What makes a gene either strong or weak, in terms of expression and chance/s of inheritance? Why are some genes more likely to be passed on than others?
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Hm, this is a tough one, I can’t think of a short answer! I’ll give it a go.
You have two copies of genes in your DNA. These genes have instructions to make proteins that are the tools the cells in your body use to stay alive.
First, some genes do a very bad thing instead of being a useful tool. Having just one copy like this will result in that wrong thing being done. This can result in strong expression.
Second, some genes fail to be a useful tool, but don’t outright cause a bad thing. Having one copy like this is usually mostly OK, because the other copy will still work. Having two bad copies means something you need doesn’t happen properly and you may get sick. Sometimes the bad copy works a little bit, but less well. This can result in a more weakly expressed problem.
Men have only one copy of some important genes. So they have the second problem a bit more often than women. This is why more men are color-blind than women. Some types of baldness also work this way.
Some things about your body, like height, are mostly controlled by a lot of genes that each do a little bit. This usually results in the weakest expression, because one of the genes being different won’t affect the system in a big way.
Usually it’s random which copy of your genes gets passed on to your children. There are things smaller than genes in your DNA that sometimes breaks the machinery that copies your genes, and makes it behave in unusual ways. Usually this is mostly harmless, but sometimes it can break things, and the way they work is a little bit scary.
Even though the genes you pass to your children are mostly random, if the genes you have make you very sick, you might not live long enough to have children, so your genes won’t get passed on at all. If your genes make you healthy, you are more likely to live long enough to have children. So genes that make people sick tend to gradually become less common, but sometimes occur randomly. The balance between these two things is called Hardy-Weinberg equilibrium, and it’s why genes that make us sick don’t get completely eliminated with time.
Very little of our DNA contains genes that our body uses to make useful proteins. There is about 50 to 100 times more DNA that isn’t used to make proteins, and we’re not super sure what all of it is for. Since we don’t understand what a lot of your DNA does, the answers I’m giving you aren’t exact and we may have better answers in the future. So it’s a good idea to ask this question again every 5 years.
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