An interesting question was asked: if half the chromosomes come from a person’s father and the other half from the mother, why aren’t siblings simply identical twins born at different times? In other words, what mechanism controls individuality?
Dr Phil Zegerman provided a nice answer (listen from 25:04):http://ec.libsyn.com/p/1/0/3/10347f3b4ced3abb/Naked_Genetics_12.08.14.mp3?d13a76d516d9dec20c3d276ce028ed5089ab1ce3dae902ea1d01cc8033d9ca54afd9&c_id=4824544
The transcript can be found here (‘Why are children all so different?’).
You can also watch this lovely animation of the process Dr Zegerman describes – meiosis:
And this is what it actually looks like in a fruitfly: