Predicting someone's face: look at their parents

By Razib Khan | September 14, 2012 12:55 am

A few years ago there was a paper out which illustrated that standard Galtonian method of regression of offspring upon parents still predicted height far better than the most modern genomic techniques. The issue is that height is a quantitative trait whose variation is controlled by variants at hundreds, and likely thousands, of loci. Generating a useful prediction for one individual from a “bottom-up” genetic model is daunting because of the overwhelming number of variants. This is in contrast to pigmentation traits, which been found to be well characterized by a few large effect quantitative trait loci. That is, one gene can account for a substantial minority of the variation within the population of the trait. In regards to eye pigmentation in Europeans the majority of the blue vs. non-blue eye color difference can be accounted for by one locus, HERC2-OCA2. Not so for height, intelligence, and now it seems likely, facial morphology.

A Genome-Wide Association Study Identifies Five Loci Influencing Facial Morphology in Europeans. The issue I’m alluding to is found buried in the paper:

Moreover, our data also highlight that the high heritability of facial shape phenotypes (as estimated here and elsewhere), similar to that of adult body height…involves many common DNA variants with relatively small phenotypic effects. Future GWAS on the facial phenotype should therefore employ increased sample sizes as this has helped to identify more genes for many other complex human phenotypes such as height…and various human diseases.

Am I on crack, or are we not going to really get much yield from hunting for specific genes in most cases? Granted, there may be populations like pygmies who are well deviated on some trait, so we’ll put a finger on particular variants which shift the trait value a lot. Additionally, like height I wouldn’t be surprised if we find some evidence for selection on facial morphology related genes. But this seems to dampen the likelihood of robust individual prediction. The limits of forensic genetics? Say it ain’t so!

CATEGORIZED UNDER: Anthroplogy, Genetics, Genomics
MORE ABOUT: Phenotype, Prediction
  • Dwight E. Howell

    A family “look” may last for generations. On the other hand a slightly different shuffle of the genes and it may be completely changed.

  • John Roth

    It looks like an interesting study. The thing that jumps out at me, though, is that facial morphology has a huge number of parameters, while height is a simple linear measure and skin color has a very small number of parameters. It’s also true that a large part of the variation in skin color has to do with the size and number of pigmentation cells, not with different quantities of different pigments.

    I don’t find it surprising that there would be a large number of genes involved with the different aspects of facial morphology; there are an enormous number of possible faces! This doesn’t bode well for forensic prediction in the near term simply because the problem is inherently complex.

    In thinking about it, I wonder whether part of the problem with height is that the apparently simple measure is the sum of a number of different measures that are only partially correlated, and that an approach which examines the different skeletal measurements might bring more clarity to the situation.

  • Grey

    @1
    Marrying cousins might make retaining a family look easier.

    Which might imply face morpholgy could be more related to ROH than individual genes?

    @2
    “wonder whether part of the problem with height”

    I’m wondering if height might not be less the result of a random jumble of genes and more a jumble of genes doing specific but contradictory things e.g.

    1) one set resulting from long-term selection which, all else being equal, would determine the average height of a population.
    2) one set that specifically effects male or female height in opposite directions
    3) one set that increases or decreases height according to nutrition levels
    4) a combined set formed from any of the above with “dents” i.e. the genetic load idea

    The reasoning behind this is nutrition seems to have different effects on different populations e.g. the Dutch, which makes me wonder if populations have tall, short or average genes from past selection which can be suppressed by nutrition and maybe genetic load so when the suppression is lifted one population may shoot up a foot in height while another population it’s only 6″.

    Also does assuming height is beneficial or deleterious change expected outcomes as maybe it can be either depending on circumstances.

  • Karl Zimmerman

    3 –

    You forgot that genes for “height” may refer to different parts of the body. Some could result in overall greater size. Others would result in merely longer legs (upper, lower, or both). Genes regulating brain size would even cause height to be slightly increased, as the apex of the skull would be a bit higher.

  • Grey

    @4 Yes, that could be quite a big deal if there were separate selective pressures applying to legs, torso, skull.

  • Justin Giancola

    “Others would result in merely longer legs (upper, lower, or both)”

    I don’t suppose it works this way; actually, I’ve heard the contrary, that limb segments are related by a particular ratio for normal modern humans.

    I remember seeing observations in physical anth. that tried to validate sapiens/neanderthal hybrids – before DNA proof – by examining leg segment ratios in some ancient fossils.

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Gene Expression

This blog is about evolution, genetics, genomics and their interstices. Please beware that comments are aggressively moderated. Uncivil or churlish comments will likely get you banned immediately, so make any contribution count!

About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at http://www.razib.com

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