A couple went to see a genetic counselor because one of them has a sibling with cystic fibrosis. Cystic fibrosis is caused by homozygosity for a rare recessive and autosomal disease allele. Neither member of the couple nor any of their four parents is affected. What is the probability that their child will be a carrier of the cystic fibrosis disease allele (CF* CF)? Multiple Choice O 1/4 1/18 1/6 1/8 1/3 4/9