It is due to failure of any of the process concerned with normal alteration of generation viz., development of pollen, embryo sac, and embryo endosperm causing non- functional gametes. So failure to set seeds, may be due to sterility, caused by non – functional gametes.
Sterility may be caused by chromosomal aberrations, gene action or cytoplasmic influences.
Sterility in auto polyplids, interspecific hybrids eneuploids and individuals carrying chromosomal aberrations in very often due to chromosomes
Sterility in autopolyploids.
Autopolyploids are usually highly sterile because the behaviour of chromosomes during meiosis in autopolyploids in peculiar due to the fact that they posses more than two homologous chromosomes
We shall consider meiosis in an auto triploid as an example of autopolyploids. During zygonema stage, genetically homologous regions of the chromosomes pair in such a very that at any one place, chromosome pairing in between two chromosomes only. Two of the three homologous chromosomes may completely pair as bivalent, leaving one chromosome unpaired as an univalent. There are seven possible configurations at diakinesis of an auto triploid as follows:
- Three univalents
- A ring bivalent and an univalent