Comments on: Genomic noise and individual variation

By: Luke Lea

Luke Lea — Mon, 28 Jan 2008 18:30:17 +0000

So Charles Murray’s point (in the Bell Curve I think) that if we remove all environmental differences, then all the remaining differences would be genetic, is false?

By: omnivore

omnivore — Sat, 26 Jan 2008 21:05:12 +0000

I am very sympathetic to the noise argument. In discussions of the proportion of variance explained in [important variable X], the statement that Y explains 40% of the variance is, in my experience, frequently greeted with the automatic assumption that some more-important causal factor must explain the remaining 60%. Instead, the first question should be what proportion of the variance is explainable at all. If 50% is due to noise, then 40% actually covers 80% of the explainable variance.

Note that estimating the proportion of explainable variance is difficult, often (seemingly) impossible. Reliability coefficients are useless, because variance also arises from non-identity between the measurement and the construct being measured. If one can account for 100% of the variance, that’s the end of the story, but one must not be working in population genetics. A more typical situation is to have factors that cover a minority of the variance. Then…what? I wonder whether a principled way to decide between noise and as-yet-undetected causal factors exists, even in some useful subset of situations.

By: Jon Claerbout

Jon Claerbout — Sat, 26 Jan 2008 17:37:38 +0000

the error term must includes simple stochastic noise on any part of the complex mapping from genotype to phenotype

I see it a little differently.
Let's talk about IQ. It's variation could be regressed against a sum of parental IQ and SES (Socio-Econ-Standard). What better environmental model do you have besides SES? Maybe none, and that one is not measured very precisely. You end up with a big residual even after doing your best to model both the genes and the environment. As I'm a seismologist I can only guess at the numbers, so I'll stop there. The point is, there are lots of sources for errors besides in the gene-->phen transform

By: Daniel Newby

Daniel Newby — Sat, 26 Jan 2008 14:01:33 +0000

This research found that 0.9% of cells in schizophrenic human brains are aneuploid for chromosome 1, whereas only 0.3% were in normal controls. (Aneuploid == gain or loss of a chromosome.)