By applying half-tetrad analysis to segregating tetraploid progeny that had been raised from 2x–4x and 2x–2x crosses, five marker loci (ym, y, Got-1, Got-2, and ds-1) were mapped to their respective centromeres in male and female meiosis of both normal synaptic and desynaptic (ds-1ds-1) diploid potato clones. Significant sex differences in genetic recombination for these loci did not occur in either normal plants or desynaptic mutants, which suggests that genetic exchange in both the sexes is governed by the same control system. In desynaptic mutants a severe reduction in crossing-over was observed for ym and.y (83.7 an 90.0% reduction, respectively), whereas recombination rates for Got-2 appeared to have systematically, although not significantly, increased. The ds-1 gene was concluded to substantially reduce the overall chiasma frequency and to differentially alter chiasma distribution along individual chromosomes. Based on segregation ratios in progeny from different types of testcrosses, first division restitution (FDR) and second division restitution (SDR) 2n gametes formed by normal synaptic plants were estimated to transmit on average about 82.7 and 36.1 %, respectively, of the parental heterozygosity to tetraploids. With desynapsis the average amount of heterozygosity transmitted by FDR 2n gametes amounted to 94.1%. SDR 2n gametes from desynaptic mutants are sterile as a result of aneuploidy. The ds-1 gene was demonstrated to particularly enhance the ability of FDR 2n gametes to preserve the genetic constitution of diploid parental clones with a minimum amount of reassortment. The potential value and limitations of the ds-1 gene for the production of true potato seed varieties and the experimental induction of diplosporic apomixis are discussed.Key words: Solanum, genetic markers, gene–centromere mapping, desynapsis, reduced recombination.
Genetic correlation between biomass allocation to male and female functions in a natural population of Ipomopsis aggregata