09. RM Twin and Adoption Studies Flashcards
Define nature.
The genes you are born with and how they influence your personality.
Define nurture.
Your behaviour is a product of your social and physical environment.
Define twin studies.
Research that investigates that degree of similarity between sets of twins.
Define adoption studies.
Research that investigates the influence of nature or nurture on a specific trait or behaviour.
Define monozygotic.
Identical twins, share 100% of their genes. Always the same gender as each other.
Define dizygotic.
Non-identical twins, share 50% of their genes (same as siblings).
Define correlation.
A relationship between 2 variables.
Define concordance rate.
-A statistical measure that describes the proportion of pairs of individuals that share an attribute, given that one already possesses this trait. A pair is considered concordant if they both possess an attribute of interest, and discordant if they differ.
-The higher the % the more similar.
Describe a way to find out whether a disorder/behaviour has a genetic component.
See whether it runs in families:
-If relatives of sufferers have a higher than average risk of getting the disorder themselves, then it may be that the disorder has a genetic component.
-However, family members typically share similar environments. Consequently, increase risk amongst close relatives may simply indicate that they are exposed to the same set of environmental risks.
Describe an alternative way to find out whether a disorder/behaviour has a genetic component.
An alternative approach is to do a twin study. This looks at the concordance rate (degree of similarity) of twins with respect to the disorder being considered. Concordance rates means that probability of one twin having the disorder if the other already has it expressed as a percentage.
Describe the theory behind twin studies.
-In a twin study, MZ (identical) and DZ (non identical) twins are compared.
-While MZ twins have a greater degree of genetic similarity than DZ twins, it is assumed that both types of twin pairs grow up in identical environments. This means the only difference between the twin types is their genetic similarity.
-So if we discover that MZ twins have a higher concordance rate, this cannot be because their environments are more similar than those of DZ twins; it must therefore be because their genes are more similar.
-The more genes 2 people share, the more similar their behaviour should be, if the behaviour has a genetic basis.
Apply the twin studies theory of concordance rates to depression in MZ and DZ twins.
McGuffin 1996
-If depression is caused by a gene, we would expect that MZ twins either both have depression or neither have depression.
-So we would expect to find a higher concordance for depression in MZ twins than DZ twins.
-MZ twins have identical genes, if depression is caused by genes, then if they both have the gene they should both have depression.
-DZ twins share 50% of their genes. So one twin could have the gene for depression while the other one doesn’t.
What are the advantages of using twin studies?
-Enables researchers to investigate the influence of genes as researchers assume MZ and DZ twins share the same environment so the only difference is genetic similarity.
-MZ twins offer a unique opportunity to study two people with identical DNA.
-Information is often taken from twin registers which hold data on thousands of twins. This means the same is large and likely to be representative.
What are the disadvantages of using twin studies?
-From the moment of conception there will be environmental differences, even for MZ twins (eg separate placentas). Many genes need an environmental switch and as environments are different MZ twins become more different.
-May overestimate genetic influences as MZ twins have more similar environments than DZ twins.
-Only indicates that specific trait has a genetic origin, twin studies are not able to identify specific genes involved. This means twin studies are a good starting point but further research is required.
What are the uses of adoption studies?
-Allows psychologists to measure whether a behaviour is the result of nature or nurture.
-Groups of adoptees are studied and their behaviour is correlated with their adopted families (share environments) as well as their biological families (share genes).
-Adoptees share no genetic material with their adopted families but have a shared environment.
-They do share 50% of their genes with each biological parent but have no had a shared environment for the majority of their life.
-If the behaviour of the adoptees is strongly correlated with the biological family and is not associated with the behaviour of the adopted family then it could be concluded that the behaviour being studied is caused by a biological component.
