How we receive DNA from our parents

People have long realised that children inherit physical traits from their parents, but it was not until relatively recently that we understood that heredity is due to DNA.

Most human cells hold a full copy of that person’s DNA. The exceptions are the sex cells – the male’s sperm and the female’s egg – each of which only contains half a set. The DNA is stored in thread-like structures called chromosomes.

During reproduction, the sex cells fuse together. The two half-sets of chromosomes, one from the mother and the other from the father, are thus combined to give the full set of genetic information needed to build another human being.

The new cell now divides and re-divides rapidly, forming a cluster of cells. This develops into an embryo, which develops into a foetus, and so on. As a cell divides, the DNA it contains is copied, so that each new cell receives a complete copy of the DNA present in the original.