how do DNA changes get passed to their children, if all eggs are done being formed and already have the genetic material needed in their teen(?) years?
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There is a difference between a heritable and a non-heritable mutation. The cells that give rise to life, egg cells and sperm cells, are called germ cells, while all the other cells in your body are called somatic cells. Mutations in somatic cells are non-heritable, meaning they can not be passed down to offspring. Mutations that occur in the germ cells are heritable, because they CAN be passed down to offspring. So, in order for a genetic mutation to be passed along, the mutation needs to have occurred during gametogenesis, or the formation of the germ cells. So, in short, the mutation occurred waaaaay back when the mother was herself still very young. This also means that, as you correctly guessed, mutations that occur after this point are non-heritable
Hereditary gene mutations are there effectively from the creation of the egg or sperm. A parent that passes a mutation on to their child has almost certainly had that mutation since conception, so it doesn’t matter when a woman creates that egg or man creates that sperm; they have the mutation for life.
In most cases the mother already had the mutation. Because she has a pair of each chromosome (46 chromosomes in 23 pairs), one could be ‘faulty’ and the error could be effectively masked by the other ‘correct’ copy. But when they create an egg only one of each pair goes into the egg. So 50% of them carry the faulty copy.
In other cases the error occurs during the process of creating the egg: when the chromosome pairs split up. one of them can sometimes go off with bits of the other pair. So you end up with two faulty eggs – one has too much dna, one has too little.
Well, one thing is: the mutation can happen in the egg cell itself, even if mom doesn’t have the mutation in the rest of her body (the term for the rest of her body is: her somatic cells).
So I am a woman with a genetic mutation. I was born with it. Something happened when I was an embryo, and there was a mistake made copying some of my DNA. That mistake was copied over and over and over as I developed, sort of like making a photocopy of a page with a smudge on it—all the copies will have that same smudge even if nothing else bad happens to them.
If I have children, my contribution to that embryo will come from an egg that has some percent chance of having been made with that mistake. Unlike normal cell replication, which is a direct photocopy, the process that makes reproductive cells is more like making a copy, tearing it up, and then collecting half the pieces somewhat randomly. So those reproductive cells aren’t guaranteed to have the part of the photocopy that was smudged. Some may have, but some may not. If the embryo is made with one of the eggs that has a bad copy, then the resulting child will have the same genetic mutation.
It doesn’t particularly matter when the egg or sperm were made in the person’s life time. If the parent has a mutation that they were born with, it can be passed on.
DNA replication still has to happen to create those eggs, and any time DNA is replicated there’s an opportunity for mutations to sneak in. So you accumulate a lot of mutations in the rest of your body over your lifetime that you won’t pass down to your kids, but there were some mutations that snuck in while your eggs developed.
A fetus will have all of the eggs they will have in their lifetime by the tenth week in utero.
I don’t have any other info that wouldn’t be pure speculation regarding the rest of your question, just wanted to add that tidbit.
When the egg is fertilized, there is cross talk between the genes. Both parents genes are mixed up to a point. The bases change places. So the child is not exactly half mother half father.
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