Evolution Of Polyploid Species Research Articles

Phylogenetic analysis of Gossypium L. using restriction fragment length polymorphism of repeated sequences.

Cotton is the world's leading textile fiber crop and is also grown as a bioenergy and food crop. Knowledge of the phylogeny of closely related species and the genome origin and evolution of polyploid species is significant for advanced genomics research and breeding. We have reconstructed the phylogeny of the cotton genus, Gossypium L., and deciphered the genome origin and evolution of its five polyploid species by restriction fragment analysis of repeated sequences. Nuclear DNA of 84 accessions representing 35 species and all eight genomes of the genus were analyzed. The phylogenetic tree of the genus was reconstructed using the parsimony method on 1033 polymorphic repeated sequence restriction fragments. The genome origin of its polyploids was determined by calculating the diploid-polyploid restriction fragment correspondence (RFC). The tree is consistent with the morphological classification, genome designation and geographic distribution of the species at subgenus, section and subsection levels. Gossypium lobatum (D7) was unambiguously shown to have the highest RFC with the D-subgenomes of all five polyploids of the genus, while the common ancestor of Gossypium herbaceum (A1) and Gossypium arboreum (A2) likely contributed to the A-subgenomes of the polyploids. These results provide a comprehensive phylogenetic tree of the cotton genus and new insights into the genome origin and evolution of its polyploid species. The results also further demonstrate a simple, rapid and inexpensive method suitable for phylogenetic analysis of closely related species, especially congeneric species, and the inference of genome origin of polyploids that constitute over 70% of flowering plants.

Recombinant genome of cereals: The pattern of formation and the role in evolution of polyploid species

The pivotal-differential model of evolution of polyploid species of cereals has been experimentally reproduced, and the pattern of the formation of a recombinant genome has been analyzed. It has been found that mutual substitution of chromosomes of the original genomes is subjected to selection pressure and, hence, is nonrandom. The selection occurs at the level of homeologs, whose selective advantages are determined by interactions between the genotype and the environment. If a homeolog has distinct selective advantages, the chromosomal composition of the corresponding homeologous group is completed rapidly, which leads to the formation of intergenomic recombination at the level of whole chromosomes. If homeologs have the same competitiveness, the composition of the group is stabilized more slowly. Domination of the genetic systems of the basic genome ensures a high rate of pairing of homeologous chromosomes of the recombinant genome during meiosis, which leads to recombinations at the level of chromosomal segments. It has been demonstrated that different combinations of chromosomes from original genomes are selected at different conditions of plant growth.

The role of 2n gametes and endosperm balance number in the origin and evolution of polyploids in the tuber-bearing Solanums.

Polyploidization has played a major role in the origin and evolution of polyploid species. In this article we outline the unique characteristics of 2n gametes and implications of their participation in the evolution of polyploid Solanum species. The genetic consequences of 2n gametes indicate that sexual polyploidization results in greater variability, fitness, and heterozygosity than does somatic doubling. Further, the mechanisms of 2n gamete formation and the frequency of 2n gamete-forming genes in present polyploids and their ancestral species provide additional evidence of their involvement. Equally important is the endosperm, via the endosperm balance number (EBN) incompatibility system, in complementing the role of 2n gametes. In fact, the EBN system acts as a screen for either 1n or 2n gametes, depending on the EBN and chromosome numbers of parental species. EBN in combination with 2n gametes maintains the ploidy integrity of diploid ancestral species, while providing the flexibility for either unilateral or bilateral sexual polyploidization.

Recurrent Addition of the Pennisetum americanum Genome in a P. americanum×P. orientale Hybrid

AbstractAn interspecific hybrid involving Pennisetum americanum (2 n = 14) and a diploid cytotype of P. orientale (2 n = 18) was backcrossed to P. americanum using the hybrid (2 n = 16, 7‘A’+ 9 ‘O’) as the female parent. Pollen mother cells of 13 BC1 plants contained a complement of 14‘A’+ 9 ‘O’ chromosomes. Five BC2 plants obtained through further backcrossing to P. americanum had 21‘A’+ 9 ‘O’ chromosomes revealing another addition of the P. americanum genome. The role of such recurrent additions of parental genomes in the evolution of polyploid species has been discussed.

HYBRIDIZATION BETWEEN AMPHIDIPLOIDS AND THE EVOLUTION OF POLYPLOIDS IN THE WHEAT(AEGILOPS-TRITICUM)GROUP

The polyploid species of the wheat group (genera A egilops and Triticum) are familiar as classical examples of evolution through amphidiploidy. The two genera have been a subject of extensive cytogenetic study by numerous workers (see reviews by Kihara, 1954, and Sears, 1948, 1959). The cytogenetic relations between the various diploid species in this group have been studied through interspecific crosses, and the polyploid species have been subjected to intensive genome analysis. On the basis of the cytological information gathered, Kihara ( 19 54) and Kihara et al. ( 19 59) established genomic formulae for the various A egilops species (table 1). Kihara concluded that the polyploid species of this group are typical allopolyploids and assumed that each polyploid species originated independently, as a result of an interspecific cross (or crosses) between two given diploid parental species followed by chromosome doubling. At present, the various polyploid species of the wheat group are generally regarded as well-established cases of such a mode of origin. The purpose of the present paper is to question the assumption of an independent evolution of the various polyploid species in the Aegilops-Triticum group. Evidence is presented to indicate that a considerable number of existing polyploids are genetically interconnected through hybridization and cannot be regarded to have evolved independently. The hypothesis is advanced that in addition to amphidiploidy, hybridization on the tetraploid level has played a decisive role in the evolution of the polyploid species. Tetraploid entities in the wheat group (as well as their modified genomes) are