Vavilov’s Law of Homologous Series indicates that heritable variation for a given trait will occur in different species based on parallel selection. The conclusion comes from Vavilov’s study of extensive collections and careful attention to phenotypic variation across taxa. The same examination of variation can be applied to traits using the power of genetic and genomic resolution, because parallel traits would be expected to be governed by the same genetic loci, and perhaps even common mutations. In this review, these concepts are applied to two central traits—the control of “shattering” of kernels in cereals and in the control of photoperiodic flowering. One of the strengths of the law is that it can make predictions about traits and perhaps the genes or genomic regions that control them. With respect to genetic variation, the occurrence and physical location of genes associated with kernel retention may be predicted. Many grains share mutations, such as the Sh 1 gene, which were selected in parallel. Selection of the Sh1 gene led to higher yields due to better kernel retention. While the genes affected are often the same, the types of mutations are not, implying convergent selection. Flowering time is governed by multiple loci, so variation may be attributed only to a few candidates, yet because of the number of regulators the predictive power of the law is lower. The modern application of the Law of Homologous Series is that it allows basic researchers or plant breeders to make predictions about the genes controlling key traits, although the genetic basis of variation is likely not conserved.
The advantage of parallel selection of domestication genes to accelerate crop improvement
