originally posted by: Temudjin
a reply to: peter vlar
Now lets say a dozen of humanoids shared a trait, and it was incestuous would it give rise to more genetic damage like overgrowth, albinos, blood
diseases, etc. etc. and if that family mated with a better genetic sample ( naturewise ) would the diseases like size etc. pass thru?
Yes, there would be increased genetic diseases, quite specifically, the diseases that would arise from recessive genetic traits. Normally recessive
traits are not expressed and are trumped by dominant traits, except where they appear on both chromosomes, implying that the identical sequence came
from both parents. When identical sequences appear on both chromosomes, we call this homozygosity.
Recessive traits include: nearsightedness, night blindness, color blindness, grey eyes, green eyes, hazel eyes, blue eyes, blonde hair, light hair,
red hair, straight hair, baldness, normal hairline (no widows peak), no dimples, attached earlobes, no freckles, thin lips, susceptibility to poison
ivy, albinism, hemophilia, congenital deafness, deaf mutism and phenylketonuria (PKU) and there are other rare diseases, too.
(so much for Nazi genetics, all those blond haired blue eyed Aryans are not dominant!)
We can use numbers like the 'coefficient of inbreeding' or 'coefficient of relationship' to measure the amount of homozygotic genes as a percentage
over the whole of the individuals genome. While this does not tell us directly about disease rates, it does tell us the effect, in genetic terms, of
different types of inbreeding.
A list of human rates is shown below:
Mating Relationship = Coefficient of relationship (r)
Inbred strain = 99%
Identical twins & clones = 100%
Parent-offspring = 50%
Full siblings = 50%
3/4 siblings or sibling-cousins = 37.5%
Grandparent-grandchild = 25%
Half siblings = 25%
Aunt/uncle-nephew/niece = 25%
Double first cousins = 25%
Great grandparent-great grandchild = 12.5%
First cousins = 12.5%
Quadruple second cousins = 12.5%
Triple second cousins = 9.38%
Half-first cousins = 6.25%
First cousins once removed = 6.25%
Double second cousins = 6.25%
Second cousins = 3.13%
Third cousins = 0.78%
Fourth cousins = 0.20%
(Incest laws usually concern the relationships where r = 25% or more).
Also, the issue of these recessive genetic diseases is negated in a single step where homozygotisms are essentially removed and normal dominant
expression comes to the fore, i.e: a single mating with an un-related person will undo generations of the genetic damage of inbreeding, in the
offspring of that union.
edit on 14/6/2015 by chr0naut because: (no reason given)