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In the germ-line (the sex cells) the chromosome number is n (humans: n = 23). So, in normal diploid organisms, autosomal chromosomes are present in two copies. Polyploid cells have multiple copies of chromosomes and haploid cells have single copies.

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But, used in conjunction with other phylogenetic data, karyotypic fissioning may help to explain dramatic differences in diploid numbers between closely related species, which were previously inexplicable.It is New Latin from Ancient Greek κάρυον karyon, "kernel", "seed", or "nucleus", and τύπος typos, "general form").The next stage took place after the development of genetics in the early 20th century, when it was appreciated that chromosomes (that can be observed by karyotype) were the carrier of genes.Lev Delaunay is applied after cells have been arrested during cell division by a solution of colchicine usually in metaphase or prometaphase when most condensed.In order for the Giemsa stain to adhere correctly, all chromosomal proteins must be digested and removed.The low record is held by the nematode Parascaris univalens, where the haploid n = 1; and an ant: Myrmecia pilosula.

The existence of supernumerary or B chromosomes means that chromosome number can vary even within one interbreeding population; and aneuploids are another example, though in this case they would not be regarded as normal members of the population.

Although the replication and transcription of DNA is highly standardized in eukaryotes, the same cannot be said for their karyotypes, which are highly variable.

There is variation between species in chromosome number, and in detailed organization, despite their construction from the same macromolecules.

Attention is paid to their length, the position of the centromeres, banding pattern, any differences between the sex chromosomes, and any other physical characteristics.

The study of whole sets of chromosomes is sometimes known as karyology.

and for a test that detects this complement or measures the number.