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 statements about thalassemia is incorrect?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → It is transmitted from parents to the offspring when either one of the partners is an unaffected carrier for the gene.
The passage states that thalassemia is “transmitted from parents to the offspring when both the partners are unaffected carrier for the gene (or heterozygous).” Thalassemia is autosomal recessive, so a child is affected only when it receives the faulty gene from both parents.
Option (1) The defect affects the synthesis of one of the globin chains (α or β) of haemoglobin. — Correct statement. The passage says the defect results in reduced synthesis of one of the globin chains (α and β chains), so this is not the answer.
Option (2) The defect could be due to either mutation or deletion. — Correct statement. The passage says the defect could be due to either mutation or deletion.
Option (3) It is transmitted from parents to the offspring when either one of the partners is an unaffected carrier for the gene. — Incorrect statement. The passage says both partners are unaffected carriers. If only one parent carries the recessive gene, a child can at most be a carrier and cannot get the disease.
Option (4) It causes the formation of abnormal haemoglobin molecules, resulting in anaemia. — Correct statement. The reduced globin synthesis leads to abnormal haemoglobin molecules and anaemia, which is characteristic of the disease.