There appears to be a tendency for schizophrenia to run in families. This suggests that genes and biological factors play a role in the explanation of schizophrenia.. The closer the genetic relationship the more likely the people are to share the disorder. Evidence from family studies by Gottesman showed that when both parent are schizophrenic then there is a 46% chance of the child getting it, however, if only one parent had it, it dropped to 16% and dropped to a further 1% when the sibling of the child had schizophrenia. This suggests that a genetic factor is involved. Gottesman also looked at schizophrenics whose father had an identical twin. He found that there was a 17% of being schizophrenic when the father was but he also found that there was also 17% chance of developing the disease when the father’s twin had schizophrenia but the father didn’t.
MZ twins share 100% of their genes; DZ twins share 50% of their genes. If genes are a factor we would expect more identical twins to share the disorder than non-identical. Rosenthal took a case study which had a set of female quadruplets. They all developed schizophrenia although the onset and symptoms were very different. This could have been a result of having a troubled upbringing. This suggests a strong heritable component.
However, most first degree relatives and twins share the same or similar environments so it is difficult to separate genetic and environmental influences. Adoption studies compare people who have been raised in a different environment from their biological relatives. If they have similarities with their biological relatives this should be due to genes. Evidence from adoption studies, such as, Tenari’s study that had a longitudinal study of 155 schizophrenic mothers who gave up their children for adoption. These were compared with 155 adopted children who did not had a schizophrenic mother. Once these children reached adulthood there was a 10.3% chance of developing schizophrenia when...
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