Genomic analysis also has shown that one of the important mechanisms of evolution is multiplication of chromosome sets, resulting in polyploidy (“many genomes”). In plants and animals, spontaneous doubling of chromosomes can occur. In some plants, the chromosomes of two related species unite via cross-pollination to form a fusion product. This product is sterile because each chromosome needs a pairing partner in order for the plant to be fertile. However, the chromosomes of the fusion product can accidentally double, resulting in a new, fertile species. Wheat is an example of a plant that evolved by this means through a union between wild grasses, but a large proportion of plants went through similar ancestral polyploidization.