twin studies

Question 1

what is nature?

Answer 1

-this refers to the biological causes for behaviour
-this means the influence of genes that have been inherited from biological parents

Question 2

what is nurture?

Answer 2

-this refers to the environmental causes of behaviour
-this means the importance of upbringing, regardless of who the parents are

Question 3

what is a twin study?

Answer 3

where twins are compared on a specific trait to see how similar they are

Question 4

what are monozygotic twins? MZ

Answer 4

• identical twins
• they share 100% of their genes

Question 5

what are dizygotic twins? DZ

Answer 5

• non-identical twins
• they share 50% of their genes (like any other siblings)

Question 6

what is a concordance rate?

Answer 6

if we are studying a behaviour which is all or nothing (e.g. whether someone has been diagnosed with schizophrenia or not) we use a concordance rate which is the percentage of those studied are concordant (similar)

Question 7

what 2 things are used to measure twin studies?

Answer 7

correlation and concordance

Question 8

what is concordance

Answer 8

similarity

Question 9

what is the extent to which behaviour is like between twins?

Answer 9

-the extent to which behaviour is the same between twins
-so for example, if one twin is aggressive, the chance of the other twin being aggressive too is highly likely

Question 10

if a particular behaviour is entirely genetic then what do we expect the concordance rate to be like for MZ twins?

Answer 10

100% concordance rate

Question 11

if a particular behaviour is more genetic than environmental would we expect MZ or DZ twins to show a higher concordance rate?

Answer 11

MZ (identical)

Question 12

give 2 strengths of twin studies

Answer 12

• results of twin studies have helped in the prevention of vulnerable disorders e.g. schizophrenia
• they have high ecological validity, as the studies are natural experiments due to the high biological relations in twins

-Enables researchers to investigate the influence of genes because it is assumed that both MZ and DZ twins share the same environment. The only difference between the two groups of ppts is genetic. Therefore, if a trait is genetic then MZ twins should show higher concordance rates than DZ twins.

-Although twins are unusual, information for twin studies is often taken from twin registries, which hold data on thousands of twins. This means that there is a possibility for a large sample that is likely to be representative.

Question 13

give 2 weaknesses of twin studies

Answer 13

• twin studies may overestimate genetic influence. MZ twins have more similar environments than DZ twins; they are treated more similarly, spend more time with each other and tend to share friends.
  therefore, some of the estimated similarity is actually due to a shared environment

-Twin studies provide a very broad indication that a behaviour has a genetic origin, but they cannot identify the specific genes involved. A twin study is therefore useful starting point for research, but more recent technologies are required to help us uncover specific genetic influence.

-Early twin studies e.g. Lange (1929) were inadequately controlled and lacked validity as to whether the twins were monozygotic or dizygotic as it was based on appearance and not DNA