Re: how would we define "kin"?

[Mark P. Line]

Matthew Hare wrote:
> 
> The effect is observed as being strongly father-son oriented. Now my
> knowledge of genetics is not good enough to be able to know if genetic
> similarity is closer between fathers and sons than other less immediate
> family relationships ...

Genetic similarity would have to be greater with the mother than with
the father, all things considered.

Apart from that, you have a "guaranteed" degree of similarity with each
parent in that all but the sex chromosomes always come in pairs (in
non-pathological cases), and you normally get one of each from each
parent. The sex chromosomes come in X and Y flavors -- XX individuals
are considered female and XY individuals are considered male. Obviously,
females get one X chromosome from each parent, while males get their X
chromosome from their mothers and their Y chromosome from their fathers.
Everybody gets their mitochondrial genome  along with the rest of the
egg cell only from their mothers. So in general, ever individual shares
about half its genome with each parent, with the mother's genome a half
a nose ahead.

Siblings can have every chromosome in common or none of them, depending
on which particular chromosomes they wound up getting from each parent
(identical twins have the same genome, of course), but all siblings
share their mother's mitochondrial genome. So without knowing (or
inferring) the genotype you don't know how genetically similar two
siblings are. Maximally, they can be identical even if they weren't born
at the same time; minimally, their nuclear genomes can be as dissimilar
as if they were genetically unrelated (although that's not very probable
-- it's easy to work out the probabilities if you know how many
chromosomes the species has).

This is one of the main reasons, BTW, why I think _knowledge_ of kinship
relations is more important to kinship behavior than actual genetic
similarity.


> As a result I have no idea about whether or not the grouse actually
> recognise their fathers or whether they are just reacting to another bird
> with a high degree of genetic similarity.

I suppose the progeny might have a way of recognizing _phenotypic_
similarity, but I am at a loss as to how an animal might be sensitive to
_genotypic_ similarity.


-- Mark

(Mark P. Line  --  Bellevue, Washington  --  <address@hidden>)




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