Genetic explanations - biological explanations

Question 1

Genetic explanations

Answer 1

• family, twin and adoption studies are used to establish how strong the genetic link is
  
  • evidence that the closer the biological relationship, the greater the risk of schizophrenia developing
    1st degree relatives share 50% of genes

Question 2

Family studies

Answer 2

kendler et al (1985)
- found that 1st degree relatives of those with sz are 18 times more at risk
-suggests that there is a genetic link to the development of sz — risk increases with closer genetic relationship

Gottesman (1991)
- findings show that concordance rate increases if you have a closer genetic relationship
however it is not 100% so there must be other explanations

kety et al (1962)
- the copenhagen high risk study
- 207 children with mothers had sz (high risk)
- 104 children with healthy mothers (control group)
- 16.2% of children in high risk group developed sz compared to 1.9% of the control group — follow up was conducted after 10 years

However 63% of people diagnosed with schizophrenia do not have any family history of sz - shows that other factors may potentially be involved

Question 3

Twin studies

Answer 3

• compare the difference in concordance rates ( the likelyhood of both being affected with the disorder ) between the identical and non identicial tiwns
• only identical twins have identical genes however non identical can be used to distinguish the effects of genetics and environment

Question 4

Twin studies findings

Answer 4

Gottesman and shields found a concordance rate of 42% for identical twins and 9% for fraternal

Torey (1992)
- argue twin studies were inadequate
- found from re-assessing eight studies that concordance rate for identical twins was 26% compared to 6%

Cardno et al found 40% of concordance rate in identical twins compared with 5.3% fraternal

Question 5

Adoption studies

Answer 5

• adopted children who develop sz can be compared with their biological and adoptive parents
• attempt to highlight genetic influence as development of disorder should be maintained regardless of a change in environment

Question 6

Adoption studies findings

Answer 6

Heston (1966)
- compared 47 children of sz mothers who were adopted before the age of 1 month with a control group of 47 children who were raised by non schizophrenic adopted mothers
- 10% of children with sz mothers developed it themselves whereas non of the children from the control group did

Tienari et al (1987)
compared 112 cases of adopted children who had biological mothers who had been diagnosed with sz with 135 adopted children who had non sz biological mothers
7% of these children developed sz compared to 1.5% of the control group
- suggests there must be other explanations other than genetics

Question 7

Sample question - Describe one biological explanation for schizophrenia (10 marks)

Answer 7

Intro - explain how it is assessed by examining family twin and adoption studies
3 paragraphs - outlining the concordance rates from family, twin and adoption studies

twin - concordance rates are much higher with identical twins
adoption - those with adoptive mothers who had sz were more likely to develop sz
family - if those who had first degree relatives with sz then they were more likely to develop it

Question 8

Evaluation

Answer 8

family studies
- concordance rates increase with closer genetic relations however the increase could also be explained by environmental factors, shared experiences and lifestyle choices among individuals
- could also be explained by environmentk

• the same for non identical twins + siblings which would lead to the expectation that concordance rates should be similar — however they are not which suggests

Answer 9

family studies
- concordance rates increase with closer genetic relations however the increase could also be explained by environmental factors, shared experiences and lifestyle choices among individuals
- could also be explained by environmental factors e.g those who are closely related to share similar environments, which can influence the expression of genetic traits — have shared experiences, lifestyle choices and exposure to similar environmental factors can contribute

• the same for non identical twins + siblings which would lead to the expectation that concordance rates should be similar — however they are not which suggests genetics alone do not fully account for the development of this disorder
• if genetics were the main factor then we would expect the concordance rates for schizophrenia to be much higher in identical twins compared to siblings
• can imply environmental factors play a big role

Adoption studies
- children are sometimes adopted by members of their extended family which can cause an issue when trying to establish a genetic link
- this is because some adoptive parents can share some genetic material with the child — can make it difficult to seperate the influence of genetics from that of the environment
- can lead to ambiguous conclusions in studies that aim to clarify the roles of nature and nurture
e.g if the child is adopted by an aunt of uncle they may inherit genetic traits from that relative and it leads to researchers not being able to distinguish if certain behaviours are due to genetic factors inherited from the biological or adoptive relatives