Multilocus Interactions Restrict Gene Introgression in Interspecific Populations of Polyploid Gossypium (Cotton)

Abstract

.— Experimental advanced‐generation backcross populations contain individuals with genomic compositions similar to those resulting from interspecific hybridization in nature. By applying a detailed restriction fragment length polymorphism (RFLP) map to 3662 BC3F2 plants derived from 24 different BC1 individuals of a cross between Gossypium hirsutum and G. barbadense, large and widespread deficiencies of donor (G. barbadense) chromatin were found, and seven independent chromosomal regions were entirely absent. This skewed chromatin transmission is best accounted for by multilocus epistatic interactions affecting chromatin transmission. The observed frequencies of two‐locus genotypes were significantly different from Mendelian expectations about 26 times more often than could be explained by chance (P≤ 0.01). For identical pairs of loci, different two‐locus genotypes occurred in excess in different BC3 families, implying the existence of higher‐order interlocus interactions beyond the resolution of these data. Some G. barbadense markers occurred more frequently than expected by chance, indicating that genomic interactions do not always favor host chromatin. A preponderance of interspecific allelic interactions involved one locus each in the two different subgenomes of (allotetraploid) Gossypium, thus supporting several other lines of evidence suggesting that intersubgenomic interactions contribute to unique features that distinguish tetraploid cotton from its diploid ancestors.

Loci Affecting Long-Term Hybrid Survivorship in Louisiana Irises: Implications for Reproductive Isolation and Introgression

“…First, heterospecific alleles may be acting to increase survivability when present, resulting in plants that survive having a higher proportion of heterospecific versus conspecific alleles. Positive selection for donor genetic material has been postulated from other studies of Louisiana irises (Burke et al 1998), and for cotton (Wang et al 1995;Jiang et al 2000), sunflower (Rieseberg et al 1996), and Eucalyptus (Myburg et al 2004). Second, our findings may also be explained by inbreeding depression caused by our crossing design (discussed in Bouck 2004), or genetic load harbored by I. brevicaulis and I. fulva individuals.…”

“…The advent of molecular marker techniques has allowed for the dissection of the genetic basis of polygenic traits (Lander and Botstein 1989;Tanksley 1993;Zeng 1994), including that of hybrid fitness. Further, the construction of genetic linkage maps in several plant systems (Rieseberg et al 1993;Bert et al 1999;Remington et al 1999;Lespinasse et al 2000;Peng et al 2000;Ramsay et al 2000;Fishman et al 2001;Bouck et al 2005) has made it possible to measure differential rates of introgression of parental alleles into hybrid genomes (Rieseberg et al 1995;Jiang et al 2000). This in turn has led to the identification of regions of the genome more (or less) likely to introgress between hybridizing taxa (e.g., Rieseberg et al 1999).…”

A Linkage Map Reveals a Complex Basis for Segregation Distortion in an Interpopulation Cross in the Moss Ceratodon purpureus

“…Lethal DM interactions also result in a correlation between allelic states at the interacting loci ( Jiang et al 2000;Payseur and Hoekstra 2005). This is because the A NY and B Ec alleles in the preceding example are found only with the homospecific complementary allele, but never together (e.g, the A NY allele is found only with the B NY , and the B Ec allele is found only with the A Ec ).…”

Ancestry Influences the Fate of Duplicated Genes Millions of Years After Polyploidization of Clawed Frogs (Xenopus)

“…In these genomes, natural selection and stochastic processes govern the genetic fate of each paralog-fates that include redundancy, subfunctionalization, neofunctionalization, and gene silencing (Ohno 1970;Hughes and Hughes 1993;Force et al 1999;Lynch and Force 2000;Lynch et al 2001;Gu 2003). After allopolyploidization, interactions between the subgenomes derived from each ancestral species included exchange of chromosome segments (Moscone et al 1996;Skalická et al 2005), concerted evolution (Wendel et al 1995;Volkov et al 1999), recombination (Zwierzykowski et al 1998), and epistasis ( Jiang et al 2000). Restructuring can then alter the stoichiometry of protein interactions by modifying regulatory elements or changing gene copy number.…”