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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