identical twins share 100 per cent of their genes , meaning that until now it has been impossible to tell which sibling a sample comes from .
identical twins start life with the same genes because they come from the same fertilised egg which divides into two embryos .
in 2013 , 22-year-old twins mohammed and aftab asghar were both charged with raping a 17-year-old woman in berkshire because the police were unsure which one dna evidence came from .
mohammed was eventually convicted by a jury at reading crown court .