One Twin Study and One Adoption Study

Question 1

Why are twin studies used in psychology?

Answer 1

To establish the extent to which behaviours such as aggression are the result of nature (genes) and nurture (environmental influences)

Question 2

How are monozygotic and dizygotic twins compared?

Answer 2

Compared in terms of concordance rates - the probability that if one twin displays behaviour such as aggression, the other twin will also display it

Question 3

Describe MZ (identical twins)

Answer 3

MZ or identical twins come from one egg and one sperm and so have identical genes

their DNA is 100% the same and they are always the same sex

Question 4

Describe DZ (fraternal twins)

Answer 4

DZ or fraternal twins come from two eggs and two sperms and so are non-identical so they can be the same or different sex

they share around 50% of their genes and their DNA is only as similar as that of any siblings

Question 5

What are the differences in concordance rates in MZ and DZ twins?

Answer 5

If concordance rates are higher for MZ twins compared to DZ twins the behaviour is more likely to have a genetic cause rather than an environmental cause

MZ twins share 100%

DZ twins share 50%

Question 6

What are the strengths of twin studies?

Answer 6

Pre-existing data

Large sample sizes

Question 7

What are the weaknesses of twin studies?

Answer 7

Often don’t share same environment

Epigenetic modification

Question 8

Why is pre-existing data a strength of twin studies?

Answer 8

They use pre-existing data from variables such as aggression making the research more ethical because there is no direct manipulation of the twins behaviour

Question 9

Why are large sample sizes a strength of twin studies?

Answer 9

Information for twin studies often taken from twin registries which hold information about thousands of twins and numerous variables

This means that sample sizes are large and more representative

Question 10

Why is the fact that the environment of twins often not the same a weakness of twin studies?

Answer 10

MZ twins, being the same sex are likely to look identical and are often treated more alike then DZ twins producing important environmental differences

Despite this MZ twins don’t share exactly the same environment, even in the womb, so they often develop differently despite identical DNA

Question 11

Why is epigenetic modification a weakness of twin studies?

Answer 11

This means over time, different environmental influences will cause different genes to be switched on and off

Young MZ twins have few epigenetic differences, older ones (50 years old) have over three times the epigenetic differences

Question 12

Why are adoption studies used in psychology?

Answer 12

Because the environment of adoptive children is not the same as that of their biological families

Question 13

How can behaviour such as aggression be assed with adoption studies?

Answer 13

This is done by comparing the children to their biological parent and their adoptive parent and assessing concordance rates

Question 14

What are the strengths of adoption studies?

Answer 14

Remove extraneous variables

Ethical

Question 15

What are the weaknesses of adoption studies?

Answer 15

Selective placement

Unrepresentative

Question 16

Why is the removal of extraneous variables a strength of adoption studies?

Answer 16

If MZ twins are similar, it isn’t clear whether the similarity is due to the same environment or the same genes

In adoption studies, the adopted individual doesn’t share the same environment as their biological parents, therefore, any similarities in behaviour are due to shared genes

Question 17

Why is the study being ethical a strength of adoption studies?

Answer 17

Tends to be quite ethical because there is no direct manipulation of the participant’s behavior

The adoption occurs naturally so the psychologists simply track and measure behaviour

Question 18

Why is selective placement a weakness of adoption studies?

Answer 18

Adoption agencies try and place children with families similar to their birth family and therefore environmental influences may be similar

Such factors may influence development rather than genes

Question 19

Why is unrepresentativeness a weakness of adoption studies?

Answer 19

People who adopt are unlikely to represent the population

They tend to be better educated, have lower rates of mental illness and come from higher socioeconomic groups

Any conclusions from adoption studies about the effects of genes or environment may not be generalisable to the whole population