Which of the following genetic disorder is not a type of Mendelian disorder?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Down's syndrome
Option (1) Colour blindness — A Mendelian disorder. Sex-linked recessive.
Option (2) Down's syndrome — Not a Mendelian disorder. It is a chromosomal disorder, caused by an extra chromosome 21.
Option (3) Haemophilia — A Mendelian disorder. Sex-linked recessive.
Option (4) Thalassaemia — A Mendelian disorder. Autosomal recessive.
Note: A similar question was also asked in CUET (UG) 2026 on 30-05-2026 (Slot 2) and on 14-05-2026 (Slot 1), and in CUET (UG) 2023 on 26-05-2023 (Slot 3).
NCERT Extract:
Chromosomal Disorders – “The chromosomal disorders on the other hand are caused due to absence or excess or abnormal arrangement of one or more chromosomes. Failure of segregation of chromatids during cell division cycle results in the gain or loss of a chromosome(s), called aneuploidy. For example, Down’s syndrome results in the gain of extra copy of chromosome 21.”
Mendelian 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.”