An Investigation on Variability of Coefficient of Coancestry of Rice (Oryza sativa L.)

Selection and genetic drift during inbreeding may cause parental genomic contribution to progenies deviate from the expected values; therefore, it affects the value of coefficient of coancestry (f). This study used Simple Sequence Repeat markers to estimate the distribution of parental contribution in three F4 rice populations. Each expected parental contribution was substituted by random variables from these distributions in 637 joponica rice pedigrees of Taiwan. After 200 times simulations, we observed that the means of 200 simulative f are fairly close to that of the expected f (R2＝0.997). The standard deviations (SD) and means of 200 simulative f were not correlated with number of lines in the pedigree, number of common ancestors, number of crosses involved and maximum generations of the pedigrees. However, there was a relationship between the logarithmic mean and the logarithmic SD (R2=0.939). Confidence intervals (CIs) of f were fitted by the log-liner model and Beta distribution. The largest difference between CIs and simulative f was 0.16. Moreover, assigning common ancestors with a larger f may raise the value of final f, but has small effect on relationships among tested lines.