Family trees showing AR inheritance. If both parents are carriers, there is a 25% risk of an affected child in any pregnancy, independent of gender. The diagram on the right illustrates a consanguineous relationship between first cousins (

see Consanguinity, p. 12). A common ancestor is a carrier for a recessive mutation that may occur in homozygous form in a descendent as a consequence of consanguinity. (Reproduced from Firth, Hurst and Hall (2005). Oxford Desk Reference—Clinical Genetics, with permission from Oxford University Press.)

See Fig. 2.4, p. 42.