from what i heard from older folks (grandparents etc), it was
said that if same surname marry each other, or cousins marry each
other, the child will have a higher risk of being born with some
deficiency / disability etc.
pls lah i just
posted this article........so read it.
From a
genetics point of view, the reason to discourage inbreeding is to
prevent undesirable genetics disorders. Genetic mutations occur in
almost everybody, but the vast majority do not create any medical
problems because the are recessive. Recall that most genes code for
a protein of some sort, and that for most of our genes, we have two
copies, one from each parent (an exception are the X-linked genes,
for which males have only one copy). Thus, if a mutation occurs in
one gene, there is a back-up copy. A person would only show the
effects of missing the protein entirely if both
gene copies carried the mutation. This is an example of a recessive
trait.
In order for a child to inherit two
copies of the mutant gene (in other words, be
homozygous for the mutation) and
therefore have the disease, both parents must be carriers. The odds
of two children of a carrier both being carriers are 0.5 x 0.5 =
0.25. If these carriers marry, their chances of having an affected
child are 0.25. Therefore, the chances of an incestuous union
between two children of a sickle cell anemia carrier giving a child
with sickle cell anemia are 0.25 x 0.25 = .0625, or
6.25%.
But
remember, these are the odds only for one gene. Our hypothetical
ancestor may carry any number of recessive genes that might be
dangerous in the homozygous form
Posted
By: Louise Freeman, Post-doc/Fellow
Biology