Science and Technology | Are siblings more closely related than they are to their parents?

I miss working as a Scientist, and especially in the field of DNA Analysis.  Last week I had a bit of science on my facebook feed that I quite liked and so thought I'd add it to my blog.   The question is asking about some pretty straightforward questions about the division of genes and just took a little bit of thought and a few seconds of discussion.


First of all, all your DNA comes from your parents, I think that is established, and so you are 50% related to each, and so with this recorded the investigation turns to how related to one another are siblings?  Well, meiosis is the key to this because this is the process that creates gametes, these are the reproductive cells that get together to produce the zygote, and it is the zygote that forms the children.  For the gametes to work they must have only half of each parents DNA, so when 2 come together to make the zygote we get back to one full set of DNA.

During meiosis the division into half sets of the parents DNA is random, as a result, on average all gemetes will share 50% of each others DNA.  This is an average and the distribution will be like a bell-shaped curve, and so in theory 2 zygotes might have no DNA that is the same, this is highly improbable, and I suspect never observed.  So, the answer is that will 50% of each zygotes DNA shared, and half from each, we are looking at half of 2 x 50% = 50%.