Definition of Human chromosome count Human chromosome count: The
usual number of chromosomes in humans, 46 chromosomes. Also
called the human chromosome complement. History: For half a
century, the human chromosome count was widely believed to be
48. That changed on Dec. 22, 1955. On that day at the Institute
of Genetics of the University of Lund in Sweden, a visiting
scientist named Joe Hin Tjio (pronounced CHEE-oh) used what was
then a new technique to study the chromosomes of cells on a
glass microscope slide. The technique employed the drug
colchicine and a dilute salt solution. Colchicine froze the
cells at a point during division when the chromosomes had
separated into clearly visible bodies. The dilute salt solution
(hypotonic saline) spread the chromosomes so they could be seen
separately from one another. Tjio succeeded in obtaining a clear
picture of the human chromosome complement on a photomicrograph
(a photograph taken through a microscope) of a human embryonic
lung cell. Much to his amazement, T