This and the next blog are notes from the Coursera: ’Genes and the Human Condition’, University of Maryland, lectures on “My Genes Made Me Do It”.
The age old debate of nature vs nurture takes on new meaning in the light of modern genetics and neuroscience. Society’s misunderstanding of some of the implications genetics goes from one extreme where in 2009 a murderer in Italy got a reduced sentence because he had genes associated with criminality while in the US an argument was made for a higher sentence based on the prosecution’s evidence that people with particular genes cannot be cured. The gene in question was the SRY gene carried on the Y chromosome that determines maleness. There is NO GENE for criminality. Apart from the rare exceptions such as the gene for sickle cell anaemia which protects against malaria and Huntington's disease, a neurodegenerative disorder, all other traits involve hundreds of genes and the interaction with the environment (the nurture bit).
Most of the studies on the effect of the environment comes from the work with identical and fraternal twins. If one minimises the influence of the environment then the remaining differences become genetic. The paradox is that the more equal we make society, the more important we will make the genes.
Professor Raymond St. Leger presented such an example using IQ:
“Present studies indicate that the heritability of intelligence, judged largely by IQ scores goes up linearly across lifespan. So from 30% in very young children, to 40%, 50%, 60%, some people even say it becomes 80% heritable by the time you're middle aged. Well that's saying that 80% of the reason that we're all different in IQ is genetic and so it suggests that genes play a majority role in IQ scores. But environment is important, particularly in young people. Remember that an average IQ is 100. So potentially the 30% of variation in IQ due to environment could be fairly significant in determining if someone has an IQ of 120, or is in the sub-normal range. However, by the time an adopted child is 18, their IQs correlate with their biological parents, and not their adopted parents. This makes the point that the environment, all that mass coaching and tiger mothering can maybe have an effect on the kid's IQ when he's young, bump him up a few notches. But as he gets older, his IQ will become ever more closely correlated with that of his blood relatives.”
The analysis of human traits has moved from using SNP’s (single nucleotide polymorphism)— a kind of barcode to the sequencing of the whole genome. This allows for genome-wide association studies (GWAS). In which tens of thousands of people are analysed for genetic variance — this also uses the non-coding parts of the DNA as well.
What are some of the highlights so far?
It turns out that some of the common conditions such as asthma and diabetes are controlled by tens or even hundreds of genes. The good news is that the pathways by which some diseases start have been identified and some entirely unexpected new pathways have been discovered. For instance a high risk version of the FTO gene has been associated with obesity and the high production of the hormone called ghrelin which makes people hungry. The study of the DNA of centenarians (people called the wellderly) have identified 5-6 biochemical pathways that are often revved up. This includes gene variants of the insulin IGF-1 pathway. As already mentioned variance of the SRY gene has been linked to violent crime.
From the twin studies a risk loci has been identified that is shared by the five major psychiatric disorders: schizophrenia, bipolar disorder, autism, major depression and ADHD. Two of these loci involve genes that are part of the calcium channels — which are used when neutrons send signals in the brain.
For a mash-up of the first set of lectures: