Genetics Flashcards
Describe the genetic explanation
- Runs in families and may be inherited
- Risk of developing the disorder is higher for individuals who have family members with the disorder
- Studies have shown the closer the genetic relatedness the higher the likely concordance rate for schizophrenia I.e. If one family member has schizophrenia there is an increased risk for other members
- Contemporary views suggest that heredity explains at least 50% of the cause of schizophrenia. The risk to the general public is 1%
- Polygenic - very unlikely there is one individual candidate gene which causes sz but that possessing a certain combination of genes makes you more susceptible to developing it
- Ripke et al found that there are 108 separate genetic variations associated with the risk of schizophrenia
Why are twin studies good to use as evidence for a genetic vulnerability to schizophrenia?
Twin studies offer a unique opportunity to investigate relative contribution of genetic and environmental factors. If monozygotic twins (100% genes) are more concordant than dizygotic twins (50% genes), then this suggests this greater similarity is due to genetic factors.
Name the twin study
Gottesman and Shields
Describe and evaluate Gottesman and Shields twin study
Gottesman and Shields conducted a meta-analysis of 5 studies of schizophrenia in twins.
They found that the average concordance rate between MZ twins was 46% compared to DZ twins which have 14% concordance.
The fact that there is such a difference suggests a strong genetic predisposition for schizophrenia because the likelihood of developing the disorder is closely linked to the degree of genetic relatedness.
If there was no genetic factor, there would be no difference between MZ and DZ twins.
HOWEVER if it was purely genetic the concordance rate between MZ twins would be 100%.
Why are adoption studies used as evidence for genetics?
Because there is difficulty disentangling genetic and environmental influences for individuals who share genes and environment. Adoption studies remove the effects of the environment to see if schizophrenia is purely genetic, as genetically related individuals who are reared apart are used.
Name the adoption study
Tiernari et al
Describe Tiernari’s adoption study
Tiernari found that of 164 adoptees whose biological mothers has been diagnosed with schizophrenia, 7 (11%) also received a diagnosis of schizophrenia, compared to just 4 (2%) of a control group of 194 adoptees (born to non-schizophrenic mothers).
The researchers concluded that these findings ‘decisively confirm’ a genetic vulnerability to develop schizophrenia. The fact that the children had no contact with their biological mothers ruled out the role of the environment and provides strong support for the role of genetics.
EVALUATION
How many evaluation points are there for the genetic explanation?
3
Name and evaluate one strength of the genetic explanation
A strength of the genetic explanation is that there is now very strong evidence from a variety of sources for a genetic vulnerability to schizophrenia.
Evidence from twin studies (Gottesman and Shields) clearly shows how increased similarity leads to an increased risk of the disorder as identical twins (with the same genes) have much higher concordance rates than non-identical twins (with only 50% of the same genes).
Adoption studies show that children of schizophrenics are still at heightened risk of schizophrenia if adopted into families with no history of schizophrenia, therefore removing the environmental factor.
This there is overwhelming evidence that genetic factors go make some people much more people to developing schizophrenia.
This does not mean that schizophrenia is entirely genetic as there are a number of factors in the environment associated with the risk.
Describe one criticism of the genetic explanation to do with rearing
A criticism of the genetic explanation is that common rearing patterns may explain family similarities.
Many researchers now accept that schizophrenia running in families may be more more to do with common rearing patterns or other factors that have nothin to do with heredity. For example, research on expressed emotion has shown that negative emotional climate in some families may lead to stress beyond an individual’s coping mechanism, thus triggering a schizophrenic episode.
This is a weakness of the explanation as it completely ignores the role of environment in the development of the disorder.
Describe a criticism of the biological explanation to do with twin studies
A problem with using twin studies to support the role of genetics is that MZ twins encounter more similar environments.
A crucial assumption underlying al twin studies is that the environment of both MZ and DZ twins are equivalent. So it is therefore assumed that the greater concordance rate for schizophrenia between MZ twins is a product of genetic similarity rather than environmental similarity. However, it is widely accepted that MZ twins encounter more similar environments and experience more identify confusion (frequently being treated as ‘twins’ rather than two distinct individuals) than DZ twins.
Thus some would argue that the difference in concordance rates between MZ and DZ twins reflect nothing more than environment differences that distinguish the two types of twin.
