ISOZYME ANALYSIS OF PROGENY DERIVED FROM (ALLIUM-FISTULOSUM X ALLIUM-CEPA) X ALLIUM-CEPA

Relatively large quantities of seed were obtained from the interspecific backcross (A. fistulosum x A. cepa) x A. cepa allowing, for the first time, an extensive study of the heritable traits exhibited by backcross progeny. Two backcross populations, BC1034 and BC1040, distinguished by different A. fistulosum parents, were characterized for the isozyme markers Idh-1, Adh-1. and Pgi-1. Statistical methods are described to calculate cell probabilities for a mixed population of F2 and BC1 progeny, using an estimate of the fraction of F2 progeny in the population derived from the isozyme data. Cell probability distributions were calculated for a mixed population with independent pairs of loci and a mixed population with nonindependent pairs of loci. The isozyme loci Idh-1 and Pgi-1 appear to be linked, with a map distance estimated at 33 centimorgans (cM) in BC 1 034 and 42 cM in BC 1 040. The probability distribution model for linked loci did not account for all of the distorted segregation ratios in Idh-1 x Adh-1 or Pgi-1 x Adh-1. The cytological literature does not support linkage between Idh-1 x Adh-1 or Pgi-1 x Adh-1. The distorted segregation ratios for these pairs of loci are likely the result of genetic incompatibilities between the two species.