Answer:
Part A: Both the parents must be the carrier of the diseases that is, Cc.
Part B: one out of four or 25 percent chances are there that their offspring would have cystic fibrosis.
As cystic fibrosis is an autosomal recessive disorder, the individual needs to carry two copies of the recessive allele that is, homozygous recessive (cc).
It is stated that neither of the parents has the disorder but their offspring show the phenotype, then both the parents must be the carrier of the disorder that is, both must heterozygous (Cc).
The offspring produces by this cross can have three types of genotypes CC, Cc, cc in 1:2:1.
Thus, only one out of four would show the disease.
