Chromosomes and Karyotypes

Polyploidy

Some organisms and cells have entire sets of chromosomes additional to the standard 2N diploid. Cells that have extra sets in the formula of 3N are called triploid. If they are 4N, they are called tetraploid. This is different than the case of Down’s syndrome, which has a chromosome complement of 2N+1. Any time there are abnormal numbers of chromosomes, cells are referred to as aneuploid. A special case of aneuploid occurs from having entire sets more of chromosomes – polyploid. Plants are especially robust in the regard of polyploidy and often have different species arise in such a way. Some plants become sterile in the case of polyploidy and will not produce seeds properly.

Inside a wild-type banana
Wild bananas or plantains (Musa acuminata or Musa balbisiana) are deemed inedible because of their large seeds.
Have you ever seen a banana with these large seeds? The answer is most likely “No!” since these are not regarded as being edible. However, due to selective breeding practices, most edible plantains and bananas are hybrids of the two species Musa acuminata or Musa balbisiana that are 3N or 4N. In this case, the fruit are sterile and the seeds don’t develop. Other seedless fruit are also developed this way and require propagation through clonal means.

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