Read the passage given below and answer the questions that follow.
DNA fingerprinting involves identifying differences in some specific regions in DNA sequence called repetitive DNA, because in these sequences, a small stretch of DNA is repeated many times. These sequences normally do not code for any proteins, but they form a large portion of the human genome. These sequences show a high degree of polymorphism and form the basis of DNA fingerprinting. Polymorphism (variation at genetic level) arises due to mutations. New mutations may arise in an individual either in somatic cells or in the germ cells (cells that generate gametes in sexually reproducing organisms). If a germ cell mutation does not seriously impair the individual’s ability to have offspring who can transmit the mutation, it can spread to the other members of the population (through sexual reproduction). The technique of DNA fingerprinting was initially developed by Alec Jeffreys. He used a satellite DNA as probe that shows a very high degree of polymorphism. It was called Variable Number of Tandem Repeats (VNTR).
According to the passage, a new mutation can spread to the other members of a population through sexual reproduction when it:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → arises in germ cells and does not seriously impair the individual’s ability to have offspring who can transmit it
The passage states that “if a germ cell mutation does not seriously impair the individual’s ability to have offspring who can transmit the mutation, it can spread to the other members of the population (through sexual reproduction).” Two conditions are needed. The mutation must be in the germ cells, which make the gametes, and the individual must still be able to have offspring.
Option (1) arises in somatic cells and does not affect the appearance of the individual — Incorrect. Somatic cells are body cells; they do not form gametes. A mutation in them stays in that individual and is not passed to the offspring, whatever its effect on appearance.
Option (2) arises in germ cells and does not seriously impair the individual’s ability to have offspring who can transmit it — Correct. A germ cell mutation reaches the gametes. If the carrier can still have offspring who pass it on, the mutation moves from one generation to the next and spreads in the population.
Option (3) arises in somatic cells of an individual who has many offspring — Incorrect. The number of offspring does not matter here. A somatic mutation never enters the gametes, so none of the offspring receive it.
Option (4) arises in germ cells and seriously impairs the individual’s ability to have offspring — Incorrect. The mutation is in the right cells, but if the individual cannot have offspring, there is no one to carry it forward.