Aneuploidy vs Polyploidy
Chromosomes are the most important structures in a cell, and they are in the nucleus of a cell. Chromosome has two identical DNA molecules and they are called chromatids. These chromatids are bound together at a point called centromere. In a cell, chromosomes exist as pairs. These chromosome pairs are identical and, therefore, called homologous chromosomes.
Every organism has a particular set of chromosomes in each cell, and it is constant to an organism. In human, there are 23 homologous chromosomes and 22 of those are autosomes, which are not involved in sex determination, and the other pair of sex chromosomes is called allosomes.
Organisms that have two sets of homologous chromosomes are called diploid. Most of the species are diploid and symbolized as 2n. In higher plants, the sporophyte is diploid, and humans are also diploid. Organisms that have one set of chromosomes are called haploid, and symbolized by n.
Some organisms have more than two sets of chromosomes, and are called polyploidy. Most of the plant species show polyploidity, but rare in higher animals. Aneuploidy is produced by missing or adding particular chromosome or part of a chromosome. Both polyploidy and aneuploidy shows the abnormality of the chromosome number.
The alternation of chromosome number in a cell by adding or missing particular chromosome or chromosome set or part of a chromosome is called aneuploidy. So, chromosomal number differs from the wild type of the organism due to segregating defects.
According to the difference of the number of chromosome, there are several types of aneuploidy such as monosomy (2n-1), disomy (n+1), trisomy (2n+1) and nullisomy (2n-2) where the parent phenotype is 2n. Aneuploidy occurs mainly due to the failure of segregating chromosomes properly to the opposite poles in nuclear division i.e. in mitosis or meiosis, both sister chromatids or homologous chromosomes go to one pole, or in other words, none to other.
When a cell contains more than two sets of chromosomes, polyploidy occurs. So it alters the chromosome number in a cell. Polyploidy can be seen frequently in flowering plants including important crop plants but rarely in animals, except vertebrates and invertebrates.
Several types of polyploidy occur through several processes. Autopolyploidy is one type that is formed by multiplication of the genome of same species. Autopolyploidy is produced in sexual reproduction during meiosis by the non disjunction of homologous chromosomes in metaphase I or abnormal cell division in mitosis. Allopolyploidy occurs due to the combination of genomes of different species such as in hybrid species.
Polyploidy also can be induced using various chemicals such as colchicine by inhibiting cell division.
What is the difference between Aneuploidy and Polyploidy?
• The major difference between aneuploidy and polyploidy is that polyploidy occurs due to altering set of chromosome number such as 2n, 3n, 5n, whereas aneuploidy occurs due to altering particular chromosome or part of a chromosome such as 2n-1(monosomic).
• Aneuploidy can be seen in human as genetic disorders; for example, Tuner syndrome and Down syndrome, whereas polyploidy can be seen in some human muscle tissues.
• Aneuploidy is more common in human, whereas polyploidy is rare in human.
• Polyploidy can be seen in plants more common than aneuploidy.
1Griffiths AJF, Miller JH, Suzuki DT, et al. New York: W. H. Freeman; 2000. An Introduction to Genetic Analysis. 7th edition.