Principles of Genetics and Breeding

6.1.2.2. Polyploidy

Gain/multiplication of whole sets of chromosomes. The genomic formula for autopolyploids is BB BB; the genomic formula for allopolyploids is BB CC. These two types have different origins.

• Autopolyploidy originates when in a dividing cell, spindle formation fails to occur, daughter chromosomes fail to segregate and the nucleus is reconstituted with double the normal chromosome complement.
• Allopolyploidy arises as a consequence of hybridization between species which are sufficiently closely related to produce viable hybrids but whose genomes have diverged as a result of chromosome structural change and differentiation at the gene level. As a result of such changes the F₁ interspecific hybrid may be completely sterile.

1. Autopolyploidy	-	duplicated sets from the same species (triploid tilapia)
2. Allopolyploidy	-	individual containing sets of chromosomes originating from different species (Mrigal- common carp hybrid)