Figure 2.

Segregation of mea alleles in a duplex tetraploid. In tetraploids, the frequencies of the different gamete classes depend on the coefficient of double reduction, c, which is the frequency at which the alleles of two sister chromatids are recovered in the same gamete (Burnham 1962). (Small boxes) Haploid genomes from mutant mea-1 (red) or wild-type MEA (yellow) alleles. For the chromosomal region containing the mea locus, c has been estimated as c = 0.1 (van der Veen et al. 1973). In duplex tetraploids, the frequencies of MEA/MEA, MEA/mea-1, and mea-1/mea-1 gametes are (1 + 2c)/6 = 0.2, 4(1 − c)/6 = 0.6, and (1 + 2c)/6 = 0.2, respectively. These values were used to calculate the frequencies of the different endosperm classes that receive two maternal and one paternal genome. If the maternal genotype determines the seed phenotype independent of gene dosage, we expect endosperm genotypes with at least one maternal wild-type MEA allele to develop normally amounting to 78.8% of the seeds [adjusting for a spontaneous seed abortion rate of 1.5% as determined for the parental tetraploid; (0.04 + 0.12 + 0.04 + 0.12 + 0.36 + 0.12) × (100 − 1.5)% = 78.8%]. If normal seed development depends on an excess of wild-type MEA product independent of parental origin in the endosperm we expect endosperm genotypes with MEA:mea-1 > 3:3 to develop normally amounting to 31.5% of the seeds [(0.12 + 0.04 +0.12 + 0.04) × (100 − 1.5)% = 31.52%].