Two structurally rearranged chromosomes are called reciprocal translocations when two chromosomes of different origins each break and rejoin each other in a transposition. Most of these translocations retain the original total number of genes and generally have no serious effect on gene action and individual development, so they are called balanced translocations. In meiosis, if two translocated chromosomes are together and two normal chromosomes are together in a germ cell, balanced gametes will be produced because such a separation ensures that each cell has a complete set of genes. If a translocated chromosome and a normal chromosome separate together and enter the germ cell, an unbalanced gamete will be produced. Balanced translocations are the most frequent type of chromosomal structural aberration in humans, with an incidence of about 1 in 500 to 1 in 1000 newborn infants.