A woman becomes pregnant when one of her eggs becomes fertilised by a sperm. This usually happens after sexual intercourse, which takes place when the penis is placed inside the vagina and the man has an orgasm and ejaculates sperm. The penis needs to be erect in order for this to happen.
This single cell then attaches itself to the lining of the uterus more or less nine days after fertilisation – and the cycle of life begins all over again. Inside this tiny cell is the baby's genetic coding for life. It is only in the last few decades that scientists have begun to understand how this genetic coding works and what role chromosomes and DNA play in everyone's lives.