Twin and Adoption Studies
Identical Twins: genes are the same, called monozygotic (mz) because they develop from one
fertilised egg.
Non-identical twins: dizygotic (dz) twins because they develop from two fertilised eggs , they
share around 50% of genes - similar to siblings.
adoption studies:
Twin Study:
Genetic factors are implicated if children
Twins are compared on a specific trait to
are more similar to their biological parents
see how similar they are.
than their adoptive parents.
If a particular behaviour is entirely genetic
Environmental factors are implicated if the
then we expect the MZ twins to show 100%
reverse is true - genic traits over
concordance.
environmental.
If a behaviour is more genetic than the
Pros:
environment, then we would expect MZ
Advantage of removing the extraneous
twins to show a higher concordance than
variable of environment.
DZ twins.
Environment and biology is not shared.
Pros:
Useful in showing twin studies overestimate
Enables researchers to investigate the
genetic factors.
influence of genes because it is assumed
They prove environmental factors are
that MZ and DZ co-twins share the same
important, whereas twin studies have
environment.
detected a greater role of genetics.
The data holds information about many
Cons:
variables, the sample is large and the data
Children may be adopted to families similar
is most likely to be representative.
to their biological families and therefore
Cons:
environmental influences may be similar.
May overestimate genetic influence. The
Apparent similarities with biological
environment experience of one MZ twin is
relatives may be due to environmental
to a large extent the same as the
similarities rather than genes.
environmental experience of the other.
People who adopt other people’s biological
Similarity can be due to shared
offspring are unusual, so are unlikely to be
environment.
representative of the population.
Broad indication that a
Any conclusions drawn from adoption
behaviour/characteristic has a genetic
studies about the effect of genes verses
origin, but they cannot identify the specific
the environment may not be generalisable
genes involved.
to the population as a whole.
Identical Twins: genes are the same, called monozygotic (mz) because they develop from one
fertilised egg.
Non-identical twins: dizygotic (dz) twins because they develop from two fertilised eggs , they
share around 50% of genes - similar to siblings.
adoption studies:
Twin Study:
Genetic factors are implicated if children
Twins are compared on a specific trait to
are more similar to their biological parents
see how similar they are.
than their adoptive parents.
If a particular behaviour is entirely genetic
Environmental factors are implicated if the
then we expect the MZ twins to show 100%
reverse is true - genic traits over
concordance.
environmental.
If a behaviour is more genetic than the
Pros:
environment, then we would expect MZ
Advantage of removing the extraneous
twins to show a higher concordance than
variable of environment.
DZ twins.
Environment and biology is not shared.
Pros:
Useful in showing twin studies overestimate
Enables researchers to investigate the
genetic factors.
influence of genes because it is assumed
They prove environmental factors are
that MZ and DZ co-twins share the same
important, whereas twin studies have
environment.
detected a greater role of genetics.
The data holds information about many
Cons:
variables, the sample is large and the data
Children may be adopted to families similar
is most likely to be representative.
to their biological families and therefore
Cons:
environmental influences may be similar.
May overestimate genetic influence. The
Apparent similarities with biological
environment experience of one MZ twin is
relatives may be due to environmental
to a large extent the same as the
similarities rather than genes.
environmental experience of the other.
People who adopt other people’s biological
Similarity can be due to shared
offspring are unusual, so are unlikely to be
environment.
representative of the population.
Broad indication that a
Any conclusions drawn from adoption
behaviour/characteristic has a genetic
studies about the effect of genes verses
origin, but they cannot identify the specific
the environment may not be generalisable
genes involved.
to the population as a whole.
