Genes for some characteristics are stronger or more likely to appear in offspring than others. Each of the thousands of gene pairs in the body work as a team. Some gene pairs have two similar genes, while others have two different genes. An example is those who inherit genes for both A and B blood types. Since neither is dominant, they are AB blood types.
Geneticists now understand that only a few traits are controlled by a single gene pair.
Most are influenced by many genes. For instance, height depends on a dozen or more genes acting together. Normal variations in genes, known as polymorphisms , also impact on development. The Genetics of Growth and Development During periods of growth and development, existing cells divide many times to make new cells. However, before one cell divides into two, all the genetic information in the original cell is duplicated so it can be passed on to the new cell.