Question

since it does not show up often in a pedigree, what kind of allele is assumed that cystic fibrosis is caused by? incomplete dominant a recessive allele pleitropic allele a dominant allele

Explanation:

Cystic fibrosis is a genetic disorder. Recessive alleles are expressed (show in the phenotype) only when an individual has two copies (homozygous recessive). In pedigrees, recessive traits appear less frequently because carriers (heterozygous with one recessive allele) don't show the trait. Dominant alleles are expressed with one copy, so they appear more often. Incomplete dominant shows a blend, and pleiotropic affects multiple traits, but frequency in pedigree relates to recessive's requirement for two alleles. So cystic fibrosis is caused by a recessive allele.

Answer:

a recessive allele