1. What species are considered to be wheat?

The cereal known as wheat comes from several closely related species. Four of these species are cultivated: einkorn (Triticum monococcum ssp. monococcum), emmer (T. turgidum ssp. durum), timopheevii (T. timopheevii ssp. timopheevii) and common or bread wheat (T. aestivum).

2. How does the genome of common/bread wheat(Triticum aestivum) differ from other species of wheat and what is the relationship between them?

Common/bread wheat(Triticum aestivum) is a disomic allohexaploid (AABBDD genomes). It arose from the convergence of three diploid ancestors that have diverged from a common ancestor and coevolved some 2.5 to 4.5 million years ago. Approximately 0.5 million years ago, the diploid wheats T. urartu (AA genomes) and Aegilops speltoides (SS genomes, most closely related to the B genome) hybridized to form the tetraploid wheat T. turgidum (AABB), which includes durum wheat. About 8,000 years ago T. turgidum hybridized with the wild diploid goatgrass Aegilops tauschii (DD genomes) to form bread wheat. Mapping studies using cDNAs and ESTs as RFLP probes indicate that the three genomes of hexaploid wheat carry, in general, the same genes at the same relative positions along homoeologous chromosomes, aside from a few well-known large translocations, and probably many other still unknown local rearrangements.