What is genetic diversity?

How is diversity created? In the process of inheritance, nucleotides (although not always whole genes) are shuffled and recombined to form new combinations that are different than the parents. Every individual is a unique combination of alleles from its parents (unless it has been clonally propagated from just one parent; see box on cloning).

In addition, other events can create new variation in the DNA sequences. Mutations are changes to one or more nucleotides in the DNA sequence. They are caused by mutagens such as radiation (including ultraviolet radiation from the sun) or chemicals, or simply by mistakes during DNA replication. Mutations in somatic cells (nonreproductive cells) can cause problems, such as cancer, in an organism but are not heritable. Mutations in reproductive cells (gametes) are inherited by the progeny. These changes in the DNA sequence can be beneficial, detrimental (more often), or neutral. If they are beneficial they are more likely to be passed on to new generations, creating new genetic variation in the population.

Genetic diversity is important because it helps maintain the health of a population, by including alleles that may be valuable in resisting diseases, pests and other stresses. Maintaining diversity gives the population a buffer against change, providing the flexibility to adapt. If the environment changes, a population that has a higher variability of alleles will be better able to evolve to adapt to the new environment. In extreme situations (e.g. drought, disease epidemics) diversity could even mean the survival of the population.

Unfortunately, the process of domestication tends to decrease the genetic diversity of selected crop species, due in part to the genetic bottleneck imposed when only a few plants are selected and propagated. In addition, consumers tend to prefer uniformity – think of the rows of perfectly round, red apples we see in the supermarket. In nature, this is not a healthy situation. If anything unusual happens, such as a disease or environmental condition (e.g., a drought), there might not be any plants in the population that carry genes for responding to this new threat.