The increased vigour, quality, size, growth, or other functions of the hybrid over their parents occurring from the cross between two genetically unlike organisms, is called hybrid vigour. This is also called heterosis, a term given by Shull in the year 1914. Plant and animal breeders exploit heterosis by mating two different purebred lines that have certain desirable traits. One of the aims of Hybridization is to take advantage and utilize the hybrid vigour.

The term apomixis has coined by Winkler (1908, 1934). He defined apomixis as the substitution for the sexual process which does not involve any nuclear fusion. Hence, in the case of apomixis, embryo formation takes place by the asexual method instead of normal production by means of fertilization. Agamospermy and vegetative reproduction are the two main categories of apomixis.