Genetics form the basis of the biological diversity we see around us. Genetic information, stored in DNA molecules in every cell of an organism, is transferred from one generation to another during sexual reproduction.
During fertilisation the DNA of the father (transferred via pollen or sperm) combines with that of the mother (transferred via an egg cell) to form a single cell embryo. This embryo then develops into a multi-cellular individual in which the whole set of genetic material is replicated in each and every cell. Cells use their copy of the genetic material selectively to establish their own characteristics and functions and in doing so differentiate into different organs to form a complete, genetically unique organism.
In this way every individual organism inherits a unique genetic “blueprint”, in the form of a unique set of DNA molecules, from its parents. Just like you need a specific set of information and instructions to build a particular vehicle, a specific, complete set of DNA molecules, called a genome or genotype, will yield a specific organism with particular characteristics.
Unique combinations of genetic material during fertilisation and changes (mutations etc.) in the DNA molecules over time result in genetic variation, which in turn, is expressed as variations in the visible traits, or phenotype, of organisms. This variability or genetic potential results in living organisms of the same species and even offspring from the same parents with distinct appearances and characteristics. Depending on the benefit a particular genetic trait may impart to the organism in a specific environment, it may be preferentially transferred to its offspring or may disappear completely over time.
By selecting individuals with desired traits and using them as parents, we can direct the genetic composition of their offspring to a certain extent and develop individuals/breeds/strains/cultivars with very particular characteristics - this is called breeding.
Breeding over many millennia has resulted in the development of crops with desirable traits that are very different from their original wild relatives.