1. A. According to the map, which continents have the highest rates of cystic fibrosis? B. Based on the information from the reading, explain why this is the case.

2. What causes cystic fibrosis?

3. Typically, a lethal genetic disorder is very rare. Cystic fibrosis, on the other hand, is the most common potentially lethal genetic disorder among Caucasians. Describe one hypothesis explaining why this is the case.

4. Fill in the Punnett square below to visualize the offspring of a cystic fibrosis carrier and a person who doesn't have cystic fibrosis and isn't a carrier. Use F to denote the normal allele and f to denote the mutated CFR allele.

A. What percentage of their children are likely to have cystic fibrosis?

B. What percentage of their children are likely to be carriers of cystic fibrosis?

5. Fill in the Punnett square below to visualize the offspring of two cystic fibrosis carriers. Use F to denote the normal allele and f to denote the mutated CFR allele.

A. What percentage of their children are likely to have cystic fibrosis?

B. What percentage of their children are likely to be carriers of cystic fibrosis?

ANSWER IS:

1a. The highest rates of cystic fibrosis are seen in Europe, North America, and Australia.
b. This is because Caucasians of European descent have a higher frequency of the mutated allele that causes cystic fibrosis.
2. Cystic fibrosis is a recessive genetic disorder. An ion channel doesn't function properly, causing cystic fibrosis patients to have thick, sticky mucus. This causes respiratory infections and problems with digestive enzymes reaching the digestive tract, among other health issues.
3. Cystic fibrosis carriers are better protected against cholera and other gastrointestinal diseases, so over time, cholera epidemics have selected for cystic fibrosis carriers. These carriers lived long enough to pass their mutated gene along to future generations.
4. The cystic fibrosis carrier has genotype Ff and the person without the disease has genotype FF.
a. None of their children would have cystic fibrosis (0%). This is because none of the genotypes in the square are ff.
b. Half of their children would be carriers of the disease (50%). Carrier means they have the genotype Ff.
F F
F FF FF
f Ff Ff
5. A cystic fibrosis carrier has genotype Ff.
About one-quarter of their children would be unaffected by cystic fibrosis (25%). The unaffected genotype is FF.
F f
F FF Ff
f Ff ff