402
T . G. HSU
characteristic of normal females. Conversely, with Turner's syndrome
(Turner, 1938), the patients should be classified as sexually underdeveloped females. But as far as their sex chromatin is concerned, it is
negative, indistinguishable from normal males. These contradictory
cases found materialistic answers during recent years in the studies
of human chromosomes, as will be shown in the following section.
It is probably not unfair to say that today's booming mammalian
karyology is owing, to some extent, to my salesmanship (Editorial,
1959a) when I proposed the use of a hypotonic solution treatment
to spread the chromosomes of cells in vitro (Hsu and Pomerat, 1953).
This discovery of hypotonic solution treatment was purely accidental
in our laboratory (Hsu, 1952), then at The University of Texas Medical
Branch in Galveston, Texas. The effect of low tonicity on chromosomes
was reported long ago by Slifer (1934) who worked on insect embryos.
Hughes (1952), who made systematic studies on the effect of tonicity
on chick cells in vitro, also noticed the phenomenon of chromosome
dispersion under hypotonic osmotic pressure. Not being chromosome
cytologists, neither Slifer nor Hughes capitalized on such important
findings. About the same time, Makino and Nishimura (1952) proposed
a water pretreatment technique for squash preparations of solid tissues, a
method similar to the hypotonic solution pretreatment. Unfortunately,
the effect of hypotonicity cannot reach its maximum when solid tissues
are treated, but cells in vitro respond to tonicity changes to the fullest
extent.
The hypotonic solution technique only marked the beginning of the
revolution in mammalian karyology. Tissue Culture techniques employed during the early 1950's were cumbersome and not entirely
suitable for detailed chromosome examinations. The major improvement was made by Tjio and Levan (1956), who borrowed from plant
cytology the method of colchicine treatment and squash technique.
Colchicine accumulates mitotic figures and also considerably contracts
the chromosomes so that there is less tangling and overlapping of the
chromosomes in the preparations. The squash procedure flattens the
cells and forces chromosomes to lie in one focal plane. Observational
errors are, therefore, minimized.
Currently most laboratories employ one or more of the following
materials for chromosome preparations: (1) cells grown in vitro from
biopsy material, notably skin (Book, Fraccaro and Lindsten, 1959;
Harnden, 1960b; Edwards, 1960; Hsu and Kellogg, 1960; Tjio and
Puck, 1958a); (2) cells from bone marrow, either aspirated and fixed
directly or grown in vitro for a short period of time (Ford, Jacobs and
Lajtha, 1958), and (3) leukocytes from peripheral blood (Hungerford,
Donnelly, Nowell and Beck, 1959; Moorhead, No well, Mellman,
T . G. HSU
characteristic of normal females. Conversely, with Turner's syndrome
(Turner, 1938), the patients should be classified as sexually underdeveloped females. But as far as their sex chromatin is concerned, it is
negative, indistinguishable from normal males. These contradictory
cases found materialistic answers during recent years in the studies
of human chromosomes, as will be shown in the following section.
It is probably not unfair to say that today's booming mammalian
karyology is owing, to some extent, to my salesmanship (Editorial,
1959a) when I proposed the use of a hypotonic solution treatment
to spread the chromosomes of cells in vitro (Hsu and Pomerat, 1953).
This discovery of hypotonic solution treatment was purely accidental
in our laboratory (Hsu, 1952), then at The University of Texas Medical
Branch in Galveston, Texas. The effect of low tonicity on chromosomes
was reported long ago by Slifer (1934) who worked on insect embryos.
Hughes (1952), who made systematic studies on the effect of tonicity
on chick cells in vitro, also noticed the phenomenon of chromosome
dispersion under hypotonic osmotic pressure. Not being chromosome
cytologists, neither Slifer nor Hughes capitalized on such important
findings. About the same time, Makino and Nishimura (1952) proposed
a water pretreatment technique for squash preparations of solid tissues, a
method similar to the hypotonic solution pretreatment. Unfortunately,
the effect of hypotonicity cannot reach its maximum when solid tissues
are treated, but cells in vitro respond to tonicity changes to the fullest
extent.
The hypotonic solution technique only marked the beginning of the
revolution in mammalian karyology. Tissue Culture techniques employed during the early 1950's were cumbersome and not entirely
suitable for detailed chromosome examinations. The major improvement was made by Tjio and Levan (1956), who borrowed from plant
cytology the method of colchicine treatment and squash technique.
Colchicine accumulates mitotic figures and also considerably contracts
the chromosomes so that there is less tangling and overlapping of the
chromosomes in the preparations. The squash procedure flattens the
cells and forces chromosomes to lie in one focal plane. Observational
errors are, therefore, minimized.
Currently most laboratories employ one or more of the following
materials for chromosome preparations: (1) cells grown in vitro from
biopsy material, notably skin (Book, Fraccaro and Lindsten, 1959;
Harnden, 1960b; Edwards, 1960; Hsu and Kellogg, 1960; Tjio and
Puck, 1958a); (2) cells from bone marrow, either aspirated and fixed
directly or grown in vitro for a short period of time (Ford, Jacobs and
Lajtha, 1958), and (3) leukocytes from peripheral blood (Hungerford,
Donnelly, Nowell and Beck, 1959; Moorhead, No well, Mellman,