What Makes Children Who Grow Up in the Same Family So Different, Apart From Their Genes

This is a neat question! There are ii main reasons you 2 do not expect alike. The first is that the two of yous didn't grow upwardly the aforementioned fashion. And the second is that even though you lot have the aforementioned parents, you don't have the same genes.

Different Environment

The way yous grew upwardly is what geneticists call your surround. It includes where yous abound up, what you consume, and what you lot do. It too includes what your mom did and ate while she was pregnant with you.

All of these things play a function in the way yous look. People are different in part because no 2 people abound up in the same environment. Not even twins are together all the fourth dimension!

One example of how your environment tin can affect the way you expect is in your top. At that place are certain periods in your life when what you practise plays a large part in your height. Two of these times are when you lot are first built-in and when you hit puberty.

If y'all do not eat well during these two times and then you lot will be shorter. Only if y'all eat well then you volition be taller. Extreme examples of this include neglected kids and kids in state of war zones. They tend to exist much shorter than average.

There are lots of other traits affected by the environs. Things similar personality, weight, and intelligence but to name a few. While the environs is important, getting different cistron versions from your parents is probably an even bigger reason for why you and your brother ended upwardly so different.

These siblings look unlike because of their different genes and environment.

Different Gene Versions

Your genes play a large role in making you who you are. The color of your pilus, the color of your optics, and the dimples on your cheeks are all controlled in part past your genes.

At first it might seem like kids from the same parents should await alike. After all, kids get their genes from the same parents.

But brothers and sisters don't wait exactly alike because everyone (including parents) actually has two copies of nigh of their genes. And these copies can be dissimilar.

Parents pass one of their two copies of each of their genes to their kids. Which re-create a kid gets is totally random. And this is a large reason why you lot don't wait like your brother.

This is all a bit abstract and then let'due south use a specific example to hopefully make it all clearer. Let's look at the dimples some people accept when they smile.

The gene that makes dimples comes in two forms (or alleles), D  and d . D  gives you dimples and d  means no dimples.*

Similar near all genes, yous have ii copies of the gene that can give you lot dimples. Information technology is obvious what happens if you lot have ii D  copies -- yous have dimples. And two d  copies clearly means no dimples.

DD and Dd give you dimples, just dd does not.*

But what about a D and a d re-create? And so you take dimples. In genetics speak, nosotros say that D is ascendant over d (or that d is recessive to D ).

OK so what does that accept to do with you and your brother? Allow'southward do an case with some parents to show why this matters.

Permit'southward say your dad has a D  and a d  copy. He has dimples simply might pass the d  (no dimple) re-create to you. He is a carrier  of no dimples.

Which copy he passes to you is random. Information technology's like flipping a quarter. Half of the fourth dimension you get heads and one-half of the time you get tails. So at that place is a 50% hazard you go D  and a fifty% take a chance you lot get d  from your dad.

Permit'south say your mom doesn't accept dimples. This means that both of her copies are d . Which means she can just pass a d  to you.

So combining one copy from your dad and one copy from your mom means you either have D  and d  ( Dd ) or d  and d  ( dd ).

What this means is that each of your parents' children has a 50-50 shot at dimples ( Dd ) and a fifty-50 shot at no dimples ( dd ). If you got d from dad and your brother got D , then your brother would have dimples and you wouldn't.

Having dimples or not is simply one instance of many ways in which you and your brother may be different. Every person has nigh 20,000 genes. And many of these genes come in different versions.

So for every cistron where your dad has ii different copies, then y'all and your brother accept a 50-fifty shot of getting a different version. Aforementioned thing with your mom.

Allow'due south say that your parents each had x,000 genes with unlike versions. The odds that yous and your blood brother would become the same versions of each gene is really, really small. It'due south the aforementioned as flipping a quarter and getting heads 10,000 times in a row!

* And information technology's actually even more complicated than I'm showing here! Dimples actuallyisn't determined by a unmarried cistron. That makes it fifty-fifty more than likely that y'all and your sibling might inherit different versions!

The odds aren't actually that low

A big assumption we fabricated in coming up with these odds is that genes are independent of each other. In other words, each gene is passed on without any other gene affecting it.

This would be true if each of our genes is physically separate from the others. Merely they're not. Your genes are strung together on chromosomes. We have xx,000 genes on just 23 pairs of chromosomes. That means each of the chromosomes has lots of genes.

Parents do not laissez passer genes to their kids -- they pass chromosomes. So if genes are next to each other on chromosomes, then they often get passed downwards together.

People have two copies of each chromosome. Only one is randomly chosen to exist passed to a child.

Permit's say that the gene for dimples is next to the gene for wet earwax. Moisture earwax comes in two versions Westward  and w . Imagine your dad has D  and W  on one chromosome and d and westward on the other chromosome.

So if you accept dimples, so most likely you lot'll have moisture earwax too. And if you don't accept dimples, you'll have dry earwax (at least in this made upward example).

In other words, if you lot get D , you are almost sure to become W . And if yous become d , you are almost certain to become west .

Brothers Can Be Really Different

Merely like how yous don't think you look like your blood brother there is a similar case that has even made the news.Twin boys were born in July 2008. I had lite skin color and the other had dark pare color!

How did this happen? First the twins are congenial. This means their genes are as like equally not-twin brothers. Second they have a white German begetter and a Blackness African mother. Children of like mixed-race parents usually accept a blended skin tone.

All the same examples such every bit these German twins happen from fourth dimension to time. This is because in that location are at least seven unlike genes that affect pare tone. It's all up to chance which combinations the two brothers got. And in this case they got two very unlike combinations!

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Source: https://genetics.thetech.org/ask/ask279