Mendel's observation on hybridization in Pisum
Mendel took as his parental lines
(P)
two pure-breeding lines of garden peas
(Pisum sativum) that differed
in a single
character (coat colour), which
existed in one or the other of two phenotypes
(yellow or green). When the two
lines were artificially crossed, the offspring were invariably yellow.
When these first filial generation
(F1) plants were crossed, seeds of both
colours were observed in the F2 generation. Mendel's scientific insight
was to count
the relative proportions of the two phenotypes: he found that they always occurred in a 3:1 ratio, with the F1 phenotype predominating.