Uncle Davey wrote:
>
>>
>>Uncle Davey wrote:
>>
>>
>>>Has anyone done any work on this topic?
>>>
>>>It seems to me as though the 'wild forms' of animals tend to have the
>>>dominant characteristics. When a wild boar mates with a pig, the
>>>
> offspring
>
>>>have more the shape of a wild boar, there is no fattening them up like a
>>>domesticated pig, and so the farmers hate when that happens.
>>>
>>>Can we see a general tendency that wild characteristics are dominant and
>>>ones bred in are nore recessive?
>>>
>>
>>Yes, to a degree. Though I'm not sure it accounts for the phenomenon you
>>describe. Recessive mutations most commonly are recessive because they
>>create a non-functional protein, or no protein at all. So in combination
>>with an allele that does create a functional protein, we get a "normal"
>>phenotype. Since there are more ways to break a gene than to fix it,
>>many mutations are recessive. Breeders work with what they get, and
>>sometimes the phenotype produced by rendering a gene non-functional is
>>useful in a domestic animal. Thus many of the differences between
>>domestic animals and their wild ancestors are probably recessive to the
>>"wild type" alleles. On the other hand, many of the traits important to
>>breeders are polygenic and quantitative, and the domestic breed has been
>>assembled slowly by accumulating alleles at lots of loci that push the
>>phenotype all in the same direction. Mixing this with a wild type will
>>push the phenotype toward the mean. If, for example, some character
>>state, call it A in a domestic animal is influenced by 10 loci eac with
>>two alleles A and B, the domestic animal would have a genotype of
>>AAAAAAAAAA, while a wild type would be a random mix of As and Bs,
>>perhaps tending around 50% each, e.g. AABABBBAAB. A first generation
>>hybrid would have around a quarter Bs and might look like a wild type to
>>
>
>>you.
>>
>>
>
> I see. It looks like you're saying yes, but with qualifications.
>
> In humans, blond hair is like a recessive characteristic, and dark hair is a
> dominant one. Is that because humans came out of Africa? Were humans all
> dark haired first, and some became blond later?
Almost certainly.
> And if there's a functional protein in dark hair, why did we lose it, if
> it's functional?
I'm supposing that blond hair is just a by-product of lower melanin
production in general. Any characteristic is useful in some environments
but not in others. Heavy melanin production is good in protecting you
from ultraviolet light, and comes in especially handy in the tropics.
But it also blocks the reaction that makes vitamin D in your skin. So
pigment is a balance between avoiding nasty sunburn and ability to get
that vitamin D. In the great white north, sunburn is less risk than
rickets. Therefore, selection favors pale people.
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