Modern varieties of wheat are the result of hybridisation of different varieties of wheat over 10,000 years.Hybridisation is the combining of genes of different varieties or species of organism to produce polyploid hybrids.Polyploidy may arise if chromosomes do not separate into two distinct sets during meiosis. Zygotes from the fertilised gametes will therefore have 3 or more sets of chromosomes.Cross-pollination can also lead to hybridisation of two separate species. Hybrids are usually sterile because meiosis cannot take place unless homologous chromosomes can pair during prophase and metaphase.If the chromosome number is a multiple of the original chromosome number meiosis is possible and the hybrid will be fertile.Modern wheat plants may be the result of Einkorn wheat with 14 chromosomes hybridising with Aegilops speltoides a goat grass also with 14 chromosomes. This gave rise to a hybrid species called Emmer wheat. Further hybridisation with Aegilops tauschii which had 14 chromosomes gave rise to the modern wheat Triticum aestivum.