Estimate of the Number of Genes involved in the Genetic Suppression of the Cytological Diploidization of Wheat

Abstract

Triticum aestivum is an allohexaploid species originating from the hybridization of a tetraploid wheat and the diploid species Aegilops squarrosa. The tetraploid wheats are also allopolyploid species and were derived from a hybrid between a diploid wheat species and the diploid Ae. speltoides. The relationship of these three diploid species is such that, in hybrids between them, at first meiotic metaphase there is an average of approximately 3.5 bivalents from a possible maximum of seven¹. On this basis some multivalent formation would be expected in amphidiploids derived from them, yet the usual meiotic disturbance in hexaploid wheat is univalent formation². Classically, the regular bivalent formation and absence of intergenomic pairing in the polyploid Triticum species has been explained in terms of differential affinity, and in recent years it has been shown that differential affinity is enhanced by the activity of a genetical system on the long arm of chromosome 5B (refs. 3, 4).