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Biological Explanations of
depression
Learning objectives:
To outline one Biological explanations of
depression
To evaluate one Biological explanations of
depression
1.Genetic explanation
family, twin and adoption
studies
Biological
explanations
of Depression
2.Neurochemical explanation
The monoamine Hypothesis
Genetic explanation
Three types of study
“carried out an important
FAMILY STUDY into the
inheritance of depression
Elliot S Gershon
University of Chicago conducted TWIN
STUDIES which
looked for evidence
that depression is
inherited
Peter McGuffin
Kings College London
Aside from saying that there
could be a genetic basis for
MDD, there isn’t a lot you
can say about the actual
theory – no single gene has
been identified.
Therefore, AO1 marks for
this explanation are earned
by describing the research
findings that support a
genetic link …
method of
researching the
inheritance of
depression is to
carry out
ADOPTION
STUDIES
Paul H Wender
Harvard Medical School
Down to you...
• using Cardwell....
1.Find research evidence for a family, twin and
adoption study.
2. You must summarise each piece of evidence. Focus
on the results!
3. Explain how the study supports the genetic
explanation of depression
Evidence for genetic explanations
study
Evidence
Family
Gershon (1990)- rates of MDD in 1st degree relatives= 7-30%, higher
than population
Oruc (1998)- 3X more likely to be diagnosed with depression if have a
first degree relative with depression.
Weissmann et al (1984)- relatives of people diagnosed b4 20 had 8x
greater chance of being diagnosed than relatives of non-depressed
Twin
Mcguffin (1996)- 46% concordance rate for MZ, 20% DZ
Allen (1976)- MDD, 40% MZ, 11% DZ.
Adoption
Wendler (1986)- biological relatives 8x likely to have depression
compared to adoptive relatives
Mendlewicz et al (1977)- bi polar- 7% in biological- 0% in adoptive=
stronger genetic influence!!
How can you evaluate the research
that you have found?
Twins
studies
A02
Family
studies
Adoption
studies
What is the problem
of relying on family
and twin studies as
support for a genetic
explanation of
depression?
Genetic explanation
Adoption studies
What causes
Wender
“I looked at adoption
studies, because when a
child is adopted, it is taken
away from its home and
family environment …
depression
“Family studies like Gershon’s, and
twin studies like McGuffin’s, can’t say
genes are the only reason for
depression, because they didn’t
separate genes from environment …
“Adoption studies
are an improvement,
because they
eliminate the
influence of the
family environment …
More Evaluation???
• Twin and family studies do not consider
environmental factors in depression, the higher
concordance rate may be due to their shared
environment not shared genetics
• Genetics as a risk factor but depression cant be
entirely down to genetics - not 100% concordance
rate. What does this suggest?
• In twin studies- possibility of researcher may be
bias, assume that second twin has depression
without thorough consideration. Why is this a
problem?
• Sullivan (2000) Few adoption studies have been
carried out and those that have such small sample
sizes. Why is this a problem?
Make sure you elaborate your
A02……..
Develop your
A02 skills……
Possible paragraph layout:
Present your evidence
What does this evidence
suggest
Question your evidence, is it
strong evidence or are
there problems?
This matters
because....................
Support for the Biological approach to depression comes from twin
studies that have looked at the concordance rate of depression between
monozygotic and diyzygotic twins. Twins studies allows us to look at
how depression has developed in twins that share 100% of their genes in
comparison to twins that only share 50%. McGuffin et al (1996) found a
46 % concordance rate with MZ twins in comparison to a 20%
concordance rate with DZ twins. A higher concordance rate in MZ twins
suggest that the similarities in genes has played a role in the development
of depression.
However, we should be cautious when using twin studies as evidence
because most twins (especially identical) have been brought up in the
same environment with the same experiences, so this could play a role in
the development of depression. Therefore it may be their shared
environment which explains the higher concordance rate (not their
shared genes).
Furthermore, if the development of depression was solely genetic then
we would expect to see a concordance rate closer to 100% in identical
twins as the have exactly the same genes, 46% suggests that genes may
be a risk factor but that the environment also plays a role. For example, it
may be that one twin experiences a trauma that the other twin does not
which may lead to only 1 twin developing depression.
The idea that depression has a biological basis matters because it allows
us to consider the role that genes play in the development and treatment
of this mood disorder. For example, the genetic explanations could have
implications for further research such as gene therapy.
Task
• Using the paragraph layout, write your own
‘big mac’ paragraph on either family or
adoption studies.
• Bring in other evaluation points, do not use the
evaluation points on the example
Biological Explanations of
depression
Learning objectives:
To outline one Biological explanations of
depression
To evaluate one Biological explanations of
depression
1.Genetic explanation
family, twin and adoption
studies
Biological
explanations
of Depression
2.Neurochemical explanation
The monoamine Hypothesis
Recap quiz on genetic explanations of
depression
1. Mcguffin carried out a twin study looking at
concordance rates in depression between MZ and
DZ twins. What do we mean by concordance
rates?(1)
2. What did Mcguffin find?(2)
3. Identify one problem with Mcguffin’s study(2)
4. Which studies (twin, family or adoption) provides
the strongest support for the genetic explanation,
explain your reason?(2)
5. Identify one problem with family or adoption
studies.(2)
The neurochemical explanation
• Depression is a result of reduced levels of
certain neurotransmitters (neuro chemicals), e.g:
• Serotonin
• Noradrenaline
• Dopamine
(
Monoamines)
Hence, Monoamine hypothesis
Neurotransmitters
monoamines
serotonin
Dopamine
noradrenaline
Who can explain this
diagram???
Biochemical explanations of Depression
Using your text book, answer the
questions on the worksheet – all
A02
Evaluation points are provided,
your job is to explain and extend
on them
Generic essay structure for
explanations
Important to Conclude!!
Is the biological explanation a full or complete
explanation of depression?
It may be we inherit a genetic predisposition?
Homework
• Discuss two or more biological explanations
for depression. In your evaluation you
should refer to research evidence (24 marks)