Question

The figure given below shows a family pedigree (family tree) to show the inheritance of cystic fibrosis. [3 MARKS]



(a) Is the allele for cystic fibrosis dominant or recessive?
(b) State with reasons the genotype of individuals 1, 2 and 4.
(c) What are the possible genotypes of individuals 3 and 5?

Answer 1

Each Part: 1 Mark

(a) The allele for cystic fibrosis is recessive.
(b) Individuals 1 and 2 are heterozygous, because they are normal but produced an affected child. Individual 4 is homozygous recessive, since the allele is recessive and the individual must have two copies of the allele to be affected.
(c) Individuals 3 and 5 are normal but the information presented is not sufficient to determine whether they are homozygous dominant or heterozygous.