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I just read this (currently unanswered) Quora quesion:

What should I do? After seven years in a relationship, I just find out that our genotype is AS.

Since I never heard of this before I googled and found this article about genotypes:

Knowing one's hemoglobin genotype before choosing a life partner is important because there may be compatibility issues which could have devastating effects when it comes to conception.

Individuals with sickle cells experience severe pains in body parts where oxygen flow is compromised due to blockage in the blood vessels. Read about sickle cell disease here.

  • AA can marry anybody
  • AS is better off with AA
  • AS and AS, AS and AC are too risky
  • Two sickle cells = avoid conception

Again, I was very confused. I have never heard of such advice about who to marry and have children with before and if it was true I expect it to be a recurring subject in the news (like, e.g., obesity).

Do haemoglobin genotypes matter as this Quora question indicates and this article claim when it comes to procreation?

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    I edited the question because (1) "genotype" refers to the genetic makeup of a cell, so it is trivial that it is important in selecting a partner, so you don't try to date an oak tree. (2) genotypic compatibility of offspring is not required for marriage (except maybe in Montana! (3) we know what happened in the past when people didn't consider it - people got sick with sickle cell disease. – Oddthinking Sep 8 at 14:32
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    These things are a function of evolution. That's how animals "handle it". Sickle cell is correlated with malaria resistance, which helps explain why it's been around for so long, and only along populations that have heavy malaria exposure. – fredsbend Sep 8 at 19:49
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Yes, this is accurate. The Wikipedia article has a good summary of the science, and you can also read this leaflet from the NHS in the UK.

Your question about why this matters so much is a good one, and the answer is really interesting. It turns out that being "AS" (meaning one good gene and one faulty one) makes it very difficult for you to get malaria. So in countries where malaria is endemic people who are AS tend to survive longer, be healthier, and therefore have more children. Of course some of those children will be AA (and thus likely to get malaria), and if two AS carriers marry then some of their children will be SS (and hence have sickle cell disease). But some of them will be AS too, and hence be both healthy and protected from malaria, so this is why the gene continues to survive in the population. In fact if you know the odds of an AA person dying of malaria you can predict the proportion of AS; it spreads in the population until the odds of having an SS child who dies of sickle-cell anaemia matches the odds of having an AA child who dies of malaria.

Outside a malaria zone being AS carries no advantage but being SS continues to be a serious or lethal illness, so the gene dies out whether or not the people in question know what it is; all they know is that in their family tree some of their children are just sickly and short-lived. However in historical times without medical knowledge sickly children were not a rare thing for all sorts of reasons.

There are other genetic defects which can cause serious illness when you inherit one from both parents. They are known as Autosomal Recessive Disorders. Cystic Fibrosis is one of them. However being a carrier ("heterozygous": only one copy of the defective gene) for these has no advantage, so the genes tend to be much rarer and hence the odds of two carriers happening to marry is much lower. The malaria resistance means that people with ancestors from malaria zones are much more likely to have it, and hence it is worth them getting screened. People with other recessive disorders in their family tree will generally have screening and genetic counselling too, but its not worth while for everyone.

I don't know about "a recurring subject in the news". I learned about this at school.

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    Thank you for your answer. I found another article about this that said that S only was common among people with African descendant (and existed, but was rare, around the Mediterranean). I live in Northern Europe, hence I see why I have never heard of it before. – d-b Sep 8 at 15:20
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    It's suspected that the Cystic Fibrosis gene might protect against cholera or typhoid. – Ray Butterworth Sep 9 at 0:49
  • @RayButterworth Interesting. Any references? If so I'll add this to the answer. – Paul Johnson Sep 9 at 8:09
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    See CF - Wikipedia. I looked at it yesterday to confirm that it was true and discovered it is no longer a popular theory. My brain was still back ten or twenty years ago: [CF… and cholera: from membrane transport to clinical practice | Advances in Physiology Education] (physiology.org/doi/full/10.1152/advan.00035.2004) and The cystic fibrosis heterozygote--advantage in surviving cholera? - PubMed - NCBI. But given the 1/25 incidence, the CF gene must have some advantage. – Ray Butterworth Sep 9 at 13:48

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