Topic 1 - Variation: Genetic Diagrams And Disorders

Question 1

Is the gene for sickle cell anaemia dominant or recessive? Explain your answer.

Answer 1

Recessive. The disorder can only be inherited of both parents carry the gene. A parent can be a carrier but not a sufferer.

Question 2

What is sickle cell anaemia? Describe its symptoms.

Answer 2

Sickle cell anaemia is a genetic disorder that causes red blood cells to be sickle-shaped. They get stuck in capillaries, which deprives the body of oxygen. Symptoms include tiredness, painful joints and muscles, fever and anaemia.

Question 3

Rachel and Harry are about to have a child. Both of them carry the cystic fibrosis gene but are not sufferers (both of their genotypes is Ff). What is the chance that their child will suffer from the condition? Explain your answer.

Answer 3

25%. As the cystic fibrosis gene is recessive, for the child to be a sufferer they will need two recessive alleles. There is a 1 in 4 chance of this happening: 
Possible outcomes:
FF - normal
Ff - carrier 
Ff - carrier 
ff - sufferer

Question 4

What are the symptoms of cystic fibrosis?

Answer 4

Symptoms include breathing difficulties, lung infections, malnutrition and fertility problems.