This refers to diversity in gene frequencies. Genetic variation can lead to different traits within individuals of the same species, much like how different books have unique stories even though they all use the same alphabet.
Mutagen: A mutagen is an agent, such as radiation or a chemical substance, that causes genetic mutation. It's like someone randomly changing letters in our book without us knowing it.
The genotype is the part of the genetic makeup of a cell, which determines specific characteristics (phenotypic) of that cell/organism. It's like having an original manuscript for our book - it contains all information needed to create and understand it.