Final answer:
The two major variants that introduce new genetic variation into a population are mutation and sexual reproduction, critical for the evolution and adaptability of species.
Step-by-step explanation:
The question 'Two major variants represented by _______and _________.' is extremely broad, but referencing Fig. 2a and 2b as well as mentioning the introduction of new genetic variation to a population, it can be inferred that the question is related to evolutionary biology, specifically the mechanisms that introduce genetic variation into a population.
Evolutionary processes such as mutation and sexual reproduction play critical roles in introducing genetic variability. Mutations are random changes in the DNA sequence, which can lead to new traits in organisms. Sexual reproduction, on the other hand, involves the combination of genetic material from two parents, creating offspring with a unique mix of genes. Both mutation and sexual reproduction contribute to the diverse array of characteristics observed within a population, as visualized in the frequency histograms of Fig. 2a and 2b. Understanding these processes is essential for comprehending how populations evolve over time and how species adapt to their environments.