Radiation-induced gynogenesis and androgenesis in fish.

TL;DR: This work reported here is an investigation of the possibility of producing homozygous clones of fish rapidly by gynogenesis—a special form of artificial parthenogenesis in which activation of the eggs is achieved by fertilisation with genetically inert spermatozoa.

Abstract: CURRENT ideas on fish farming have stimulated interest in fish genetics and highlighted the need for more genetic analysis, particularly of fish of commercial importance. A major difficulty in breeding fish of commercial interest is the long generation time of 3 years or more. The work reported here is an investigation of the possibility of producing homozygous clones of fish rapidly by gynogenesis—a special form of artificial parthenogenesis in which activation of the eggs is achieved by fertilisation with genetically inert spermatozoa. Gynogenesis was first observed in frogs by Hertwig (1911), who showed that a low frequency of apparently normal embryos appeared when eggs were fertilised by spermatozoa which had received radium gamma ray doses much higher than levels normally required to produce 100 per cent, abnormality. It was concluded that, at these very high doses, the genetic material of the spermatozoa was so thoroughly destroyed that it played no part in the subsequent parthenogenetic development of the egg. This \"Hertwig effect\" has been confirmed several times in amphibia (reviewed by Beatty, 1964), and, as in other forms of parthenogenesis in vertebrates, the resulting parthenogenomes are usually haploid, and although developing normally at first are grossly abnormal at hatching. However, sporadic occurrences of more normal hatchlings have been observed following parthenogenesis by pricking and these have been shown to be diploid (Parmenter, 1933; Kawamura, 1939). Several mechanisms have been proposed to explain the process of diploidisation (see Tyler, 1941; Beatty, 1964), but the experimental evidence in amphibia seems to favour diploidisation by doubling of the haploid female genome during cleavage. Thus Parmenter (1933) and Kawamura (1939) observed delayed cleavage in parthenogenetic eggs which subsequently produced diploid organisms, and Subtelny (1958) produced diploid individuals following transplantation of haploid nuclei into enucleated eggs, i.e. diploidisation in the absence of polar bodies. Increased frequencies of both haploid and diploid gynogenomes have been reported by Rostand (1934, 1936) following post-fertilisation cold treatments of amphibian eggs; gynogenesis was produced by irradiated spermatozoa and also by fertilisation of eggs with foreign spermatozoa (\" false hybrids \"). Gynogenesis is a natural form of reproduction in the teleost Mollienesia formosa (Hubbs and Hubbs, 1932), and the existence of distinct clones in laboratory fish has been demonstrated by tissue transplantation tests (Kallman, 1962). Perfectly normal and fully viable broods can easily be reared, and this suggests that diploidy is retained through suppression of meiosis Kaliman, bc. cit.) leading to fixed heterozygosity. Recent work in Russia (Romashov, Belyaeva, Golovinskaia and Pro-