Cross pollination between pea plants.
Cross between purple colored flowers and white colored flowers in a pea plant.
Mendel tried cross pollination between pea plants with different traits such as varied colors of flowers. Mendel observed that the flowers of each pea plant were either purple or white – and never an intermediate between the two colors. These different, discrete versions of the same gene are called "alleles".
Mendel conducted experiments on true–breeding plants only, with traits that are discrete (either–or type) which enabled him to discover the particulate nature of inheritance. For example, Mendel cross–pollinated two contrasting, true–breeding pea varieties – for example, purple–flowered plants and white–flowered plants - which is called hybridization.
The parents are referred to as the P generation (parental generation), and their hybrid offspring are the F1 generation (first filial generation). Self pollination of F1 hybrids produce an F2 generation (second filial generation). Mendel could discover the basic patterns of inheritance by analyzing F2 generation plants.
The F1 hybrids from a cross between purple–flowered and white–flowered pea plants had flowers just as purple as the purple–flowered parents. But, when F1 generation plants which have purple flowers self–pollinate, one fourth of the F2 generation plants had white flowers. Mendel called the purple color as a dominant trait and white flower as a recessive trait. Mendel observed the same pattern of inheritance in six other characters, each represented by two different traits. Mendel developed the laws of inheritance to explain the 3:1 inheritance pattern that he consistently observed among the F2 offspring in his pea experiments.