A group of plants or animals comprising a species is characterised by a set of chromosomes, which have certain, constant features. These features include chromosome number, size and shape of individual chromosomes and other attributes listed above. The term karyotype is given to the group of characteristics that identifies a particular chromosome set and is usually represented by a diagram called idiogram, where chromosomes of haploid set of an organism are ordered in a series of decreasing size. The karyotypes of different groups are sometimes compared and similarities in karyotypes are presumed to represent evolutionary relationships.

Karyotype also suggests primitive or advanced feature of an organism. A karyotype showing large differences between smallest and largest chromosome of the set and having fewer metacentric chromosomes, is called asymmetric karyotype, which is considered to be a relatively advanced feature when compared with symmetric karyotypes. A symmetric and an asymmetric karyotype are shown in Fig. 6.10.