A unique chance to compare the effects of nature and nurture
A unique chance to compare the effects of nature and nurtureAnalysis: Mark Henderson
It is well known that many health problems, skills and personality traits run in families. People whose parents have heart disease are at higher risk themselves. Children from churchgoing families are more likely to grow up religious. And sportsmen such as Frank Lampard, Stuart Broad and Damon Hill have followed in the footsteps of successful fathers.
Why this happens, though, is difficult to establish. Is it that we take after our parents because we have inherited their genes? Or is it that the way they brought us up, and the environments to which they exposed us, have had lasting influence?
Studies of twins are one of the main ways science provides an answer. They offer natural experiments that allow researchers to compare the effects of nature and nurture in a systematic way.
Some insights have come from separation studies, in which scientists have followed the development of twins given up for adoption and raised in different homes. But as this is rare, the more usual route is to compare identical and non-identical pairs.
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Identical twins occur when an embryo divides in two, so each twin is a genetic clone of the other. Non-identical, or fraternal, twins are conceived when two eggs are ovulated and fertilised, and thus share no more DNA than ordinary siblings. However, as both types share the same womb and family background, comparisons between them can offer important insights into heritability.
Twin studies have established a strong role for genetics in all manner of human traits. For IQ, personality indicators such as extroversion and neuroticism, and even homosexuality, religiosity and political conservatism, identical twins are more similar to one another than fraternal pairs.
Identical twins are also more likely to be concordant for medical conditions such as autism, heart disease, migraine, diabetes and many cancers.
Twin research has also shown, however, that it is rare for genes to work in isolation. It reveals as much about nurture as it does about nature. The concordance between identical twins for IQ, for example, is about 70 per cent. While this is greater than the 50 per cent concordance shown by fraternal sets, it still leaves a big role for the environment.
The virtue of the TwinBank study is that by assembling a database containing ten times more pairs than any other, it will become possible to investigate many more conditions in this way. For research into rare diseases it is necessary to have a registry of hundreds of thousands of twins to be confident of finding enough pairs who are affected.
A resource of this size will also have other benefits. The hunt for genes that influence disease, for example, involves comparing large numbers of people who have a particular condition with healthy controls. It is an advantage to do this in studies of twins: if one twin is used for the original research, the other can then take part to replicate and confirm any findings.
A further opportunity will be to deepen understanding of a concept known as epigenetics, by which the activity of genes is regulated by chemical markings. While identical twins have the same raw DNA code, their epigenetic programming is different, and TwinBank will help scientists to investigate this for clues to disease.
An extract from Mark Henderson’s 50 Genetics Ideas You Really Need to Know, published on April 2 by Quercus
http://www.timesonline.co.uk/tol/news/uk/science/article6005258.ece
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