Probability : 27/64
Work Step by Step
Autosomal Recessive Inheritance - only the Homozygous is affected. - Heterozygous is carrier (usually asymptomatic ). - more than one member in the family is usually affected. - male & female have the same risk. Types of Marriage 1- parents : pp X pp. eggs : all p . sperm : all p. offspring : pp. Marriage of 2 affected ( pp ) result in 100% affected ( i.e. all the children will have Phenylketonuria ). 2- parents : pp X Pp. eggs : all p. sperm : 1/2 P, 1/2 p. offspring : 1/2 Pp, 1/2 pp. ( 50% affected & 50% carrier ). 3- parents: Pp X Pp. eggs : 1/2 P, 1/2 p. sperm : 1/2 P, 1/2 p. offspring : 1/4 PP, 1/2 Pp, 1/4 pp. ( 25% affected PP, 50% carriers Pp, 25% normal pp) - these are average figures because the actual number of affected children will depend on the size of the family if number affected is 0 ( non of the 3 children have the disorder ) Probability : 27/64.