Tag Archives: Genetics

Fifty years of twin studies

20 Nov

Nature, perhaps the world’s most prestigious science journal has published “Meta-analysis of the heritability of human traits based on fifty years of twin studies.” Here is the abstract:

“Despite a century of research on complex traits in humans, the relative importance and specific nature of the influences of genes and environment on human traits remain controversial. We report a meta-analysis of twin correlations and reported variance components for 17,804 traits from 2,748 publications including 14,558,903 partly dependent twin pairs, virtually all published twin studies of complex traits. Estimates of heritability cluster strongly within functional domains, and across all traits the reported heritability is 49%. For a majority (69%) of traits, the observed twin correlations are consistent with a simple and parsimonious model where twin resemblance is solely due to additive genetic variation. The data are inconsistent with substantial influences from shared environment or non-additive genetic variation. This study provides the most comprehensive analysis of the causes of individual differences in human traits thus far and will guide future gene-mapping efforts.”


The genetics of coffee consumption

13 Oct

A paper in the journal Molecular Psychiatry reports on six genetic loci linked to coffee consumption. You can find the abstract here. PBS has a good summary.

“Findings published today in Molecular Psychiatry confirm the long suspected belief that genetics determine coffee drinking behavior. Scientists have now pinpointed six new gene variations that are more common in those who gulp down the caffeinated beverage frequently.

That’s in addition to two previously identified genetic variants that each code for biological traits. We now have eight loci on record that account for an underlying propensity to drink coffee.

The large-scale study of 120,000 regular consumers provided researchers at the Harvard School of Public Health and Brigham Women’s hospital with ample data. In analyzing the subjects’ genetic makeup via DNA sequencing and comparing it to self-reported coffee drinking figures, the scientists were able to determine why some people need more of the stimulant than others for optimal caffeine effect.”

Is coffee good for us? Dr. Greger weighs in:

Genetics of math and reading

30 Sep

Yesterday, I blogged about the misuse of the word “proof” by science journalists. Wouldn’t you know it, later, I came across this blog post, which tells us:

“Now, a new study proves that people who are good at reading are also quite naturally talented at math.”

Actually, not really. The study, in and of itself, is quite interesting, but this blogger, apparently relying on an LA Times piece rather than the original paper, gets a number of the details wrong.

You can read the original paper here. The abstract reads:

“Dissecting how genetic and environmental influences impact on learning is helpful for maximizing numeracy and literacy. Here we show, using twin and genome-wide analysis, that there is a substantial genetic component to children’s ability in reading and mathematics, and estimate that around one half of the observed correlation in these traits is due to shared genetic effects (so-called Generalist Genes). Thus, our results highlight the potential role of the learning environment in contributing to differences in a child’s cognitive abilities at age twelve.”

One of the big confusions that accompanies a study like this is the misunderstanding of the concept of heritability. Heritability is not a measure of the percentage of a trait is caused by genes. It is not even an individual level measure of a trait, it is a measure of how much of the variance in a population is genetic.

One of the consequences of this is that heritablity is not fixed, it will be affected by the level of environmental variance. We can see this by a simple thought experiment. Imagine a society with total absolute equality between individuals. In that circumstance, since there would be no difference in environment, heritablity would be one hundred percent. This conclusion, strikes many as counterintuitive but if you contemplate it for a while you will see that this must be true.


Not genes versus environment

20 Dec

Most people think that the question is nature versus nurture. The reality is much much complex and much more interesting.

The current issue of The Observer, a publication of the Association for Psychological Science, includes the following quiz:

  1. Cognitive ability in the industrialized world “is approximately 50% to 70% heritable,” reports the Tucker-Drob team. This means that
    1. 50% to 70% of one’s cognitive ability is attributable to one’s genes.
    2. 50% to 70% of the variation among individuals is attributable to their genes.
  2. The genetic influence on intelligence scores (heritability) is greatest
    1. early in life (for example, at age 3), before varied experiences diverge our life courses.
    2. later in life (for example, at age 50 and beyond).
  3. The genetic influence on intelligence scores is greatest among those
    1. at lower socioeconomic levels.
    2. at higher socioeconomic levels.
  4. Increasing the quality and availability of educational opportunity serves to
    1. decrease the genetic influence on intelligence scores.
    2. Increase the genetic influence on intelligence scores.

You can find the answers here. For a deeper discussion see the original paper.

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