The relationship between genetic and cytogenetic maps of pea. I. Standard and translocation karyotypes

A detailed cytogenetical study of inbred lines of pea and their F1 hybrids has been undertaken to study the relationship between the cytogenetic map and the molecular linkage map. The mitotic karyotypes of a standard pea line, JI15, a translocation line, JI61, and line JI281, a line used in the production of a mapping population, are given. A chromosome rearrangement detected by cytogenetic analysis of mitotic chromosomes has been further defined by synaptonemal complex (SC) analysis and the study of metaphase I chromosome behaviour. This meiotic analysis has allowed a comparison of SC physical lengths, observed chiasma frequencies, and recombination frequencies, as estimated from the genetic map, as a means of comparing physical and genetic distances.Key words: Pisum, linkage map, cytogenetics, chromosome rearrangement, synaptonemal complex.

Genetic control of Delia antiqua (Meigen) (Diptera: Anthomyiidae). Sensitivity to diapause interfering with a field-cage experiment using a homozygous chromosomal translocation

A translocation homozygous strain (TT) of Delia antiqua (Mg) was released into a field cage in Wageningen, The Netherlands, together with a standard laboratory strain (++). During the course of the season, the fecundity and fertility of the adults were measured together with the karyotype frequencies (TT+; T+; ++) of the F1 progeny. No selective disadvantage of the translocation karyotypes was observed. However, only four F1 adults emerged in the field cage; therefore a sample of pupae was removed from the cage, and it was shown that nearly 100% of the surviving pupae had entered diapause. This figure was confirmed from the remainder of the pupae. The fertility of eggs from the emerging adults was reduced to 54%, compared with the standard fertility of nearly 90%, but because of the diapause response of the strains used, the effect of this reduced fertility in the field-cage population could not be followed. The reasons for the change in diapause response of the laboratory strains are discussed and suggestions made as to how this could be prevented. The report highlights the importance of quality in control techniques involving translocations.