Would you have more of the same DNA with your brothers and sister than your Mom and Dad?

Question

I was thinkg about it, you get 50% from you mom and 50% from your father right?So if you have the same mother and father they would have the same as you right?

Am I right of wrong, just wondering?

Answer 1

You are correct that you share exactly 50% of you DNA with your father, and 50% of your DNA with your mother.

But you can share as much as 100% of your DNA with a sibling (i.e. if you had an identical twin) or as little as 0%.

So you could share a lot more, or a lot less with a sibling than you do with your parents.

How can this happen?

First, remember that humans have 23 pairs of chromosomes ... call them 1a-1b, 2a-2b, 3a-3b ... 23a-23b.   When your dad makes sperm cells, a sperm cell could get all the (a) chromosomes, or all the (b) chromosomes, or any combination in between.   So if you got 1a, 2a, 3a ... and so on ... it is conceivable that your sibling got 1b, 2b, 3b ... and so on.   This sibling would have to be of the opposite s*x (i.e. if you got a Y chromosome then this sibling would have gotten an X chromosome from your dad).

Same on your mother's side.

So it is possible (although unlikely) that a sibling could end up with exactly 0% of the chromosomes that you got.

Does that make sense?

Answer 2

You only get half from eother one of your parents though.

That means you are only 50% related to either one.

Your siblings recieved half their DNA from each parent too.

In one aspect this makes you more closely related to your siblings than to either of your parents.

Answer 3

You're wrong. We all have 50% of the DNA in common with both parents, and we share on average 50% of the DNA with our siblings. This is because the 50% DNA that goes in each sperm or egg is totally random. Imagine the extreme cases:

All of your mother's maternal chromosomes and your father's maternal chromosomes were in the sperm and egg that made you

All of your mother's paternal chromosomes and your father's paternal chromosomes were in the sperm and egg that made your brother

You would look a lot like your grandmothers, your brother would look a lot like his grandfathers, and you would have no DNA in common. Or the opposite could happen, and you look just like twins. So, on average, 50%.

Answer 4

You might think that you are more closely related to your siblings than to your parents, but the relationship between full sibs is only 50% on average, same as for each parent.  This is due to independent assortment during meiosis (formation of eggs and sperm).