The following pedigree shows inheritance of the recessive di

The following pedigree shows inheritance of the recessive disease PKU (phenylketonuria). The affected individuals I.1 and III. 1 have PKU. Individual III. 4 is pregnant with her first child, IV.1. (A) What must be the genotype of II.1 and II.2? (B) What must be the genotype of 1III.1? (C) What are the chances that III.3 is a carrier? (D) What are the chances that III. 4 is a carrier? (E) What are the chances that IV.1 will have PKU? Draw a pedigree pattern that shows a recessive trait that must be autosomal recessive (i.e. the pattern cannot be compatible with X-linkage). Do not draw more than 3 generations.

Solution

3. Let the \"P\" and \"p\" be the dominant and recessive allele of the trait.

A. Since both II.1 and II.2 are unaffected and one of their offspring are affected. So both II.1 and II.2 must be heterozygous. So their genotype is : \"Pp\"

B. Since III.1 is affected, so his genotype must be \"pp\".

C.

Genotype of II.1 - \"Pp\"

Genotype of II.2 - \"Pp\"

There are 2/3 that is 66.67% chances that III.3 is a carrier.

D.

Genotype of II.4 must be \"Pp\", as his mother was affected. Assuming II.3 to be homozygous dominant, The cross would be PP x Pp

There are 50% chances that, III.4 is a carrier.

	P	p
P	PP (normal)	Pp (carrier)
p	Pp (carrier)	pp