Mendel's Experiments on Pea Plant

Mendel's theory of inheritance - the particulate theory - proposed that heredity is carried by minute, discrete particles or factors (now called genes), rather than by any kind of fluid 'blending' between parents. To test this he ran controlled pollination experiments on several true-breeding (pure-breeding) lines of garden pea, lines that had been self-pollinated for many generations and so bred true for a given trait generation after generation, meaning they were homozygous for it. Garden pea allowed two kinds of matings: self-fertilisation, which happens naturally because a pea flower's own pollen and egg are contained together, and cross-fertilisation, which Mendel produced deliberately by emasculating a flower (removing its anthers before its own pollen matures) and then dusting its stigma with pollen taken from a different variety - a mating that produces hybrid offspring carrying traits from both parents. Mendel selected seven pairs of clearly contrasting, single-gene traits for study - stem length (tall/dwarf), pod shape (inflated/constricted), seed shape (round/wrinkled), seed/cotyledon colour (yellow/green), flower colour (purple/white), flower position (axial/terminal) and pod colour (green/yellow) - each with a well-established classical gene symbol (Le, R, I, A, Gp, V and Fa respectively). Later molecular work has traced two of these classical genes directly to real DNA differences: the tall/dwarf gene (Le) encodes an enzyme in the gibbere …