Beta-thalassemia is an autosomal recessive mutation of HBB , the gene that makes

Question

Beta-thalassemia is an autosomal recessive mutation of HBB, the gene that makes the beta chains of hemoglobin. Symptoms are severe anemia and membrane damage of the erythrocytes. Beta-thalassemia is found among people of Mediteranian ancestry. A couple with beta-thalassemia in both their families have lost their first child to thalassemia. Now the wife is 15 weeks preg their second child and are asking for genetic counseling.

a) Given their family history, what are the genotypes of the husband and wife?

b) Therefore, what is the probability their second child will have beta-thalassemia?

c) What test(s) would you suggest to test for the genetics of fetus?

Explanation / Answer

a). Beta thalassemia is an autosomal recessive mutation. The parents are unaffected but they had an affected child means, they are heterozygous.

b). Assume that the gene coding for normal beta chain of haemoglobin is B and the gene coding for recessive phenotype is b; B is dominant over b.

Bb* Bb ----> B_ (3/4, normal phenotype), bb (1/4, beta thalassemia)

Thus, the probability of having beta thalassemia is = 25% (1/4)

c). Prenatal screening tests are used to detect genetic abnormalities in the fetus. They include amniocentesis and chorionic villus sampling.

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