Question

How do variations arise in organisms? "Variation is useful for the survival of species." Justify this statement with the help of an example.

Answer 1

The variations in organisms can arise due to various reasons. Most common of these are the variations caused due to sexual reproduction and variations caused due to mutations.
In sexual reproduction, the gametes are formed by meiosis, during which crossing over of chromosomes occurs, giving opportunity for new combination of genes. Then, the fusion of these haploid gametes takes place, which further leads to combination of DNA belonging to two different organisms, and, thus, results in varition in the newly formed individual.
Some variations may also occur due to random mutations in the genome of an individual. If these mutations are beneficial, they may get inherited to the next generations also, and, thus, lead to variations.
Most of the times, variations developed, are helpful for the survival of species. The new variations, if associated with more chances of adaptations with changing environment, are selected by the nature and thus give better chances of survival to the species.
It can be understood with the help of following example:
A small population of red beetles live in a bushy area with green leaves. Crows can easily find and eat these beetles. Now, a colour variation arises during reproduction in these beetles, due to which the colour of one progeny beetle changes from red to green. The green beetle can now hide itself in leaves to escape from being eaten by crows. Thus, the variation provides a survival advantage to the beetle. Hence, the red beetles are rendered more vulnerable. Their chances of survival are lesser in comparison to green beetles. This leads to an increase in the population of green beetles.