Human karyotype, 1920s (2N = 48 (?))
Left: Photomicrograph of cross-section of human
testis, showing spermatogonia in various stages of meiotic
and mitotic division. Right: Camera lucida drawing of
metaphase chromosome spread from previous slide. From
material such as this, Theophilus
Painter (1889 - 1969) counted the number of
human diploid chromosomes as 2N = 48. This number
was accepted until the 1950s, when better techniques of
chromosome spreading showed a correct count of 2N
= 46. (The difference is attributable to a
constriction in one chromosome pair that makes them appear
is two pairs joined end to end).
Figure © TC Hsu; Text material © 2020 by Steven M. Carr