Question

A point mutation is?
A. Sickle cell anemia
B. Thalassemia
C. Night blindness
D. Down’s syndrome

Answer 1

Mutation is any sudden change in the genetic material of an organism. It is of various types- genomic mutation, chromosomal mutation, and gene mutations. The mutation occurring in a single gene is called point mutation.

Complete answer:
Sickle cell anemia
Sickle cell anemia is an autosomal linked recessive disorder which is controlled by a single pair of the allele. The defect is caused as at the sixth position of the beta chain of haemoglobin, the substitution of glutamic acid by valine occurs.
The mutant haemoglobin molecule undergoes polymerization under low oxygen tension that causes change in the shape of RBC from biconcave disc to elongated sickle cell and hence the name sickle cell anemia. These deformed cells prevent the development of Plasmodium in the body so sickle cell anemia helps in preventing malaria.
Thalassemia
Thalassemia is a group of genetic disorders which result from the defective synthesis of subunits of haemoglobin. It is of two types: alpha-thalassemia and beta-thalassemia.
Night blindness
It is also called nyctalopia and it is the inability of a person to see well at night. The other symptoms of this disorder are scotoma and blurred vision. It mainly occurs due to deficiency of vitamin- A.
Down’s syndrome
Down syndrome, also known as Mangolian Idiocy, occurs due to trisomy of the 21st chromosome. Rounded face, broad fore-head, small ears, flattened nasal bridge, open mouth, protecting lower lip, skin fold at ear corners, protruding tongue, short neck, small flat hands with stubby little finger, loose jointedness at ankles, mental retardation, underdeveloped gonads and genitals are the characteristic features of this syndrome.
So, the correct answer is “Option A”.

Note: Mendelian disorders occur due to alteration or mutation in a single gene. These are inheritable disorders i.e. these are inherited by offsprings from their parents. For example, haemophilia, sickle cell anemia, etc.