Answer:
Tetraploid wheat evolved by allopolyploidization and subsequent diploid-like behavior due to cytological diploidization
Explanation:
Durum wheat (<em>Triticum durum</em>) 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: <em>Triticum monococcum</em> (genome AA) and one wild progenitor (genome BB). <em>Triticum durum </em>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.
<span>The exosphere is the fifth and final layer of the atmosphere. This layer is a little thicker than the theremosphere at 500-1000 km thick.</span>
