The individual sexually reproducing organism—including humans—begins life as a fertilized egg, or zygote. Trillions of cell divisions subsequently occur in a controlled manner to produce a complex, multicellular human. In other words, that original single cell was the ancestor of every other cell in the body. Once a human individual is fully grown, cell reproduction is still necessary to repair or regenerate tissues. For example, new blood and skin cells are constantly being produced. The type of cell division associated with these events is mitosis , which produces genetically-identical cells with two sets of chromosomes (i.e. diploid). However, Humans also have to be able to produce specialized cells for reproduction (i.e. gametes) that contain only one set of chromosomes (i.e. haploid). The type of cell division associated with gamete production is meiosis .