(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.
