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How many genes do we share with our mother?

I went to a lecture that talked about the behavior of social insects in terms of their relatedness of genes. For instance, workers were 3/4ths related to each other, so it was in their gene's interest to care for each other instead of having their own, half-related offspring.

However isn't it the case that members of the same species are much more related than 1/2 or 3/4s? I've read that we share anywhere from 95-99% of our genes with chimpanzees. Also I believe I've read (perhaps in Pinker) that we share some 60% of our genes with daffodils.

So when they talk about the relatedness of social insects, and they say it's 1/2 or 2/3 or 1/4, aren't they really talking about the 1% to 5% of genes that are in play in sexual reproduction within the species? In other words, aren't I 97% + 1/2 * 3% related to my sister, assuming human beings share 97% of our genes?

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  • $\begingroup$ I guess the issue is that related is a generic term that can induce confusion without a proper definition. $\endgroup$
    – nico
    Commented Jun 6, 2012 at 7:14

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In evolutionary genetic comparison, you are talking about members within species. They will share almost all genes, because if they didn't they would belong to a different species.

However, within species there exist different versions of the same genes, called 'alleles'. When we say that you are 0.5 related to each of your parents, we mean that statistically, 50% of your alleles should be those which your father has, and 50% of your alleles are those passed down from your mother.

Eusocial insects have different mechanisms. Bee males are produced without fertilisation, meaning that they only have one copy of each bee gene. When the male produces sperm, it only has this one set, so all sperms end up carrying the same set of alleles.

Females on the other hand have the normal double set, with two different versions of each gene. So if you look at one gene, half of the female's egg should have one version and the other half should have the other version. All females of one hive are produced by the same queen and the one male that she mated with. Remember, the male only has one set, so the versions coming from the male are the same in all female offspring.

This means a female's genes are made up of: 50% from the father (these are the same across all females) and 50% from the mother (where half the females have one version and half have the other version). Statistically, this means that looking at one gene, there is a 75% chance that two bees will have the same version of that gene.

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  • $\begingroup$ So it's not only the selfish gene, but also the selfish allele? $\endgroup$
    – user151841
    Commented Jun 12, 2012 at 15:18
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    $\begingroup$ Yes, evolutionary biologists tend to talk about genes when they mean alleles. (Usually because what they are saying goes for both genes and alleles; the 'relatedness' is an exception to that) $\endgroup$
    – Armatus
    Commented Jun 12, 2012 at 15:44
  • $\begingroup$ So in biology, there is gene competition between species, and allele competition within species? $\endgroup$
    – user151841
    Commented Jun 17, 2012 at 16:18
  • $\begingroup$ That sounds possible to me, but I think that's another question which I'm not very confident about. $\endgroup$
    – Armatus
    Commented Jun 17, 2012 at 16:27
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The part that is probably specific to this question is that some species of insects divide their population in the reproducing individuals, that are usually diploid and the working individuals, that are sometimes haploids, meaning they only have one copy of their set of chromosomes. This means that the workers have about half the amount of DNA material compared to reproducing individuals, although they share that copy in full with the diploid individuals.

There are variations of this mechanism in different species. Some species keep the copies but epigenetically "shut down" one of the copies. Others shed specific bits of the genome in the somatic cells. Sometimes this loss of DNA is not perfect, so different parts of the genome are lost just by chance.

We humans don't lose any material at all, we just epigenetically "shut down" one of the X chromosomes in XX individuals -- females.

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