A gene is a set of instructions for making a particular protein. The instructions are ‘written’ in DNA, which is a very, very, very long molecule. If it was stretched out, the DNA in just ONE of your cells would be 3 metres long. There are about 100 trillion cells in your body (that is 100,000,000,000,000). All their DNA stretched out and laid end–to-end would reach right out of our solar system!
All of the DNA in one of your cells has the instructions for making a person (of course a frog’s DNA has the instructions for making a frog and a daffodil’s DNA has the instructions for making a daffodil).
All living things depend on genes!
Most DNA is kept in the nucleus of a cell, acting like a great big recipe book. Bits of it, like individual recipes, get copied out, and sent to the manufacturing parts of the cell, so that the cell can make the proteins it needs. This copying out is happening all the time because the cell uses lots of different proteins.
In our cells we have 2 copies of every gene; one from our father and one from our mother. Humans have about 35,000 different genes. There can be different versions of the same gene (like there are lots of different recipes for chocolate cake) these different version of the same gene are called alleles. You often get a different allele from your Mum and from your Dad.