Comments on: Me & my 0.55 brother against my 0.45 brother

By: BDoyle

BDoyle — Wed, 05 Sep 2012 22:01:34 +0000

I might be tempted to call inclusive fitness more of a blunt instrument rather than a Swiss Army knife. How well could someone actually estimate from phenotype how genetically similar he is to a sibling? Might be interesting to do a test and find out. In practice, I think that kin preference would have to rely on some easy-to-apply proxy for relatedness (like being raised in the same litter), that *usually* works, rather than some detailed process to determine precisely how close you are genetically.

By: pconroy

pconroy — Wed, 05 Sep 2012 18:06:37 +0000

Of my 3 kids, they are like their grandparents in the following proportions – overall:

1. PGF 62%, PGM 38%

2. PGF 47%, PGM 53%, MGF 55%, MGM 45%

3. PGF 46%, PGM 54%, MGF 42%, MGM 58%

Where P=Paternal, M=Maternal, GF=Grandfater, GM=Grandmother

For specific traits like Immune System genes, they are:

1. PGF 100%, PGM 0%

2. PGF 0%, PGM 100%, MGF 0%, MGM 100%

3. PGF 0%, PGM 100%, MGF 0%, MGM 100%

So somehow my 2 youngest have an entirely different immune system that my eldest??

By: Razib Khan

Razib Khan — Wed, 05 Sep 2012 17:39:24 +0000

#4, thanks. forgot to put the links up. that’s what i usually do.

is the brother you share more DNA with the brother you have similar politics to?

no. in fact, the one i physically resemble the most (and personality too) has slightly less relatedness. though the difference is not much.

one has to look at single QTLs or genes and their “relatedness” is always either 1 or 0. I hope this makes some sense.

i think sibling rivalry would be due to polygenic effects. so i think overall genomic similarity is probably more important.

By: Julia

Julia — Wed, 05 Sep 2012 17:27:14 +0000

Intersting, but of course, the 0.55 only describe the probability of having sequences in common, but wether a certain gene or not is present would be what counts insuch a sibling rivalry situation. Or, posed differently, the approximation of relatedness derived from a pedigree is an average for all genes or QTLs, while in this context, one has to look at single QTLs or genes and their “relatedness” is always either 1 or 0. I hope this makes some sense.

By: Jeremy Leipzig

Jeremy Leipzig — Wed, 05 Sep 2012 17:19:24 +0000

It is considered good form to cite your figures,

Visscher PM, Medland SE, Ferreira MAR, Morley KI, Zhu G, et al. (2006) Assumption-Free Estimation of Heritability from Genome-Wide Identity-by-Descent Sharing between Full Siblings. PLoS Genet 2(3): e41. doi:10.1371/journal.pgen.0020041

By: M. Möhling

M. Möhling — Wed, 05 Sep 2012 14:13:36 +0000

OT, @April:
> we move every two years to another part of the world,
> which is rough on a kid’s sense of place and belonging
From personal experience I strongly advise against it, so does a Canadian study. I enjoyed moving and traveling as a child, but had to find out later that it takes a toll.

By: Karl Zimmerman

Karl Zimmerman — Wed, 05 Sep 2012 12:45:17 +0000

Out of curiosity Razib, is the brother you share more DNA with the brother you have similar politics to?

Assuming that genes which affect personality traits are fairly evenly distributed around the genome, overall genetic similarity should track closely with personality similarity between siblings. And studies have suggested that friendships tend to form between those who have similar levels of Agreeableness, Extraversion, and Openness. Hence, it could be a valid hypothesis that sibling relationships would also be stronger among those sharing a greater than average amount of DNA.

By: April Brown

April Brown — Wed, 05 Sep 2012 12:17:51 +0000

This really makes me wish I could convince all the relatives my husband and I have in our parents’ generation to do DNA typing – I think this would be really neat way for our kids to think about where they came from (especially because we move every two years to another part of the world, which is rough on a kid’s sense of place and belonging). Alas, most of them find this sciency stuff to be irrelevant or sinister, depending on how republican they are.