Inheritance and microsporogenesis of a synaptic mutant (sy-2) from Solanum commersonii Dun.

A mutant has been found in diploid Solanum commersonii (2n = 2x = 24) in which no bivalents are formed during microsporogenesis. This trait, a simply inherited recessive, has been designated sy-2. It conditions high levels of pollen sterility through random chromosome segregation at anaphase I. Only the nucleolar-associated chromosomes appear to segregate non-randomly, possibly due to the fusion of the nucleoli as cells near diakinesis. Branched spindle configurations result in multipolar telophase I arrangements, yielding from one to seven pollen grains at the tetrad stage. Most of the stainable pollen produced appears to be 2n. The 2n pollen formed by this mechanism should bear the exact genotype of the parent, since no crossing-over occurs.Key words: Solanum, potato, 2n gametes, mutants (meiotic), mutants (synaptic).