Principles of Genetics and Breeding

8.1.4.2 Tetraploids

Induction of tetraploidy involves applying shock treatment soon after zygote formation (mitotic inhibition–doubled diploid). This is to prevent the first mitotic cleavage thereby inducing the tetraploid condition. Unlike triploids, tetraploids may reach sexual maturity.

• Tetraploids are induced in a similar way as triploids, but during a more advanced stage of embryonic development.

• A potential alternative to the problematic and expensive production of triploids by mechanical induction is the crossing of tetraploids with diploids.

• A tetraploid/diploid cross would be expected to produce all-triploid progeny that might be more viable than mechanically induced triploids, as triploid embryos would not have to undergo the same stress and damage that occurs during mechanical induction.

• Although tetraploid/diploid crossing remains a possible method for production of triploids, the optimal conditions to maximize tetraploid survival and growth rates need to be determined. Tetraploid fish and shellfish have only been sub viable and tend to grow more slowly than diploids.

• Except very few species (rainbow trout) tetraploids are mostly not viable beyond the fry stage. Tetraploids show poor viability, at least in the initial generation after induction and that it appears to be significantly more difficult to induce tetraploidy than it is to induce triploidy.