biological (genetic) explanations

Question 1

inheritance

Answer 1

there is evidence that sz runs in families and is somewhat genetic

Question 2

family studies

Answer 2

• suggest the closer the genetic relationships to someone with sz, the greater the chance of developing it
• gottesman (1978) - the rate in the general population is 1%, the chance of 1st-degree relatives developing it is 12%, if both parents have it there’s a 40% a child of theirs will develop it
• tsuang et al (1990) - 1st degree relatives of someone with sz have a 5-20 x higher risk of developing it

Question 3

twin studies

Answer 3

• if mz twins have a higher concordance rate than dz twins, it suggests a degree of heritability
• gottesman and shields (1972) - concordance rate of 42% for mz and 9% for dz twins

Question 4

adoption studies

Answer 4

• an issue with comparing concordance rates of people in the same family is that they share the same environment
• adoption studies allow us to isolate the effects of environmental and genetic factors
• heston (1966) - compared 47 adopted children with sz mothers and 50 children who lived in the same homes as them. 17% of those with sz mothers and none of the control developed sz. the 47 were also more likely to have other disorders and be involved in crime

Question 5

specific genes

Answer 5

• many genes are implicated in sz, suggesting it is polygenic
• different studies have identified different candidate genes, it appears to be aetiologically heterogeneous (caused by many different genes)
• miyakawa et al (2003) - found those with sz were more likely to have a defective version of a gene PPP3CC
• sherrington et al (1988) - found a gene located on chromosome 5 linked in some extended families with sz
• research implicates different genes - is it one gene of several together?

Question 6

give a strength of genetic explanations
1/1

Answer 6

lots of research support (see above)

Question 7

give a limitation of genetic explanations
1/4

Answer 7

genetic factors can’t be the sole factor as the concordance for mz is only 40-60%, since these are not 100%, genes cannot wholly explain sz. a person may be predisposed to sz making them more at risk. by focusing only on one factor (genes) it takes a biologically reductionist approach, not considering other factors biological or otherwise. using this approach leads to an explanation that doesn’t explain this 40-60% concordance rate

Question 8

give a limitation of genetic explanations
2/4

Answer 8

it is hard to separate nature and nurture in family and twin studies, the shared environment could increase the concordance rate irrespective of genes. high concordance rates between mz twins may be due to them being treated more similarly than dz twins or regular siblings. even mz twins raised apart still share the womb environment before birth. this shared environment could be a confounding variable as we can’t separate genetic and environmental factors

Question 9

give a limitation of genetic explanations
3/4

Answer 9

family studies collect retrospective data by comparing a cross-section of people who are already diagnosed, this can be unreliable as issues in memory and records are likely. prospective studies may be more accurate as they follow people over time and can allow for comparisons before and after the condition occurs

Question 10

give a limitation of genetic explanations
4/4

Answer 10

research into the location of specific genes has not produced definitive results. this makes it impossible to understand the underlying mechanism leading from the genetic risk to the disorder