How does inbreeding in humans cause birth defects?
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Imagine you have a few flavors of ice cream. Now, each time you go get the ice cream, you mix different flavors, creating new flavors with a random chance that that new mix of flavors produces a never before seen flavor (genetic mutations which fuel evolution). Now, imagine you just mix two flavors of same/basically same kind. You’d get the same flavor. The problem arises that in case of mixing same flavors here, you aren’t getting any new flavors, quite the opposite, the flavors gets more and more concentrated, so if your recipe had any issues, those issues are just going to become worse and worse the more of same flavor you add.
Not an expert on the topic as you can tell but this is as simple as id manage to explain what I got from the topic. Basically, you need genetic variety, for DNA and chromosomes to mix because if you have to similar genes, they cant connect properly and you get all kind of issues. I also mentioned that ‘concentration of flavor’ is bad, for example you can look at Hapsburgs chin. Each new generation of Hapsburgs had progressively worse cases of humongous chins which made them famous because of inbreeding.
Everyone has double the genetic information they need and nature favors healthy genes.
Family members tend to have similar bad genes. Inbreeding leads to less probability that the next generation gets good information.
basically any very small issue gets progressively more pronounced with each iteration without external variety. So a small chance of some illness increases to a larger chance with each generation, defects becomes increasing pronounced, some body part get exponential bigger or smaller, mental issues dial another notch with each generation becomes less varied and denser copies of itself.
Tldr;If you are making salad or soup you want variety of ingredients not same one chopped or reduced down together thicker every batch
The more closely related people are, the more their genetic information is similar, including the bad information (mutations) that can be inherited.
Many genetic disorders require 2 bad copies of the gene in order to have the problem (recessive disorder). In a normal family (one that doesn’t marry cousins, or have the same male impregnate several generations of his own female descendants), the chances of having 2 bad pieces of information (mutated genes) at the same spot are slim.
Bleeding easily (hemophilia) is an example of a disease that has been passed by families marrying too closely (like European royalty). The bad genes are the only ones available to pass on.
Mental defects are also very common in inbred populations (any animal).
-Assuming you know what DNA is.
-DNA is a physical molecule, so it can be damaged by chemicals, energy rays, etc. Because of this, the human gene pool has accumulated all sorts of errors over time running in different ethnicities, families, and individuals. Sometimes these errors are bad enough to ruin an entire copy of a gene (protein recipe) and cause it to produce rubbish instead.
-DNA is passed down from parent to child, so there’s a good chance you inherit the same broken copies of genes that your parents have.
-Fortunately, all of us humans have 2 full copies of DNA, one from each parent. Even if one copy of a parent’s gene is ruined, the odds are that we will have a good one to use from the other parent. So there might not be any serious effects from these genetic errors.
-However inbreeding breaks this, because you’re no longer practically guaranteed a “good” copy of any given gene that might have an issue. You’re suddenly put at far higher risk for getting 2 broken copies of these genes, and therefore suffering from their associated health issues. The more genetically related your parents are, the worse the odds.
Its tied to the concept of Dominant and Recessive gene variants. Each of your genes is a combination of half from your Mom and half from your Dad. For many genes, there can be two variants, or mutations of that half. If you get a Dominant type from EITHER your Mom or your Dad, then its characteristic dominates. Sometimes, undesirable characteristics are carried by the Recessive variant. You only see that characteristic if you get the Recessive variant from BOTH your Mom and Dad.
So, (and this is a made up example), lets say that a certain type of deafness is caused by a particular (recessive) variant. Lets also say that a sister and her brother both carry this recessive variant, but they aren’t deaf, because they also carry the non-deaf Dominant variant. If the sister and brother were to mate, there would be a higher chance of their offspring getting both halves of this gene in the “deaf” (recessive) variant, resulting in a deaf child.
Those would be genetic defects, not birth defects. A birth defect is when something is introduced to the mother than causes the fetus to develop incorrectly. A genetic defect is when the genes in your DNA prevent your body from working or forming correctly.
Your body 2 copies of every chromosome, and as a result 2 copies of each gene (except on the sex chromosome, but we won’t get into that unless you ask). You get one set of those chromosomes from your mother, and another set from your father.
Most of the time, having one damaged copy of a gene isn’t a problem, but having 2 damaged copies is. For example, the gene for hemophilia (a genetic disorder where your blood doesn’t clot properly) if you have a hemophilia gene and a non hemophilia gene, you won’t have hemophilia, but you’ll be a carrier for it (you could pass it down to your children). This is because hemophilia is a recessive gene, just like blue eyes. However, blue eyes aren’t harmful to us, so blue eyes are a lot more common than hemophilia.
Sometimes only having one copy is harmful. Dwarfism in humans is a dominant gene, meaning you only need one copy of it to be a little person. So you could inherit it from only one parent. To continue the comparison from earlier, a dominant gene is like brown eyes. However dwarfism isn’t as common as brown eyes because having 2 copies of the dwarfism gene is actually fatal, so it doesn’t get passed on as frequently.
Now to get into inbreeding. If your parents aren’t related, then you are getting a random set of genes from both parents, it’s unlikely you would get the exact same set twice. However if your parents are siblings, then all of the DNA you would be getting would be coming from your grandparents directly. Ignoring mutations, you would have a 25% chance to get the exact same copy of a chromosome twice, repeat that for all 23 chromosome pairs, and that’s a lot of repeated DNA. That repeated chromosome would include all the same damaged genes twice. If you repeat this process over and over again, there end up being very few different copies of each gene, so if there is a damaged one in there, your kids will almost certainly have it.
It’s equally likely that undamaged genes get passed on to each generation, but almost everyone has damaged genes, and would be capable of passing those on. Your family has those same damaged genes, so a few generations down the line, without mixing in new copies of those damaged genes, the damaged genes start to express themselves.
Peoples DNA contains defects. The benefit to mating with a stranger is that if your DNA has a defect, theirs can be used instead. If their DNA has a defect, yours can be used instead. This ensures that wherever there is a defect in one of the parents DNA, it won’t be passed down to the child because you can just take the ‘good’ DNA from the other parent.
People who are related have very similar DNA, so if there’s a defect in one of you, you can’t just ‘borrow’ the good DNA from the other person because there’s a good chance they have that same defect too. The result of not being able to replace that defect with good DNA is that the defective DNA manifests in the child in some sort of disability.
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