Aneuploidy

Abstract

The terms 'haploid' and 'diploid' that describe single (n) and double (2n) chromosome sets in cells were coined by the Polish-German botanist Eduard Strasburger and originate from the Greek terms haplóos meaning 'single' and diplóos meaning 'double'. The term 'ploidy' was subsequently derived to describe the total chromosome content of cells. Consequently, the term 'euploid' refers to a chromosome complement that is an exact multiple of the haploid number. Therefore, haploids and diploids are both cases of normal euploidy. Euploid types that have more than two sets of chromosomes are 'polyploid' such as 'triploid' (3n), 'tetraploid' (4n), 'pentaploid' (5n), and so forth. There are various natural euploid states with some organisms existing as haploids (fungi), diploids (most mammals), and polyploids (plants).Cells rely on precise mechanisms to ensure accurate chromosome segregation during mitosis and meiosis to maintain their euploid state. Errors in the faithful execution of these mechanisms cause chromosome mis-segregation resulting in the generation of 'aneuploid' (i.e. 'not euploid') daughter cells. Aneuploidy is defined as a chromosome number that deviates from a multiple of the haploid set, and it is associated with abnormalities in cell function, such as in cancer and in organismal development such as in Down syndrome and mosaic variegated aneuploidy (MVA) (Figure 1). Aneuploidy reflects both gains/losses of whole chromosomes, leading to 'whole chromosomal' aneuploidy, as well as non-balanced rearrangements of chromosomes, including deletions, amplifications or translocations of large regions of the genome resulting in 'structural' aneuploidy. Here, we discuss the causes of aneuploidy (Figure 2) and the consequences of aneuploidy on cells and organisms.

New insights into the karyotype evolution of the free-living flatworm Macrostomum lignano (Platyhelminthes, Turbellaria)

“…For example, studies of aneuploidy in model species from different taxa (plants, invertebrates, mammals) have revealed that aneuploidy has severe effects on development and growth 18, 37–39 , and in humans, aneuploidy is associated with abnormalities in cell function (including cancer) and organismal development 40 .…”

Quantitative methods to measure aneuploidy and chromosomal instability

“…Aneuploidy is defined as a state of abnormal chromosome numbers that deviates from a multiple of the haploid complement. In addition, structural aneuploidy arises from DNA damage that causes translocations, duplications or deletions of chromosomal regions (Orr, Godek, & Compton, 2015). Whole chromosome aneuploidy and structural aneuploidy are linked as whole chromosome segregation errors can lead to DNA damage and structural rearrangements (Janssen, van der Burg, Szuhai, Kops, & Medema, 2011).…”

“…Chromosome segregation errors result in constitutional, constitutive, or mosaic aneuploidies (Orr et al, 2015). Constitutional aneuploidy is an abnormal karyotype that is present in all cells.…”

“…Constitutional aneuploidy is an abnormal karyotype that is present in all cells. Down syndrome is an example of constitutional aneuploidy that most frequently occurs due to meiotic errors and results in trisomy for chromosome 21 present in all cells of an individual with the condition (Hassold & Hunt, 2001; Orr et al, 2015). Constitutive aneuploidy is an abnormal but stable karyotype that generates a homogeneous sub-population of aneuploid cells (Orr et al, 2015).…”

“…Down syndrome is an example of constitutional aneuploidy that most frequently occurs due to meiotic errors and results in trisomy for chromosome 21 present in all cells of an individual with the condition (Hassold & Hunt, 2001; Orr et al, 2015). Constitutive aneuploidy is an abnormal but stable karyotype that generates a homogeneous sub-population of aneuploid cells (Orr et al, 2015). Mosaic aneuploidy is abnormal and unstable karyotypes that generate a heterogeneous sub-population of aneuploid cells (Orr et al, 2015).…”