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Asked by jd1 to Claire, Liad, Ruth, Ryan, Mako on 21 Jun 2015. This question was also asked by Moo Moo, pm.
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Ryan Cheale answered on 21 Jun 2015:
Slight variations make you who you are, these genetic changes come from when you were in the womb.
The main bulk is the same or we wouldn’t be human but the characteristics of our size, hair colour etc are determined by the small variations in our DNA.
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Claire Bryer answered on 21 Jun 2015:
DNA changes do not initially occur in the womb, they happen before you are even a foetus. Our body has a special way of shuffling our DNA and this is called ‘meiosis’. Meiosis happens when our body creates egg cells (in girls) or sperm cells (in boys).
Our DNA is contained in chromosomes and we have 2 sets of these. Each pair lines up during meiosis and then they ‘cross-over’. It’s rather complicated to explain but basically the sequences get mixed up a bit, so we are all basically a mosaic of our grandparents! Each pair then splits up and an egg or sperm cell gets a copy of each chromosome.
As well as meiosis creating differences, we can also pick up something called ‘germ-line mutations’, which are chemical changes at a single letter of the DNA sequence. Mutations usually happen when enzymes make a mistake in copying the DNA. Mutations don’t have to be bad, they can be a good thing.
This shuffling and changing of the DNA is important, because if we were all exactly the same (e.g. blonde hair) and a disease came along that wiped out people with blonde hair, the human race would not survive. We need diversity to survive, and this is the main thought behind evolution.
However, your friend will still share 99.9% of their DNA sequence with you. There are about 3,000,000 differences between you and any one person, so that gives you an idea of how big the human genome is!
🙂
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