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First Cousins and Marriage
Name: James
Status: Other
Age: 30s
Location: N/A
Country: N/A
Date: August 2004
Question:
It's a genetics concern about my girlfriend's side of
the family. When we first started to date she mentioned that her parents
were first cousins. I was taken back a little, but her good nature
makes up for a lot. She is perfectly fine meaning that she is not physically
or mentally challenged. My parents are not related in any way. In the
future, if we decide to have kids will the chances be greater for birth
defects?
Replies:
Although the closer animals mate in their heritage the more chances there
are for recessive genes that are bad for development and health to occur,
there are many thousands (probably millions) of people in the world who
marry relations closer than we might think wise. I would expect that if a
single generation had a close marriage ("in-breeding") followed by a
generation of "out-breeding" there would be much less to worry about than
successive generations of inbreeding. That said, there is a well-documented
increased risk of still births and birth defects from "consanguineous
marriages". Consanguineous marriages are quite common in India (uncle to
niece usually) and some studies have been done on it...if you do a search on
the issue look up "consanguineous marriages and birth defects" for
example...http://www.indmedica.com/ijcm/index1.cfm?cmid=180
I will put in a word (or words should I say) for love (since the question
did relate to a personal amorous relationship)..."amor vincit omnia"...an
ancient Latin saying...love conquers all
pf
First of all, let's review genetics a little. Remember that you need a copy
of a trait from both parents-ie. you will give one copy and your girlfriend
will give a copy. When these two are paired together, sometimes one
dominates over the other, which means the trait will "show" even if only one copy is
present. The trait that is hidden is called recessive. If each parent
gives a copy of the recessive trait however, there is no trait to dominate over
it and the recessive trait will show. This is why we say that sometimes
traits "skip a generation" (not always true!) or there is a hidden trait in a
family. With that said, let's say that you and your girlfriend were first
cousins (like her parents). IF (and I say IF) there happened to be one of these
recessive traits being carried in people in the family, with every generation
there is a greater chance that two carriers could come together and each
donate a recessive trait. In other words, there is a greater PROBABILITY that
this trait will show up in a close family mating than in the general population.
If there are no traits like these in the family however, the likelihood
that first cousins will have problems is no greater than the general population.
So it depends on a lot of factors. In your case, the fact that your
girlfriend's parents are first cousins shouldn't affect you, because remember you
also have to contribute a copy of the recessive trait. You should also be
aware that certain disease have a high incidence of carriers in the general
population, such as sickle cell trait in Africans, cystic fibrosis in Europeans,
for example. Even if you aren't related, the chance of having a child with
a genetic disorder is a possiblilty. The job of a genetic counselor is to
take a careful family history and counsel couples on their risk based on their
history.
vanhoeck
No. The fact that your girlfriend's parents were first cousins just means that
approximately 1/16th more of her gene pairs are homozygous than the average
person but since apparently none of these genes are harmful, your children
should be OK. Another thing it means is that, if you have children, 50% of
their genes will come from your girlfriend's grandparents but only 25% of their
genes will come from your father's parents (your paternal grandparents) and the
other 25% from your mother's parents (your maternal grandparents).
Regards, Ron Baker, Ph.D.
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Update: June 2012
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