Many plant cells have more than two complete sets of chromosomes in each cell. Explain how this might occur.

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Allopolyploidy. Basically, since plants rely on external agents (such as wind, birds and insects) to transport their pollen from one plant to another, they have no control where their pollen may end up. Their pollen often end up on the stamen of a different species. Therefore interspecific hybridization can be quite common, more common in plants than in animals, since animals can use behavioral means to minimize hybridization (e.g. a bird can make sure that it is mating with an individual of the same species before agreeing to mate). Interspecific hybrids are often sterile since they have two different half sets of chromosomes and these chromosomes do not line up during meiosis. One way to get around this problem is to duplicate both sets of chromosomes using a process called allopolyploidy. That is why some plant cells may have two complete, but different, sets of chromosomes in each cell.

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