How to count chromosomes in a cell: An overview of current and novel technologies

Aneuploidy, an aberrant number of chromosomes in a cell, is a feature of several syndromes associated with cognitive and developmental defects. In addition, aneuploidy is considered a hallmark of cancer cells and has been suggested to play a role in neurodegenerative disease. To better understand the relationship between aneuploidy and disease, various methods to measure the chromosome numbers in cells have been developed, each with their own advantages and limitations. While some methods rely on dividing cells and thus bias aneuploidy rates to that population, other, more unbiased methods can only detect the average aneuploidy rates in a cell population, cloaking cell-to-cell heterogeneity. Furthermore, some techniques are more prone to technical artefacts, which can result in over- or underestimation of aneuploidy rates. In this review, we provide an overview of several "traditional" karyotyping methods as well as the latest high throughput next generation sequencing karyotyping protocols with their respective advantages and disadvantages.