Final answer:
Genetic diversity in a population comes from two main sources: mutation and sexual reproduction. Mutations can cause variation in appearance (phenotype) and environmental factors can also lead to variation in plants.
Step-by-step explanation:
Genetic diversity in a population comes from two main sources: mutation and sexual reproduction. Mutation, a change in DNA, is the ultimate source of new alleles or new genetic variation in any population. An individual that has a mutated gene might have a different trait than other individuals in the population. However, this is not always the case. A mutation can have one of three outcomes on the organisms' appearance (or phenotype).
Importantly, these differences must have some genetic basis; otherwise, selection will not lead to change in the next generation. This is critical because variation among individuals can be caused by non-genetic reasons, such as an individual being taller because of better nutrition rather than different genes.
Another cause of non-heritable variation in plants is environmental factors. Environmental factors such as temperature, sunlight, soil composition, and availability of water can lead to phenotypic variation in plants. For example, a plant growing in a shady area may produce larger leaves compared to a plant growing in a sunny area to maximize its light absorption.