mostly
allopolyploids as discussed below in "Polyploidy--DNA
Neopolyploids are documented recent
allopolyploids with chromosome numbers that are multiples of the lowest number presently known for their evolutionary group; whereas, paleopolyploids are assumed to be ancient
allopolyploids that have the lowest known chromosome numbers for their evolutionary group.
Discussing in turn the genomics of hybrids and of polyploids, and mechanisms for novelty in the two, they consider such topics as transcriptome profiling of Drosophila inter-specific hybrids, developments in the study of the genomics and heterosis in hybrid rice, chromosomal and gene expression changes in Brassica
allopolyploids, polyploid species-specific chromosomal polymorphisms in wheat, seed development in interploidy hybrids, and genetic and epigenetic mechanisms for polyploidy and hybridity.
The genus Mangifera comprises 69 species (BOMPARD, 2009) and based on some chromosome counts and meiotic analyses these are considered ancient
allopolyploids.
Certainly,
allopolyploids are a sizable fraction of well-studied crop cases, such as wheat, cotton, maize, sugar cane, coffee, and tobacco.
2001) studied the rate and time of elimination of several low-copy DNA sequences, existing at diploid level, in F1 hybrids and newly formed
allopolyploids of Aegilops and Triticum.
Lande and Schemske (1985) showed that the difference in inbreeding depression between diploids and tetraploids should hold for both autopolyploids and
allopolyploids when mutations are recessive and lethal or sublethal.
Stebbins (1942, 1947) early championed the value of
allopolyploids in understanding plant biogeography.
This situation contrasts to other
allopolyploids such as cotton, which has SY QTL in homoeologous regions of both subgenomes (Saranga et al.
Allopolyploids arise through hybridization between two chromosomally differentiated taxa (Stebbins 1950; White 1973, 1978; Stace 1980; Grant 1981).
Most of the perennial grass species in the tribe Triticeae are
allopolyploids that originated from genome combinations of two or more species.
In contrast, the absence of multivalents in
allopolyploids makes the hybrids less sterile and more competitive (Briggs & Walters, 1984); this increases their dispersal and their chances of being established as a new species.
