Eggs
A fertile young woman usually releases one egg a month, from one of her two ovaries. Unless the egg is fertilised within the next 24 hours, it dies. At its centre, the egg contains half the instructions (genes) needed to make a new person. The rest of the cell is a rich food store for the fertilised egg during the first few days of its life. A baby girl is born with around half a million eggs already formed in her undeveloped ovaries. However, only about 400 are released in her lifetime, between puberty and the menopause.
