The nuclear structure of every living cell. Every human cell has normally 46 chromosomes. These chromosomes are made up of genes that govern all of the body's functions, and are also responsible for all the physical characteristics of an individual. Human gametes (i.e. eggs and sperm) contain only 23 chromosomes. When unified during fertilization, the total number of 46 chromosomes is thus restored. Abnormalities of chromosomes can result in miscarriages or congenital abnormalities. Age affects the quality of chromosomes in an egg and that is why infertility and miscarriages are more common in older women. For instance, the incidence of Down's Syndrome increases when a woman gets older.