I) Plant breeding is the process by which humans change the characteristics of plants over time to make them better crops and more nourishing food.
In its most simple form, breeding consists of selecting the best plants in a given field, growing them to full seed and then using that seed to grow further generations.
Such selective breeding changes the genetic composition of the plants over time.
The most important factor for plant breeding is genetic variation in the desired characteristic.
For example, a farmer who wants to select a plant with resistance to an insect pest will watch for the plants that survive an insect attack. Another farmer wanting larger fruits will save seeds from plants yielding the biggest fruits in the field.
The most important factor for basic selective breeding is to start with plenty of genetic variation (top diagram) and to select and multiply the characteristic of interest (bottom diagram).
As a result from breeding, most of the species we rely on for food are very different from their wild relatives.
II) Animal Breeding
Breeding means, the manner in which selected males and females are mated. Breeding makes new combination or sequencing of genes in the individual.
The breeders identify and select desirable qualities in animals for future mating and discard less desirable qualities.
For the improvement of live stock (= farm animals) selection and breeding must be practised simultaneously.
Classification of Breeding Systems:Under the selected breeding system selected males and females are mated. The breeding system can be classified into five different ways depending on their phenotypic and genotypic relations.
The five breeding systems are:
(1) Random mating,
(2) Phenotypic assortive mating,
(3) Phenotypic dissortive mating,
(4) Genetic assortive mating and
(5) Genetic dissortive mating.