Q.Both parents of a child are unaffected carriers (heterozygous) for beta-thalassemia. Using a Punnett square, work out the probability that their child will be born with the disease.

Thalassemia is the inherited blood disorder in which synthesis of one of the globin chains (α or β) of haemoglobin is reduced.

Thalassemia is an autosomal recessive quantitative disorder of haemoglobin synthesis — the mutation(s) reduce the rate of synthesis of either the alpha (α) or beta (β) globin polypeptide chain (unlike sickle-cell anaemia, which is a qualitative defect producing an abnormal globin). Depending on which chain is affected, it is classified as α-thalassemia (controlled by two closely linked genes, HBA1 and HBA2, on chromosome 16) or **β …

Sickle-cell anaemia is caused by a recessive allele on an autosome (chromosome 11), not a sex chromosome.

Sickle-cell anaemia is a well-known autosomal recessive genetic disorder caused by a point mutation in the gene coding for the beta-globin chain of haemoglobin (located on chromosome 11, an autosome, not a sex chromosome). Homozygous recessive individuals (HbSHbS) produce abnormal, sickle-shaped red blood cells, causi …

Huntington's chorea is autosomal dominant; sickle-cell anaemia stems from an autosomal mutant (beta-globin) allele; agammaglobulinemia follows a recessive-gene pattern; and thalassemia is expressed in the homozygous recessive state.

Huntington's chorea is caused by a dominant mutant allele on an autosome, so even one copy causes the disease (autosomal dominant). Sickle-cell anaemia is caused by a single point (missense) mutation in the beta-globin gene — described here as an 'autosomal mutant allele' — and the disease is fully expressed when the mutant allele is inherited from both parents. Agammaglobulinemia (an antibody-deficiency disorder) follows a recessive pattern. Thalassemia results from mutations affecting globin-chain synthesis and produces the major (severe) form specifically when …

Huntington's chorea is the autosomal dominant disorder.

Huntington's chorea is caused by a single dominant allele on chromosome 4 (an autosome); an affected person needs only one copy, and it typically appears in mid-adult life. This is a standard NCERT Class 12 Biology inheritance example and a frequent zoology previous year question.

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