Question

Which one of the following is caused by point mutation?

• A. Turner's syndrome
• B. Down's syndrome
• C. Sickle cell anemia
• D. Kleinefelter's syndrome

Hint:

Remember that Sickle cell anemia is a classic example of a genetic disorder caused by a single point mutation—just one base change can have a huge impact on protein function and phenotype.

Answer 1

The Correct Option is C

Step 1: Understand what a point mutation is.
A point mutation is a change in a single nucleotide base in the DNA sequence of a gene. This can result in the replacement of one amino acid with another during protein synthesis, potentially altering the structure and function of the resulting protein.
Step 2: Identify the disorder caused by point mutation.
Sickle cell anemia is caused by a specific point mutation in the gene that encodes the beta-globin chain of hemoglobin.
Step 3: Analyze the molecular change.
In sickle cell anemia, the codon GAG (which codes for glutamic acid) is mutated to GTG (which codes for valine) at the 6th position of the beta-globin gene. This single base substitution (A to T) results in the production of abnormal hemoglobin S instead of the normal hemoglobin A.
Step 4: Understand the effect of the mutation.
The replacement of hydrophilic glutamic acid with hydrophobic valine causes the hemoglobin molecules to stick together under low oxygen conditions, leading to the characteristic sickle shape of red blood cells. These cells are less flexible and can block capillaries, causing pain and organ damage.
Step 5: Eliminate the incorrect options.
Turner's syndrome (45, X) is due to monosomy of the X chromosome.
Down's syndrome (Trisomy 21) is caused by an extra copy of chromosome 21.
Klinefelter's syndrome (47, XXY) results from an extra X chromosome in males.
These are all chromosomal abnormalities, not point mutations.