Twin studies
Epigenetics argues that in order for a behaviour to occur, genes must be “expressed.”
The role of genetics has been researched using twin studies: conducted with both
monozygotic, geneticly identical twins formed from the same fertilised egg which split into
two embryos, and dyzygotic twins, twins that share 50% of their genes, formed from two
fertilised eggs. Monozygotic twins will look alike and will be of the same sex, whereas
dizygotic twins do not necessarily look alike or will be of the same sex. The probability that
the same trait will be present in both members of a pair of twins is known as concordance
rate. The higher the shared genetic makeup, the higher the similarity between the twins:
higher concordance rate. Any heritable trait will be more concordant in identical twins than in
non-identical twins. Concordance rates will be lower in siblings. If the concordance rate for
MZ twins is significantly higher than for DZ twins or siblings, it is likely that there is a
genetic component to the behaviour, however if the concordance rate is high for both MZ and
DZ twins it is may be assumed that environmental factors play a large role in the observed
behaviour.
Kendler conducted a twin study to investigate the heritability level of depression and
whether genetics plays a role in an individual’s depression or if the environment is the only
cause, by using a sample of over 42000 twins from Swedish national twin registry.
The results of this study showed that the average concordance rate for MZ male twins was
31% and for MZ female twins it was 44%. The average concordance rate for DZ male twins
was 11% and for DZ female twins it was 16%. Therefore, the final results were that
depression is estimated to be heritable at 38%. This is because even though monozygotic
twins have the same genes, they are not expressed to the same environmental factors so the
genes will express themselves differently. Dizygotic twins may share the same gene
responsible for the expression of depression but not all twins will share it. Even if zygotic
twins shared the same gene, like monozygotic twins, they may not have been expressed in the
same way because of the environment they were exposed to.
To conclude, the twin study conducted by kendler was able to demonstrate, with the
use of MZ and DZ twins, that even though an individual has the genetic predisposition for
depresion, if they are not exposed to evironmental factors that trigger the expression of that
gene, the trait will not be expressed.
Epigenetics argues that in order for a behaviour to occur, genes must be “expressed.”
The role of genetics has been researched using twin studies: conducted with both
monozygotic, geneticly identical twins formed from the same fertilised egg which split into
two embryos, and dyzygotic twins, twins that share 50% of their genes, formed from two
fertilised eggs. Monozygotic twins will look alike and will be of the same sex, whereas
dizygotic twins do not necessarily look alike or will be of the same sex. The probability that
the same trait will be present in both members of a pair of twins is known as concordance
rate. The higher the shared genetic makeup, the higher the similarity between the twins:
higher concordance rate. Any heritable trait will be more concordant in identical twins than in
non-identical twins. Concordance rates will be lower in siblings. If the concordance rate for
MZ twins is significantly higher than for DZ twins or siblings, it is likely that there is a
genetic component to the behaviour, however if the concordance rate is high for both MZ and
DZ twins it is may be assumed that environmental factors play a large role in the observed
behaviour.
Kendler conducted a twin study to investigate the heritability level of depression and
whether genetics plays a role in an individual’s depression or if the environment is the only
cause, by using a sample of over 42000 twins from Swedish national twin registry.
The results of this study showed that the average concordance rate for MZ male twins was
31% and for MZ female twins it was 44%. The average concordance rate for DZ male twins
was 11% and for DZ female twins it was 16%. Therefore, the final results were that
depression is estimated to be heritable at 38%. This is because even though monozygotic
twins have the same genes, they are not expressed to the same environmental factors so the
genes will express themselves differently. Dizygotic twins may share the same gene
responsible for the expression of depression but not all twins will share it. Even if zygotic
twins shared the same gene, like monozygotic twins, they may not have been expressed in the
same way because of the environment they were exposed to.
To conclude, the twin study conducted by kendler was able to demonstrate, with the
use of MZ and DZ twins, that even though an individual has the genetic predisposition for
depresion, if they are not exposed to evironmental factors that trigger the expression of that
gene, the trait will not be expressed.
