Continued self-pollination results in 

Continued self-pollination results in inbreeding depression. This usually reduces fertility and even productivity.

(1) The progeny of crosses between different varieties of a plant species usually exhibits greater biomass
and fertility than either parent. This phenomenon, called heterosis or hybrid vigour, is capitalised to produce
superior yields for many crop species.

(3) Occurrence of more than one embryo in a seed is referred to as polyembryony.

(4) Variation in gene frequency that occurs by chance rather than natural selection is known as genetic drift.