Question

Define atavism with an example.

Answer 1

Hint:-The phenotypic and genotypic characteristics of all the animals are embedded in their DNA, which influences their growth and development. However, there is a claim that only less than 10% of the DNA is active while the rest is inactive.

Complete Answer:-Atavism is a phenomenon in which the phenotype of an organism resembles their ancestors even though it has been lost in evolution. This can also be taken as a proof of evolution. But why does it happen? The DNA has all the information needed for the body to function. Along with the necessary functional genes, it has genes that are inactive but are preserved in the DNA. These inactive genes hold the phenotypic features our ancestors had but are not expressed, as they are no longer useful for survival to the organism. However, when this gene gets suppressed accidentally, due to mutation, they get expressed. Some of the examples of atavism are humans born with vestigial tails, extra toes in modern horses, dewclaws in dogs, colour blindness in humans and teeth in chicken.

Note:- There is another phenomenon known as vestigiality, which is related to atavism but is completely different. In vestigiality, the organism retains the homologous ancestral body part, which has completely or partially lost its functionality through evolution. This happens when the body part does not influence the natural selection. The appendix in human, hind limbs of snake and whale are all vestigial structures. The presence or absence of these structures do not affect the organism.