Wild diploid wheat has seven chromosomes in its pollen. Discuss the major events that had to occur for tetraploid pasta wheat to have evolved. Describe the genome and fertility of pasta wheat (number and kinds of chromosomes).

Tetraploid wheat evolved by allopolyploidization and subsequent diploid-like behavior due to cytological diploidization

Explanation:

Durum wheat (Triticum durum) or pasta wheat, is a tetraploid wheat species that has 28 chromosomes, i.e., seven pairs in each genome (2n = 4x = 28). Durum wheat was domesticated from wild emmer wheat, which originated by hybridization of two diploid wheat species with 14 chromosomes: Triticum monococcum (genome AA) and one wild progenitor (genome BB). Triticum durum is a typical example of evolution by hybridization and polyploidization, where the resultant tetraploid species has two complete sets of chromosomes. Allopolyploidization is one of the most common types of plant speciation. During meiosis, 28 chromosomes form 14 homologous chromosome pairs, because homologous chromosomes have developed 'restriction of pairing' (i.e., cytological diploidization). The restriction of pairing to fully homologous chromosomes ensures a correct meiotic behavior, which otherwise would be altered due to the high level of homology that still exists among chromosomes from different wheat progenitors.