Chromosome number and morphology
In several topics of genetics on Biocyclopedia.com, examples from human beings were utilized wherever available. However, the technique, developed by J.H. Tjio and A. Levan in 1956, enabled the determination of correct chromosome number (2n = 46) in human beings for the first time. Later, on the basis of morphology, twenty three chromosomes in human beings were arranged in seven groups (Table 24.1). Chromosomes of a human male at metaphase are shown in Figure 24.1. From such photographs, karyotypes are prepared according to the arrangement shown in Table 24.1.