Respuesta :
25% since there's a 25% chance they'd be homozygous dominant(not have CF) and a 50% chance they'd be heterozygous dominant(not have CF) then the last 25% is the potential they'd be homozygous recessive(have CF)
The right answer is 25%.
Here are the different cross between the gametes of parents:
A: healthy allele
a: sick allele.
Aa x Aa
AA, Aa, Aa, aa
Since cystic fibrosis is an autosomal recessive disease (chromosome 7): The disease is expressed only in children with two sick alleles (aa) (which represents one in four children). Those with only one sick allele (Aa) will carry the disease.