How related am I to my siblings?

Chris Smith put this to biologist Sarah Madden...

Sarah - It’s a really interesting question. I think the short answer - it’s a little bit complicated as many things are in science. You are 50% related to your parents, you are 50% related to your children. When it comes to siblings it’s - if we’re being all scientific about it - it’s 50% on average. The reason that is is that when you inherit the DNA from your parents, each chromosome that you have from each parent, there’s a bit of scrambling. So if you comparing different siblings they could take different parts of that chromosome and so it’s possible for you to be taking the same parts or completely different parts. So that’s why is 50% on average.

But I think it’s kind of cool to remember that this is relatedness and not the genetic similarity. So that would be the different bases that make up your DNA because just two random humans are 99.5% the same in terms of the DNA sequence. So basically, you and your family are, if you’re going to estimate 100% the same, which sounds crazy. But I think it really shows evolution in the fact that if you take two random things like a banana and a human, they are 50% the same in terms of the DNA sequence. Obviously, this is not relatedness - we’re not saying we’re related to bananas but the DNA sequence.

Chris - So, the chemical recipe book in our cells is basically 50% of the genes that are running a banana cell are also being used in your cells to make your metabolism work as well?

Sarah - Yes, so the DNA. It’s crazy.

Chris - It is, isn’t it? Not that you’re related to a banana or anything.

Sarah - No. Especially after the quiz you may think I am.