotype.
Why are studies of identical twins 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.
Give example of characteristics that vary due to both genetic and environmental factors
Overeating and antioxidants.
Data that comes from twin studies involving what, is better and why?
Data that comes from twin studies involving a large sample size (i.e. lots of pairs of twins) is better for drawing valid conclusions than data based on a small sample size.
That’s because a large sample size is more representative of the population.
