The nucleus of a cell contains chromosomes. Each chromosome is made from one very long molecule of DNA, coiled up tightly so that it fits inside the tiny nucleus.
Each chromosome carries a large number of genes. A gene is a short section of DNA that holds the instructions for making a protein. Between them, the genes control how the cell and the whole organism develop.
In body cells the chromosomes are normally found in pairs. One chromosome in each pair came from the mother and the other came from the father. A human body cell has 23 pairs of chromosomes, which makes 46 in total, so 23 came from each parent.
