Evidence for multilocus genetic control of preferential fertilisation in maize

Genetic segregation was studied in more than 1900 seedlings of an F 2 between the maize ( Zea mays L.) inbred lines T232 and CM37. Significant segregation distortion was observed at 11 of 17 segregating allozyme loci and at a single morphological marker locus distributed on 7 of the 10 chromosomes in the genome. Deviations from genotypic class expectations were small for most loci, and averaged 7·7 per cent. Percent transmission of the allele contributed by T232 varied from 47·7 per cent to 53·3 per cent. The allele donated by T232 was significantly under-represented for loci on chromosomes 1 and 8, whereas the allele contributed by CM37 was deficient for nine of the ten segregating loci on chromosomes 2, 3, and 6. In all cases, the parental origin of the deficient allele was consistent for markers on a chromosome. Evidence is presented that suggests the aberrant ratios arose from linkage of the markers with genetic factors affecting prezygotic transmission, and that a minimum of 5 such factors were operative, one on each of chromosomes 1, 2, 3, 6, and 8. In contrast to the multi-locus and multi-chromosomal distorted segregation observed in the F 2 , all loci in backcross progenies fit Mendelian expectations. It is suggested that this discrepancy reflects variable environmental selection pressures on genes that influence aspects of gamete competition.