Cystic Fibrosis is caused by an allel which is

One of your parents would have polydactyly if you had a chance of inheriting it

Both parents have to carry the cystic fibrosis allele for you to inherit the disease

You can carry an allele for polydactyly and not have the disease

If one parent had cystic fibrosis you would definitely get the disease

Someone who is heterozygous for polydactyly will have extra fingers or toes

Someone who is heterozygous for cystic fibrosis will be ill with the disease

If you have cystic fibrosis your genotype would be homozygous recessive

Somone who has the phenotype of extra fingers and toes can be heterozygous or homozygous dominant for the polydactyly allele