S4.2.6 For the adult
Family trees and genetic disorders
Two healthy parents have a child with cystic fibrosis. How can that happen?
What this chapter teaches
Cystic fibrosis and sickle cell disease are inherited in a recessive way. Two copies of the allele cause the disease, and one copy makes a carrier who is usually healthy. Two carriers have a 1 in 4 chance of an affected child each time. Carriers of the sickle allele have some protection from severe malaria.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why can two healthy parents have a child with a recessive disorder?
- What is the chance that a child of two carriers is also a carrier?
- Why is the sickle cell allele common in places where malaria is common?
After the chapter, the learner can
- Read a family tree to find who carries an allele
- Explain how sickle cell disease and cystic fibrosis are inherited
What they copy into their notebook
Carriers have one copy of a recessive allele and are usually healthy. Two carriers: 1 in 4 affected, 1 in 2 carriers, 1 in 4 not carriers. Squares are males, circles are females.