Download 4) Genetics evaluation

Genetic Explanation
Continued….
What are MZ twins and what are DZ twins?
• MZ (monozygotic) twins are identical twins who share
100% of their genetic make-up
• DZ (dizygotic) twins are non-identical twins who share
50% of their genetic make-up, like ordinary brothers
and sisters
What does “concordance rate” mean?
• Concordance rate means the presence of the same
trait in both members of a pair of twins, or the
probability that one twin will have a certain
characteristic (schizophrenia) if the other twin does.
Why do we use twin studies to test the
genetic explanation?
• We use twin studies as MZ twins and DZ twins are
brought up together (in more cases than not). The
pairs therefore share the same environment.
• The difference between MZ and DZ twins is that MZ
twins share 100% of their genes, and DZs only 50%,
thus if MZ twins have higher concordance rates, we
can be sure there is a genetic component to
schizophrenia.
If concordance rate is 100%, what does this
mean?
• If concordance rate for schizophrenia is 100% it means
that if one MZ twin has schizophrenia, the other twin
will definitely have it too
• Therefore, we can conclude that genetics is the sole
cause of the disorder
If concordance rate for MZ twins is
higher than for DZ twins, what does
this mean?
• If concordance rate is higher in MZ twins, because
they are genetically identical, it means that there is a
strong genetic component to schizophrenia
• However, if it is less than 100%, genetics can’t be the
only factor involved.
Why do we use adoption studies to study the
genetic explanation?
• The problem with twin studies is that MZ twins may
be treated more similarly than DZ twins as they are
identical (dressed the same etc.) so we can’t be sure
that it isn’t the environment causing the higher
concordance rates.
• Adoption studies separate genes from the
environment:
• Schizophrenic adopted child – if biological (real)
mother is also schizophrenic, its genetic, if adopted
parent is also schizophrenic, it’s the environment.
Overall, what have we concluded?
• That there must be a genetic component to schizophrenia as
concordance rates are higher for genetically identical (MZ) twins
than DZ twins.
• Also, in adoption studies, we are more likely to develop
schizophrenia if our biological (real) rather than adopted parents
have the disorder
• BUT – not 100% concordance rates and not all children with
schizophrenia in the family develop the disorder so must be other
factors involved
Evaluation of the genetic explanation
• In small groups you have been given 1 or 2 evaluative
points to focus on
• Discuss what these points could mean and produce a
small paragraph on each
• Remember, evaluation marks are worth double the
description marks so you need to be able to produce
a detailed response to each theory or treatment that
we look at
• FEEDBACK TO REST OF CLASS
Predisposition, not cause…
• If you have a certain gene/schiz runs in the family then you may be
susceptible to getting schizophrenia
• However, it is not the sole cause of schizophrenia – other factors must
interact with the genes
Diathesis Stress Model
Individuals are seen as inheriting different levels of
genetic predisposition/susceptibility to developing
schizophrenia
Environmental triggers (such as trauma or child abuse)
then determine if individuals go on to develop
schizophrenia or not.
Methodological issues
• Small sample size so not a representative sample – low
generalizability
• Finnish study – low population validity
Reductionism
• The genetic explanation is reductionist because it reduces a complex
disorder to solely being down to genes, ignoring other factors which
may have caused schiz such as the environment
Determinism
• The genetic is explanation is deterministic because its saying that you
are going to get schiz because of your genes and there is nothing you
can do about it. Ignores free will and that you can make a healthy
environment for yourself