Ploidy/Aneuploidy/Polysomy

                 Ploidy is the number of chromosomes per set in a cell. In eukaryotes, we usually find two types of sets: Haploid organisms composed only for one chromosome per set and diploid organisms which have two chromosomes per set in each cell. Consequently, the germ cells of a diploid or a haploid organism will originate other organisms that will be diploid and haploid, respectively, at least in one stage of their life.

                Aneuploidy is a genetic disorder related with the number of chromosomes in a cell. This anomaly occurs, normally, in the development of the gametes, non-disjunction of homologous chromosomes during meiosis or problems in the random distribution of chromosomes or even in crossing-over. These mutated chromosomes have a number of chromosomes per set that weren’t “suppose” to have, more or less than expected.

               Polysomy is a type of aneuploidy in which a set of chromosomes has more chromosomes than it would be normal to have, for example, in a diploid organism, a set of chromosomes with more than a pair is a case of polysomy. It is usually classified by the number of chromosomes per set, for example, a polysomy with three chromosomes is called a trisomy, a polysomy with four chromosomes is called tetrasomy and so on.