Twin Studies Flashcards
Twin studies
Method A01
-Twin studies use the presence or absence of disease in twins as an indication of the level of disease causation that can be attributed to an individuals genetic makeup as opposed to their environmental exposures
Twin studies
Twins A01
- Genetically twins can either monozygotic or dizygotic
- Monozygotic twins= considered to be genetically identical as they developed from the same fertilised eg that divided into shortly after conception
- Dizygotic twins= result from two different fertilised eggs, and therefore on average share around 50% of their genes, the same as any other pair of siblings who share the same mother and father
- Twins are said to be concordant for a condition, if both develop the disease of interest
- Twins are said to be discordant if only one twin develops the disease of interest
- If a condition is found to have a greater degree of concordance in monozygotic as opposed to dizygotic twins, the condition is assumed to have a greater genetic component as monozygotic twins share a greater degree of their genes in common compared to dizygotic twins
Twin studies
Concordance A01
MZ concordance is significantly higher than DZ concordance= disorder has a genetic component
MZ concordance is the same or similar to DZ concordance= The disorder is environmentally caused
MZ concordance is 100%= The disorder is genetically caused
MZ concordance is significantly less than 100%= The disorder has a environmental component
Twin studies
Evaluation A03 Validity
Strength-
Twins allow a natural manipulation of the independent variable; MZ twins always share 100% of DNA and DZ 50%, giving the perfect control for genetic inheritance, as well as this they both have the same environmental experience. This also provides control of the confounding variable, meaning a cause and effect conclusion can be established for effect of nature or nurture in a disorder and studied effectively.
Twin studies
Evaluation A03 Reliability (and generalisability)
Strength-
With the increase in number of multiple births, researcher have a larger sample in which to replicate findings of twin studies in many different cultures and nations. Therefore not only improving reliability but also generalisability as there is a large representation of twins in which researchers can test their hypotheses.
Twin studies
Evaluation A03 Validity
Weakness-
The main assumption of twin studies are the level of similarity between the environments of MZ and DZ twins, as both types of twin pairs are born at the same time into the same environment, it is thought that both twins are exposed to the same set of environmental influences, regardless of zygosity. However this can be questions as MZ twins are typically closer than DZ twins, with their parents more likely to dress them similarly and they are of the same sex. This means people often treat them more similarly than those who are DZ twins. This suggest that MZ environments may be more similar to DZ twins and so the environmental assumptions may not hold for DZ twins.
Twin studies
Evaluation A03 Validity
Weakness-
Despite being genetically identical, MZ twins have been found to not be exactly the same, for instance they have different finger prints, one twin is typically larger and more robust than the other. Therefore, it may not be reasonable to assume that if a disorder had a genetic element, both twins would have it.
