Induction of Allotriploids and Allopentaploids in Interfarnilial Hybrids, Female Spinous Loach x Male Carp and Female Loach x Male Carp

ドジョウ料とコイ科間の交雑である二倍体シマドジョウ雌×コイ(ニシキゴイ)雄および二倍体ドジョウ雌×コイ(ニシキゴイ)雄より生じる仔魚は奇形を呈し致死的であった。ニシキゴイの核型は微小染色体と不対の染色体を含み、染色体数も一定でなかったが、核型が本研究および既往の報告の範囲にあるとすると、上述の雑種はいずれも両親種の中問的な染色体構成を示した。科間交雑後の低温あるいは圧力処理による第二極体放出阻止の操作により、異質三倍体が得られた。四倍体のシマドジョウあるいは四倍体のドジョウとコイ雄との交雑からは異質三倍体が生じ、交雑直後の第二極体放出阻止により異質五倍体が得られた。以上の異質倍数化により雑種仔魚の奇形の程度は緩和される傾向が見られたが、生存性個体の作出には到らなかった。Interfamilial hybridizations between female diploid spinous loach (Cobitis biwae, 2n=48) and male carp (nishikigoi, colored—carp, Cyprinus carpio) and those between diploid loach (Misgurnus anguillicaudatus, 2n=50) and male carp gave rise to inviable larval development with the expression of external abnormalities. In the colored-carp, chromosome number was about 100 and karyotype included micro chromosome and unpaired chromosome. Chromosomal observation on the interfamilial hybrids showed that they had intermediate karyotypes comprising both maternally and paternally derived chromosomes. Cold or hydrostatic pressure treatments to inhibit the second polar body release after above-mentioned hybridizations induced "allotriploidy" with two sets of maternal chromosomes and one set of paternal chromosome. Hybridizations between female tetraploid spinous loach (4n=96) and male carp and those between female tetraploid loach (4n=100) and male carp also produced "allotriploidy". Artificial inhibition of the second polar body release after these hybridizations with pressure shock produced "allopentaploidy" with four sets of spinous loach or loach chromosomes and one set of carp chromosome. External appearances of deformed larvae seemed to be improved by allopolyploidization, but no surivors were obtained