Abstract

SAHAGUN-CASTELLANOS, Jaime. Genetic stability of synthetics derived from double-cross or three-way line hybrids. Rev. Chapingo Ser.Hortic [online]. 2015, vol.21, n.2, pp.147-155. ISSN 2007-4034.  https://doi.org/10.5154/r.rchsh.2014.04.017.

In the development of the theory of synthetic varieties (SVs) of crop species such as maize (Zea mays L.) and onion (Allium cepa L.), formed with single-cross hybrids, it has been shown that genetic erosion may occur during their formation. This erosion increases inbreeding and reduces yield. This gene loss is caused by the mating of heterozygous genotypes, the finite number of their progeny, and the randomness of the genetic mechanism. The main objective of this study was to determine the number of non-identical by descent (NIBD) genes lost during the development of the individuals that represent the double-cross (DC) or three-way (TW) line hybrids that in turn will be parents of a SV. The initial lines were assumed to be inbred and unrelated and each hybrid derived from them was represented by m individuals, and formulae for the mean, variance and number of lost NIBD genes per hybrid were derived. The number of lost NIBD genes of a DC (TW) was expressed as the number of NIBD genes in the 4 (3) initial lines minus the mean of NIBD genes forming the genotypes of the m individuals representing each DC (TW). It was found that each DC and TW loses on average 4/2^m and 2/2^m NIBD genes, respectively. The magnitudes of these losses reflect the effect of the sample size (m) and the number of loss sources (the single crosses) of the parents of the DCs (2) and TWs (1). The largest NIBD gene losses per parent were 2 (DC) and 1 (TW), which occur when m = 1. However, when m is large (m ≥ 12), as should occur in reality, the losses and the variance of the number of NIBD genes are nearly zero.

Keywords : Zea mays L.; Allium cepa L.; non-identical by descent genes; inbreeding coefficient; genotypic mean.

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