Since they are from the same parents can siblings or especially have the same DNA. its the same set of 50% genes right? What makes them different if there are not the same since the prerequisites are identical.
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Twins and siblings are like drawings made with the same set of crayons. Identical twins have drawings that look almost identical because they use nearly the same DNA “colors,” while fraternal twins and siblings have more variations in their drawings. So, identical twins have almost the same DNA, but not perfectly so, and other siblings share a lot but with more differences between them.
Nature vs nurture would be one huge aspect.
You yourself would be a totally different person if you grew up Amish or were adopted oversees by a Japanese couple.
Fund fact: Their fingerprints are still different as that’s due to the swirling/movements of the amniotic fluid in the uterus. Their irises are also different. So FaceID would work but not TouchID.
While siblings share a lot of DNA the near random nature of combining the parents DNA means that they will all be unique.
Each parents DNA is split into 2 pairs of chromosomes and the chances of a child getting any particular combination of those is 1/4.
Even if two children share the same pair of chromosomes there will be a lot of genetic differences depending on which genes they get or become active during the development process.
It is at least theoretically possible for two children to be genetically identical, but the chances of that happening are basically non-existent.
The exception is identical twins. In most instances identical twins have nearly identical DNA. This is because identical twins come from the same fertilized egg that split two very early in development. But changes that occur during the early development process will cause small changes to their respective DNA, so they aren’t going to be exactly identical.
If two sets of identical twins marry, there respective children from a genetic standpoint will be siblings because they all share the same source DNA. But again due to the nearly random nature of how they combine the will likely all be unique.
Let’s set aside identical twins for a second, because they are not created by different egg and sperm cells, but in fact split early in the development process after fertilization.
They could, theoretically (we’ll ignoring mutation). But the odds of that happening are so incredibly low that in practice it’s never going to happen.
A person’s genes contain 46 genes in 23 pairs. When the egg and sperm is created (through meiosis) those pairs are split so one of the pair goes in one cell the other pair goes in another. So possible number of different egg/sperm cells you can make is 2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2=8,388,608.
But that is only from one parent. The egg and sperm are separate so for each possible gene combination in the egg you have all those possible combinations for the sperm as well.So the total number of chromosome combinations for a child is 8,388,608*8,388,608=70,000,000,000,000. That is 70,000 BILLION posibilities, all of which are equally likely.
Now for identical twins, they will still have the same chromosome combinations, but there will likely be a small number of generic differences due to random mutations that happen when each is only a small number of cells.
>its the same set of 50% genes right? What makes them different if there are not the same since the prerequisites are identical.
Imagine you have 20,000 coins, and you’re going to flip them all. You’ll very likely get something very close to 50% heads and 50% tails… but every time you flip the set of 20,000, you will not get the same outcome of heads or tails *on the same coins*; The first time you flip them all, coin 205 might come up heads, but it might come up tails the next time.
Identical twins have the exact same coin flip results throughout the set (rather, you just did a single set of flips, and gave the results to both of them). Other siblings including fraternal twins are the result of separate coin flip sets, so even if you are starting with those same 20,000 coins, they will turn out differently, and it’s incredibly unlikely that you manage to copy an earlier set of flips just by chance.
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