Everywhere on the internet, they say that eggs cause increased genetic malfunctions in babies as women get older, but if women were born with all their eggs (so all the genetic material is already made), why does it matter if she releases it at 20 years old or 40 years old?
I’m so confused, please somebody explain it to me like I’m 5.
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Because you accumulate DNA damage over time just through living. Since you’re constantly replacing most of the cells in your body, it isn’t that big a deal for them – but if you aren’t replacing them and they get damaged, that damage is there forever (sort of – there ARE dna repair pathways that are used to repair damage to cells that aren’t replaced frequently, but these are different to the pathways that can check for errors when a cell is copied)
This is also true of men, though (and studies seem to suggest the fathers age contributes MORE mutations to offspring) – because you can accumulate damage to the template you’re copying from, and also as you age your ability to repair DNA damage decreases generally.
It gets a lot more complicated if you really want to dive into WHY there are differences in maternal and paternal age contributing to mutations in children, down to how prone to mutation specific genes are
To put it simply, because they’re alive.
Like anything living, they deteriorate over time. The rest of the cells in your body are replaced once they deteriorate enough, but a woman’s eggs are not. All the damage they accumulate just remains until they die off. Of course, if one gets fertilised before it dies off, but after it’s severely deteriorated, then it can cause issues with the baby.
The damage can be caused by all number of thing such hormone exposure, natural radiation, toxins in the blood, physical trauma etc.
Two things:
One, women are born with all the follicles, which hold oocytes (eggs) as they mature and develop, and release them during ovulation. Since the eggs are still in there, they’re susceptible to anything that can harm the cells just like the rest of your body.
Two, while we don’t know how common it is, women can develop new eggs later on. This has been seen especially in those who undergo certain cancer treatments who should be sterile from it, but after a while they develop new eggs and become fertile again.
All of our cells are constantly exposed to DNA damage, like by radiation from space. Healthy cells can repair their damage, or the cells–like skin cells–simply die off and are replaced. Women are born with all of their eggs, and so the longer a woman lives, the more DNA damage her cells receive. These eggs can repair their DNA damage but their capability degrades over time.
By contrast, male sperm cells are generated every few months, and so there’s less accumulation of DNA damage.
Let’s say you build a block tower outside. Is it more likely to be standing (the same blocks in the same order you left it) after 20 years or after 40 years? There are more ways for random changes to make things wrong than correct so that is the more common direction for things to go. Our bodies have systems to keep the block towers mostly right and as a species this system is good enough so that some of our block towers persist but individually, sometimes our block towers fall over.
Ok I’m actually gonna explain like you’re 5 because this one is easy:
Let’s get some chicken eggs. I’m going to crack open one and cook and eat it right away. Want some? Yum!
Let’s leave another egg in the fridge for 2 months (age). Still so eager to eat it?
Let’s drill a small hole into another one and let air and other pollutants into it (substance abuse). Oh look, it’s growing mould. Want to eat it?
As we grow older so do our eggs. While we may not socially and culturally be ready to raise a person, the ideal biological age for a modern female human to reproduce is around 15-25. As in, once periods have become regular and before she’s stopped fully ageing.
But if we leave the egg in the fridge for a few weeks (mid 30s) it’s ok to eat them, they just might not be as fresh, but still fine to eat.
While women are born with their eggs, these eggs are not in full baby-making form yet. At the onset of puberty and again on fertilization, they go through more cycles of DNA division, which is susceptible to error.
This is in addition to background DNA damage.
Additionally, once the egg is fertilized, the cells rapidly divide, and each division is an opportunity for genetic damage.
Egg and sperm cells do not heal after they get damaged. Men make new sperm, but women don’t make new eggs. Cells can get damaged by certain foods, chemicals around us, radiation, sunlight and lots of other things.
The eggs will get hurt a little bit every now and then, that damage wont go away and the eggs will get more damaged as a woman experiences more of the things that cause damage throughout her life.
The DNA inside the egg can get damaged too, DNA is like instructions for cells on how to split and make more cells, but if those instructions are damage the cell might read the instructions wrong or be unable to do anything with those instructions.
ELI5. Every thing that is is changing into something else. A minimum of two different chemicals in contact and over time something changes.
So there’s a few answers. Most people are hitting on the most common: still accumulating mutations to existing follicles. The follicle still gets exposed to all the grossness of life.
BUT follicles aren’t finished! They actually divide again after the sperm starts it’s work on the cell. There’s a division that happens then and as people age the dividing process tends to go wonky. That’s why there’s so much higher risk of trisomy 21 (Down syndrome) as people get older: the chromosomes didn’t separate properly at this point.
All the things that we think of as causing cancer tend to make the division process wonky, especially as we get older. Since the follicle still has to divide after fertilization, if the machinery for the division is broken, problems happen. Even though the “egg” has been there since birth.
Stuff in the environment can alter the DNA in the eggs and cause mutations. Radiation, chemicals, stuff that the woman eats. Its the same reason that people get cancer – cancer is generally a specific kind of DNA mutation that disables or alters genes that control the rate cells divide and reproduce at. You aren’t born with cancer, but one sell gets mutated in this way and it (and its descendants) start dividing at an abnormally fast rate.
There is a massive scientific study going on in India where they are measuring the differences between women that are offered regular nutritional diet improvements and women that are not and they are then measuring the difference in genetic diversity between the eggs of their children. It’s been going on for years.
humans actually aren’t born with all their eggs. they are born with cells called oocytes which undergo meiosis, a type of cell division that produces eggs. in humans, one oocyte undergoes meiosis for each menstrual cycle. as a person ages, it becomes more likely that something will go wrong during this division and the chromosomes will be divided up incorrectly. this causes egg cells to have the wrong number of chromosomes, which can cause down syndrome or other syndromes. depending on which chromosome is affected, it often causes miscarriage.
Aside from the answers you have already received, the eggs aren’t “done” yet.
Normal cell division is mitosis. Eggs are created from meiosis.
In mitosis, the cell makes a copy of the DNA, and then it separates into two cells, each with one full copy of the DNA.
In meiosis, the cell makes a copy of the DNA, and then it separates into two cells, each with one full copy of the DNA. Then each pair separates into two cells, resulting in 4 cells, each with one half copy of the DNA.
In humans, only one of the 4 copies becomes an egg. The other 3 are not used.
The eggs are not fully formed at birth. They’re stuck between the first and second meiosis split until that particular egg develops into the one that will be released that cycle.
To answer your question, there’s two ways this leads to DNA damage
First, the DNA in that not-quite-egg-yet can get damaged just like any other cell’s DNA. Point gamma rays at it and it’s not going to be good for the DNA.
Also, the DNA can fail to separate properly in that second meiosis split, leading to situations where the baby is missing some or all of a chromosome, or the baby has some or all of a chromosome extra. This becomes more likely as the woman gets older. It’s assumed this is because the not-quite-eggs-yet have been on-hold for longer.
It degrades over time. That’s why older pregnant people have more complications.
Right. As eggs tends to get pretty expensive, and because it may worsen, you should buy and store 40 years worth of them.
Edit: in hindsight, that’s a pretty stupid, non working analogy.
Wont delete to teach me a lesson
Eggs degrade over time. Imagine buying a dozen eggs and putting them in your refrigerator. Would you expect the cake you made with some of those eggs six months later to be as good as the one you made with some the first week?
We have all our (what will be) eggs, but they’re not fully cooked. Up until it’s ready to be released, changes can and do happen.
Put a dozen eggs in your fridge.
Eat one a year.
Is the 12 year old egg as fresh and tasty as the 1st egg you ate?
Before a female fetus is born, all her eggs go through the process of meiosis. The thing is, meiosis actually has a stage I and stage II. The chromosomes separate once during meiosis I, but before separating again, the oocytes go into an arrested development until 15-40 years later, when they’re fertilized. Then they finish meiosis. The spindle fibers attach to the sister chromatids and separate them.
This is the real problem with trisomy cases. With time, the fibers become weaker, and don’t separate the chromosomes. So now you have an egg with an extra chromosome, and a polar body with a missing chromosome.
There are likely other specific reasons that cause other genetic malfunctions, but “nondisjunction” is usually the most concerning (as explained above). But I don’t think it has to do with the genes going wrong specifically, it’s the process of completing meiosis that is likely to fail.