What does it mean when a child born through incest has
1/4 recessive genes?
If both the parents have a recessive gene, the child will either have 2 (a
full set for that characteristic), 1 (half set), or none of that gene.
I suspect that what you're trying to paraphrase is that the child born has
a 1 in 4 chance of having both genes recessive. If both parents have one
dominant (D) and one recessive (R) gene, each one will give either their D
or R, independent of what the other parent gives. So the possible combos are:
|Parent 1 || Parent 2 |
D || R |
D || D |
R || R |
R || D|
In the DR, DD, and RD cases, there is at least one D, so 3 out of 4 cases
the recessive trait will not show up, but in 2 out of 4 cases, the child
will be a carrier (RD and DR). Only in one case out of 4, the child will
have both genes recessive, and likely display whatever characteristic is
contained in that gene.
The terminology is incorrect. Many of the paired genes in many cases are
the same, but they may or may not be recessive. Incest children have high
risk of diseases and conditions that may be harmful since the genes they
are working with are not different enough to off-set these conditions. One
receives one set of chromosomes from each parent and when the parents have
similar genes, the recessive genes that are mutated or genes that represent
bad qualities may be paired with the exact same gene, causing that trait to
be evident. Yes, in most cases, these are recessive genes, but your
question is asking about gene pairing. I suppose that about 25% of the
genes would be the same. Well, that is excluding crossing over.
This was most evident with the royal lines where royalty married royalty
and many were closely related.
If the parents of a child are both carriers of a trait the child has a
one-fourth chance of inheriting the trait. This is true whether the parents
are related or not. The reason incest is bad is because traits tend to run
in families. So if the partners are in the same family more of the family
members will carry the trait and the more likely it is that the child could
Click here to return to the Molecular Biology Archives
Update: June 2012