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We have had an on going debate regarding genetics at my house. Could you please explain what the possible genetic outcomes are when direct cousins marry?


I have been under the assumption that this causes a higher likelihood of genetic diseases because the children of such a marriage will have double genes. (We are already aware of some of the illnesses that run in this particular family, heart disease, diabetes, mental illness, and thyroid disorder to name a few.)


Could you please explain this in greater detail? This has caused a lot of heated arguments- I say it amounts to nothing less than incest and is not an acceptable practice, and he says it is just a cultural practice, there is no harm to offspring, and leads to genetic "purity".

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Welcome to Hypography! :)


The word you are looking for is inbreeding.


Inbreeding may result in a far higher phenotypic expression of deleterious recessive genes within a population than would normally be expected.[1] As a result, first-generation inbred individuals are more likely to show physical and health defects, including:


* Reduced fertility both in litter size and sperm viability

* Increased genetic disorders

* Fluctuating facial asymmetry

* Lower birth rate

* Higher infant mortality

* Slower growth rate

* Smaller adult size

* Loss of immune system function


Natural selection works to remove individuals who acquire the above types of traits from the gene pool. Therefore, many more individuals in the first generation of inbreeding will never live to reproduce. Over time, with isolation such as a population bottleneck caused by purposeful (assortative) breeding or natural environmental stresses, the deleterious inherited traits are culled.

Inbreeding - Wikipedia, the free encyclopedia


As you can see, breeding by close family members can result in all sorts of unpleasant effects, especially for the first generation.

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