Correct option is C
Ans. 3. A and D
Let’s break down each statement again:
Statement A: They have inherited these genes from their ancestors and this remains even though they no longer have eyes.
Correct: This is a valid explanation. The eyeless cavefish have inherited the genes for eye development from their ancestors, and these genes remain in their genome despite the absence of eyes. This is because evolution doesn’t always eliminate unused traits if there’s no selective pressure to do so.
Statement B: In case of a possibility that they return to the surface environment, retention of vision would be advantageous, so evolution retains this trait.
Incorrect: While this explanation may sound logical, it is incorrect in the context of evolution. The cavefish are not retaining eye development genes because of the possibility of returning to the surface environment. Evolution doesn’t retain traits just in case they might be useful in the future. Traits are retained only if they provide some current selective advantage. Since cavefish are living in an environment where sight is not necessary, there's no current selective advantage for retaining the genes for eyes. This makes Statement B incorrect.
Statement C: Evolution can only lead to gain of a trait, not loss of a trait.
Incorrect: This is a false statement. Evolution can lead to both the gain and loss of traits. In the case of cavefish, the loss of eyesight is a result of evolution in response to the dark environment. Loss of traits is a common occurrence in evolution when those traits are no longer useful.
Statement D: These genes are retained because of the combined role of these genes with other sensory mechanisms.
Correct: This is a reasonable explanation. Even if the eye-related genes are not used for vision, they could be involved in other sensory mechanisms, such as the lateral line system in cavefish. This system helps fish detect vibrations in the water, and the genes responsible for eye development might also play a role in enhancing other sensory abilities, thus explaining why these genes are retained.
Information Booster:
Eyeless Cavefish: Cavefish have lost their eyesight due to living in dark caves, where vision is not advantageous. Despite this, the genes involved in eye development remain in their genome due to genetic inheritance. Evolutionary loss of traits is common when they are no longer useful in a specific environment.
Evolution of Traits: Evolution does not preserve traits just in case they might be useful in the future. Traits are retained or lost based on current selective pressures. In the case of cavefish, the loss of eyesight is an example of evolutionary simplification (losing unnecessary traits).
Role of Genes in Other Sensory Mechanisms: Even though the eye-related genes in cavefish are no longer required for vision, they may still be involved in enhancing other sensory systems, such as the lateral line system, which helps them sense vibrations in the water.
