Describe blood associated gene disorders linked to sex chromosome and chromosome 16.

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Q. Describe blood associated gene disorders linked to sex chromosome and chromosome 16.

Karnataka PUCKarnataka II PUC Board 2026Subjective· 5mImportance★★★★★

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Haemophilia is an X-linked (sex-chromosome) recessive bleeding disorder in which a clotting factor is defective; alpha-thalassemia is an autosomal recessive disorder controlled by the two closely linked alpha-globin genes (HBA1 and HBA2) on chromosome 16, causing reduced alpha-globin synthesis.

The question asks for two blood-associated gene (Mendelian) disorders — one linked to the sex chromosome and one linked to chromosome 16.

1. Haemophilia (sex-chromosome-linked disorder):

A sex-linked (X-linked) recessive disease transmitted from an unaffected carrier female to some of her male progeny.
In an affected individual a protein involved in the clotting of blood (a clotting factor) is defective, so even a simple cut leads to non-stop bleeding.
A heterozygous carrier female can transmit the disease to sons; because a female becoming haemophilic requires a carrier mother and a haemophilic father (very rare), the disease is far more common in males. A well-known example is its transmission in the royal family of Queen Victoria.

2. Alpha-thalassemia (chromosome-16 disorder):

An autosome-linked (autosomal) recessive blood disorder.
It is caused by mutation or deletion of the alpha-globin genes. There are two closely linked alpha-globin genes, HBA1 and HBA2, situated on chromosome 16, so a normal individual carries four alpha-globin gene copies.
When one or more of these genes on chromosome 16 are lost or mutated, synthesis of the alpha-globin chain of haemoglobin is reduced. The severity increases with the number of genes affected, ranging from a silent carrier to severe anaemia. …

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2026Set ANNUAL1 mark
$Q. Write the name of that inheritable disorder in which rate of synthesis of any one chain (α and β) of globin responsible for the synthesis of haemoglobin is decreasing.$
›Reveal solutionSolution

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 …

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CBSE 2022Set ANNUAL1 mark
$Q. Name one autosomal genetic disease. OR Name the bacterium used in transformation experiment by Griffith.$
›Reveal solutionSolution

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 …

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CBSE 2019Set ANNUAL1 markMCQ
$Q. Match the following :$
(1) Huntington's chorea
(2) Sickle cell anemia
(3) Agammaglobulinemia
(4) Thalassemia
(i) Autosomal mutant allele
(ii) Homozygous recessive gene
(iii) Autosomal dominant gene
(iv) Recessive gene
(a) (1)-(i) (2)-(iv) (3)-(iii) (4)-(ii)
(b) (1)-(ii) (2)-(iv) (3)-(i) (4)-(iii)
(c) (1)-(iii) (2)-(i) (3)-(iv) (4)-(ii)
(d) (1)-(iii) (2)-(i) (3)-(ii) (4)-(iv)
›Reveal solutionSolution

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 …

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CBSE 2018Set ANNUAL1 markMCQ
$Q. Name the human disease due to autosomal dominant gene:$
(a) SCID
(b) Sickle cell anemia
(c) Huntington's Chorea
(d) Thalassemia
›Reveal solutionSolution

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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Q.Describe blood associated gene disorders linked to sex chromosome and chromosome 16.

Concept understanding — Mendelian Disorders

Q.Describe blood associated gene disorders linked to sex chromosome and chromosome 16.

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