State the genotypic and phenotypic ratios of offspring born to a carrier mother and a thalassemic father.

Question

Thalassemia is an autosomal recessive disorder that causes anaemic conditions in an individual. A blood smear from a heterozygous individual shows blood cells that are small, pale and irregularly shaped along with normal RBCs.

(a) State the genotypic and phenotypic ratios of offspring born to a carrier mother and a thalassemic father.

(b) Does the allele for thalassemia exhibit codominance? Justify.

Answer 1

(a) Genotypic rate

• Normal 25
• Carrier 50
• Thalassemic 25

Phenotypic rate

• Normal 75
• Thalassemic 25

(b) No, the allele for thalassemia doesn't parade codominance.

Codominance is an inheritance in which both alleles are expressed inversely in the heterozygous existent. In the case of thalassemia, the heterozygous existent has both normal and thalassemic alleles, but only the normal alleles are expressed. The thalassemic alleles are silenced.

This is because the thalassemia allele is a sheepish allele. This means that it's only expressed when present on both clones of the chromosome. However, the normal allele will be expressed and the thalassemic allele will be silenced If the existent has one normal allele and one thalassemia allele.