Thalassaemia and sickle-cell anaemia are both disorders of haemoglobin and both are autosomal…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Thalassaemia and sickle-cell anaemia are both disorders of haemoglobin and both are autosomal recessive. A student says that they are the same kind of problem.
- Explain how the two differ in what goes wrong with the globin.
- A carrier of each disorder is usually healthy. Why?
- A couple, one a carrier of thalassaemia and the other a carrier of sickle-cell anaemia, have a child. The genes are different. Is the child at risk of either disease?
Need a reminder? The key ideaShow
In an autosomal recessive disorder, two carriers (Aa × Aa) have children in the ratio 1 AA : 2 Aa : 1 aa. The chance of an affected child is , of a carrier , and each child is an independent event. Thalassaemia is a problem of the amount of globin, and sickle-cell anaemia is a problem of one amino acid of the globin.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) In thalassaemia the globin chain that is made is normal, but too little of it is made. This is a quantitative problem. In sickle-cell anaemia the chain is made in full amount, but one amino acid is wrong. This is a qualitative problem.
Step 2. (b) A carrier has one normal allele. It makes enough working globin for the body, so the person is healthy.
Step 3. (c) Each disease needs two copies of its own faulty allele. Only one parent carries the allele for thalassaemia, and only the other parent carries the allele for sickle-cell anaemia. So the child can get at most one copy of each faulty allele and cannot have either disease. The child may be a carrier of one of them, or of both.
Answer: (a) too little against a wrong amino acid; (b) one normal allele is enough; (c) no risk of either disease for the child, only of being a carrier.
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