A biometrical genetic model is presented for the analysis of quantitatively varying diploid inherited traits which are expressed in a triploid phase. It shows that gene dispersion and ambidirectionality influences virtually all the components of means and at least four components of variances. Consequently, separate parameters are needed to describe the genetic variation among the second-degree statistics of the selfing and the backcrossing series. It is further shown that the effects of maternal/cytoplasmic inheritance can be separated from those of the nuclear genes both by the scaling tests and by the weighted least squares method. The applicability of the model to experimental data is demonstrated by analysing the amylose content of the generations derived from a cross between two pure breeding lines of rice.

Amylose content has a pronounced effect on the cooking and eating quality of rice (Oryza sativa L.). Inheritance of amylose content in five crosses of rice and their reciprocals involving low, intermediate, and high amylose parents was studied. The analysis was based on single grains in the parent, F1, F2, B1F1 and B2F1 generations. The genes for high amylose content were found to be completely dominant over those for low or intermediate amylose content. Low or intermediate amylose content in the crosses tested was found to be governed by a single gene having a major effect. Evidence that amylose content was also influenced by genes of minor effects, or modifiers, was also noted. The role of dosage effects in influencing segregation was stated and breeding strategies are discussed.

Seven indica rice varieties with different amylose contents were crossed in all possible combinations including reciprocals. Single grains of parents and F1's were analyzed to determine the dosage effects of genes responsible for different amylose contents. Different genes for amylose content showed differential effects on endosperm appearance and amylose production in the F1. A single dose of very low or low amylose gene was not capable of producing amylose to the level of their non-waxy parent in waxy/non-waxy crosses. The effect of one dose of gene for intermediate or high amylose was highly conspicious with relatively less dosage effect. Dosage effects were observed in both waxy/non-waxy and among non-waxy crosses. In general, amylose content increased with increase in gene dosage though not in a linear fashion. Cases where amylose content decreased with increase in dosage for higher amylose have also been observed. The importance of such results in understanding the inheritance pattern of this trait has been discussed.

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Models of Pooni et al. (1992) were employed to investigate the genetic control of amylose content in 10 rice crosses produced by the pairwise crossing of five varieties representing almost the whole range of amylose levels from 0 to 28 per cent. Analyses of the first-degree statistics revealed an important role of the additive and the dominance effects in determining the genetic variability in all the crosses. Epistasis and cytoplasmic effects were also observed to contribute significantly to the variability among the generation means of most crosses. Dominance was generally towards the higher score and its effects were enhanced by a complementary dominance x dominance interaction in several sets of basic generations.The predominantly additive nature of the genetic variability was further revealed by the analyses of second-degree statistics. Component D was detected significant in all the crosses while components H1 and H2 were non-significant throughout. Significance of the covariance components F' and F", however, showed indirectly that dominance contributed significantly to variability at the variance level. Higher levels of transgression and considerable increases in the phenotypic ranges displayed by the segregating generations of various crosses, also pointed to their potency for yielding superior recombinants with diverse levels of amylose.

Inheritance of waxy locus was studied in crosses of a waxy variety with four non-waxy parents having high-, intermediate-, low- or very low-amylose content. The analysis for amylose content was done on a single grain basis in parents, F1, F2, B1F1, and B2F1 seeds. The waxy parent lacking synthesis of amylose content was found to differ from the ones having high-, intermediate-, low- or very low-amylose content by one gene with major effect. Dosage effects for amylose content were observed to have great influence on segregation pattern and efficiency of selection. Selection efficiency for amylose content can be enhanced by selecting for endosperm appearance in early segregating generations.