Question: Why do some children look more like their mothers and others look more like their fathers?

Ravinder Kanda answered on 9 Mar 2015:

Interesting question! We can’t predict from DNA which of your mum’s features you will have or which of your dad’s. We can tell which bits of your DNA came from your mum and which bits came from your dad, but we can’t tell why you might inherit your mum’s nose, while your brother/sister might inherit your dad’s. Ultimately, these features are inherited in your DNA, but its all a bit of luck as to which of your parents features you will get.

Think of it this way: We are diploid organisms – that is we have 2 copies of each chromosome. Sperm and egg cells are haploid (there is only one copy of each chromosome present in them, and which copy, out of the 2 every individual has is present, is going to be random), so that when they combine to make a foetus, you get a diploid individual with the right number of chromosomes. You will have inherited one set of chromosomes from your mum and one set from your dad. But your brother/sister will have inherited a different combination of chromosomes from your mum and dad (depending on which copy of the chromosome was present in the sperm and egg cells that made them). For this reason, you and your brother/sister will look very different. Now clearly, this doesn’t apply to identical twins – they come from the same sperm and egg cell, so their DNA is identical, and so are their features.