Read the passage and answer the following questions:
Genetic disorders may be grouped into two categories – Mendelian disorders and Chromosomal disorders. Mendelian disorders are mainly determined by alteration or mutation in the single gene. These disorders are transmitted to the offspring on the same lines as we have studied in the principle of inheritance. The pattern of inheritance of such Mendelian disorders can be traced in a family by the pedigree analysis. Most common and prevalent Mendelian disorders are Haemophilia, Cystic fibrosis, Sicklecell anaemia, Colour blindness, Phenylketonuria, Thalassemia, etc. It is important to mention here that such Mendelian disorders may be dominant or recessive. Thalassemia : This is also an autosome-linked recessive blood disease transmitted from parents to the offspring when both the partners are unaffected carrier for the gene (or heterozygous). The defect could be due to either mutation or deletion which ultimately results in reduced rate of synthesis of one of the globin chains (α and β chains) that make up haemoglobin.
Which of the following is an autosome-linked disease?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Both (1) and (3).
A disease is autosome-linked when its gene lies on one of the autosomes (the 22 pairs that are the same in males and females) and not on a sex chromosome. Both sickle-cell anaemia and thalassemia are autosome-linked recessive Mendelian disorders. The passage gives this only for thalassemia; for sickle-cell anaemia it comes from NCERT.
Option (1) Sickle-cell anaemia. — Correct statement, but it is only one of the correct points, so on its own it is not the answer. Sickle-cell anaemia is an autosome-linked recessive trait, controlled by the alleles HbA and HbS.
Option (2) Klinefelter’s Syndrome. — Incorrect. Klinefelter’s syndrome is a chromosomal disorder, not a single-gene disease. It is caused by an additional copy of the X chromosome, giving the karyotype 47, XXY.
Option (3) Thalassemia. — Correct statement, but it is only one of the correct points, so on its own it is not the answer. Thalassemia is an autosome-linked recessive blood disease, transmitted when both partners are unaffected carriers.
NCERT Extract:
Mendelian Disorders – “… Sickle-cell anaemia : This is an autosome linked recessive trait that can be transmitted from parents to the offspring when both the partners are carrier for the gene (or heterozygous). The disease is controlled by a single pair of allele, HbA and HbS.”
Mendelian Disorders – “… Thalassemia : This is also an autosome-linked recessive blood disease transmitted from parents to the offspring when both the partners are unaffected carrier for the gene (or heterozygous).”
Chromosomal Disorders – “… Klinefelter’s Syndrome : This genetic disorder is also caused due to the presence of an additional copy of X-chromosome resulting into a karyotype of 47, XXY.”