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Exploring the potential of gametic reconstruction of parental genotypes by F1 hybrids as a bridge for rapid introgression1

Cannon, Charles H., Scher, C. Lane
Genome 2017 v.60 no.9 pp. 713-719
DNA, Quercus, backcrossing, chromosome number, chromosomes, gametophytes, gene flow, genomics, genotype, germ cells, hybrids, interspecific hybridization, introgression, meiosis, phenotype, pollen, progeny, trees
Interspecific hybridization and genetic introgression are commonly observed in natural populations of many species, especially trees. Among oaks, gene flow between closely related species has been well documented. And yet, hybridization does not lead to a “melting pot”, i.e., the homogenization of phenotypic traits. Here, we explore how the combination of several common reproductive and genomic traits could create an avenue for interspecific gene flow that partially explains this apparent paradox. During meiosis, F₁ hybrids will produce approximately (½)ⁿ “reconstructed” parental gametes, where n equals the number of chromosomes. Crossing over would introduce a small amount of introgressive material. The resulting parental-type gametophytes would probably possess a similar fertilization advantage as conspecific pollen. The resulting “backcross” would actually be the genetic equivalent of a conspecific out-cross, with a small amount of heterospecific DNA captured through crossing over. Even with detailed genomic analysis, the resulting offspring would not appear to be a backcross. This avenue for rapid introgression between species through the F₁ hybrid will be viable for organisms that meet certain conditions: low base chromosome number, conserved genomic structure and size, production of billions of gametes/gametophytes during each reproductive event, and conspecific fertilization advantage.