CF is an autosomal recessive disorder that varies widely in phenotype, from great difficulty in breathing and digesting, to frequent bouts of sinusitis, bronchitis, and/or pneumonia. In the Maxwell family, the mother, Matilda, has a mild case—she often suffers from respiratory infections. Her husband Jake is a heterozygote, and testing reveals that he carries an allele associated with severe disease. Of the four Maxwell children, Katie and Jim are severely affected, although Jim has to be hospitalized more frequently than Katie. The other two children, Emily and Rose, do not have CF. Explain how Katie and Jim can have severe cases of CF when one parent does not have the disease and the other has a mild case. Explain how Katie and Jim have different severities of the illness. What is the probability that Emily or Rose is a carrier, like their father?