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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Unfortunately, genetics is fiendishly complicated and there isn’t a very simple answer to this question, because there are many different pathways by which genes can be expressed (or, not expressed.) Part of the reason this is is because genes don’t encode traits directly. Each gene is rather just instructions that tells cells to make a certain protein with a certain shape. That’s it. It’s the complex and interconnected system of proteins all interacting which gives rise to physical traits.
But let’s take a relatively simple example: a gene that encodes for a protein that happens to not do anything. The protein in question should do some function, but the way that this gene instructs cells to make it, it doesn’t work. Now consider another gene that has instructions for a working version of this protein. These two different genes might exhibit the familiar dominant-recessive relationship that you might have learned about in school. This is because everyone gets two versions (called alleles) of most of their genes, one from their mother and one from their father. If you have at least one allele that makes the working protein, you’ll end up with some of the working protein being made in the body. You need to have two copies of the “broken” protein gene in order to end up with none of it. And if only a little of the working protein is necessary to result in some trait being expressed, then the trait can be “dominant,” because only one copy of the gene is plenty to get enough of that protein.
That’s a very simplified example. Many traits are actually controlled by many different genes making many different proteins, so the dominant/recessive relationship is not so clear-cut.
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.
The actual mechanic behind what makes a gene strong or weak eludes me. But certain things can be known about how what kind of genes get passed on.
In general: Good genes are strong and bad genes are weak. Due simply to the probability of evolution. Let’s very simply consider the following case situation: You have a large population with completely random sets of genes of 4 types Good/strong, Good/weak, Bad/strong and bad/weak for every of their features.
People will reproduce between each other without any care. After a few dozen generation you should observe the following: A large amount of the population will show a lot of good genes, either weak or strong and the bad/strong genes will probably have almost disappeared.
Now why does it happens? If any individual of said population has too many Bad/strong genes, they are unlikely to survive long. Which make them unlikely to reproduce. Bad strong genes that can override potentially better option will simply weed themselves out of the system. Contrarily, Good/strong genes on the contrary will increase the probability that you survive and reproduce.
As a result, any bad strong gene will have a tendency to disappear over time, while good strong genes will flourish. Bad weak will mostly survive because they’re hidden. And most of the time, they’ll remain as such unless they match with someone with more bad weak genes and one has to be picked. And even then, it would only become a problem IF there are enough bad genes that are being used to counterbalance all the good genes that work.
So in general: Good genes are strong and bad genes are weak. Exception being in humans where we can survive bad genes and work around them long enough (bad eyesight and glasses) and random mutations. Although, said mutation should weed themselves out naturally if they are too much of a burden again.
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