Srinivas S  wrote in message
news:...
> Why do some cultures allow marriage between close relatives and others
> treat it with great contempt? The usual argument against inbreeding is
> that rare genetic diseases can show up easily in a child which inherits
> harmful recessive genes from both parents. Why is this not applicable to
> those cultures which have been in existence for a long time and allow
> inbreeding? There SEEMS to be apparently no observed phenomenon of high
> incidence of genetic diseases in those communities.

The incidence of inbreeding depression is linked to the frequency of
recessive deleterious alleles segregating in the population under
mutation selection balance.  The equilibrium frequency depends on the
strength of selection, which depends on the frequency of homozygous
versus heterozygous carriers of the deleterious alleles.  Obviously
this depends on the rate of inbreeding.  In other words, inbred
individuals in populations with a long history of inbreeding should be
expected to have a lower reduction in fitness than inbred individuals
in populations with a history of outbreeding.

I'm not sure which communities you are talking about, and have no idea
about what data has been collected on this.  So, although the argument
i have given above is correct, it should not be misapplied to
situations that do not warrant it.

I do know of several communities with high degrees of inbreeding and a
host of common recessive disorders - Amish peoples in the US for
instance - although they are relatively recent, probably derived from
a much larger breeding pool, and so perhaps supports the view taken
above (i.e. inbreeding after a history of outbreeding is especially
bad for fitness).

Hope these mutterings are of some help.
---
þ RIMEGate(tm)/RGXPost V1.14 at BBSWORLD * Info{at}bbsworld.com

---
 * RIMEGate(tm)V10.2áÿ* RelayNet(tm) NNTP Gateway * MoonDog BBS
 * RgateImp.MoonDog.BBS at 5/10/03 8:24:23 PM