Zoology · Ch 4 — Principles of Inheritance and Variation
Karyotyping
Karyotyping
Karyotyping is the technique of isolating an individual's complete chromosome set from a single cell and arranging the chromosomes into their homologous pairs for inspection; the resulting diagrammatic arrangement is itself called a karyotype (an idiogram is the more schematic, purely diagrammatic version of the same thing). Tjio and Levan, in 1960, worked out the practical method still used today: lymphocytes are cultured from a blood sample, mitosis is chemically induced, and colchicine is then added to arrest the dividing cells at metaphase — the stage at which chromosomes are maximally condensed and easiest to see individually. The resulting metaphase spread is photographed, and the individual chromosome images are then cut out and rearranged by hand (or digitally) into ordered homologous pairs; chromosome banding techniques additionally let structurally similar chromosomes be told apart with confidence. …
What this figure shows. A standard human male karyogram: 23 pairs of chromosomes cut from a metaphase spread photograph and arranged in homologous pairs in descending order of size, sorted into the classical groups A through G (with group C shown split by an additional labelled subgroup in the source figure), plus the non-homologous sex chromosome pair X and Y shown separately at one side, illustrating the male karyotype 44 autosomes + XY. No genetic data beyond chromosome group …