(a) Mendel found that only tall pea plants were produced in the first generation when he crossed pure-bred tall pea plants with pure-bred dwarf pea plants (F1). The tall plants and dwarf plants were produced in the second generation, or (F2), in a ratio of 3:1. He then self-crossed the tall pea plants of the F1 generation. Mendel said that the dwarfness of one of the parent pea plants had not been lost, but rather had been suppressed or hidden in the first generation before resurfacing in the second. He characterized the expressed trait of tallness as the “dominant trait,” and the suppressed feature of dwarfism as a “recessive trait.”
Mendel’s work with tall and dwarf pea plants demonstrated this.
(b) Mendel observed two traits—round-yellow and wrinkled-green—combined in seeds, and two new traits—round-green and wrinkled-yellow—had formed in the F2 generation. More than one pair of traits are taken into account in a cross at once, and the factors causing each pair of traits are transmitted independently to the gametes, in accordance with Mendel’s second law of inheritance.
The cross shown below is a dihybrid cross and demonstrates how two traits can be inherited independently of one another.
