Polyploidy

= Polyploidy = Polyploidy is when a cell or an organism has more than two homologous sets of chromosomes. It occurs very often in plantsso that 30-80% of plant species are polyploid. It's less common in animals, but there are a few examples, like leeches, flatworms, mole salamanders. There has probably been polyploidy in the evolutionary history of all eukaryotic organisms, which is referred to as paleopolyploidy. In humans, polyploidy occurs in 2-3% of pregnancies and causes 15% of miscarriages. If the fetus does survive to birth, it dies soon afterwards.

Polyploid crops tend to be larger and flourish better in farm fields, meaning that many crops have been unwittingly bred to be polyploids. Wheat has a diploid strain, a tetraploid strain, (4 sets) and a hexaploid strain (6). Some polyploid crops are valued because they are sterile, and therefore seedless. They reproduce asexually, like by grafting. Apples, bananas, and citrus fruits produce viable seeds in the wild, but the ones grown by people are triploid, which means the three sets of chromosomes cannot divide evenly. They're also grafted, meaning that all Granny Smith apples, for example, are genetically identical.

Hybrids
Another use of polyploidy is to give sterile hybrids the ability to reproduce themselves. For example, triticale is a hybrid of wheat and rye, that at first has two sets of wheat chromosomes, and one set of rye chromosomes. Because that makes it triploid, it is sterile. However, when treated with colchicine, the sets double, giving it four sets of wheat and two sets of rye, and making it able to reproduce.