12.
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C Y T O L O G Y
403
Battips and Hungerford, 1960; Edwards and Young, 1961). The last
method combined NowelPs findings (1960) that phytohemagglutinin is
a mitogen to monocytic cells and the air-drying technique devised by
Rothfels and Siminovitch (1958) and by Tjio and Puck (1958b). This
method enjoys its great popularity because it yields fast results, and
since it is almost painless, few persons object to donating a small
amount of venous blood (for technical details, cf. the chapter by Lajtha
in Vol. 2). Furthermore, to do only blood culturing, a chromosome
laboratory can be equipped with relatively small cost. However,
because of possibilities of mosaicism, an unequivocal conclusion cannot
always be made from one type of tissue. It is, therefore, preferable to
utilize several different tissues for confirmation.
Little objection will be raised if the paper of Tjio and Levan (1956)
is considered as the advent of human cytogenetics. Using short-term
culture of human tissues, these investigators discovered that the diploid
chromosome number of man is 46, not 48, which had been the standard
number for many years. The photographs of Tjio and Levan are so
superb that they leave no room for doubt, and their findings were
promptly confirmed by Ford and Hamerton (1956) using gonadal
material. Since then a large collection of chromosome investigations
on human subjects has been conducted in various laboratories, and in
all indisputable cases the normal diploid number is 46.
The natural step after the discovery of the correct chromosome
number of man was to determine the karyotype. Several systems of
nomenclature were devised (Ford et al., 1958; Chu and Giles, 1959;
Tjio and Puck, 1958a; Levan and Hsu, 1959). T o reach an agreement
in nomenclature (an idea initiated by C. E. Ford and T. T. Puck) a
group of human chromosome workers met at Denver, Colorado, U.S.A.
to propose a standard system (Human Chromosome Study Group,
1960). In spite of some discontent, the Denver system at least temporarily unified the nomenclature of human chromosomes.
The Denver system is indeed not a perfect one. During the conference
disagreements frequently occurred. Many such disagreements were
resolved by compromise or were reluctantly yielded by one side or
another. Occasionally the decision was reached by resorting to voting.
One objection raised by several members related to the separation
of the X chromosome from a number of submetacentrics of similar size.
Criticisms of this type have been made by Patau (1960). In fact, the
numbering of chromosomes was made as a contingency, not a finality,
for not all chromosome pairs can be unequivocally identified in the
majority of metaphase figures. In the Denver document the descriptions
that chromosome 13 has a long satellite, 14 a short one, and 15 no
satellite, are most likely erroneous because several workers have claimed
G E N E T I C
C Y T O L O G Y
403
Battips and Hungerford, 1960; Edwards and Young, 1961). The last
method combined NowelPs findings (1960) that phytohemagglutinin is
a mitogen to monocytic cells and the air-drying technique devised by
Rothfels and Siminovitch (1958) and by Tjio and Puck (1958b). This
method enjoys its great popularity because it yields fast results, and
since it is almost painless, few persons object to donating a small
amount of venous blood (for technical details, cf. the chapter by Lajtha
in Vol. 2). Furthermore, to do only blood culturing, a chromosome
laboratory can be equipped with relatively small cost. However,
because of possibilities of mosaicism, an unequivocal conclusion cannot
always be made from one type of tissue. It is, therefore, preferable to
utilize several different tissues for confirmation.
Little objection will be raised if the paper of Tjio and Levan (1956)
is considered as the advent of human cytogenetics. Using short-term
culture of human tissues, these investigators discovered that the diploid
chromosome number of man is 46, not 48, which had been the standard
number for many years. The photographs of Tjio and Levan are so
superb that they leave no room for doubt, and their findings were
promptly confirmed by Ford and Hamerton (1956) using gonadal
material. Since then a large collection of chromosome investigations
on human subjects has been conducted in various laboratories, and in
all indisputable cases the normal diploid number is 46.
The natural step after the discovery of the correct chromosome
number of man was to determine the karyotype. Several systems of
nomenclature were devised (Ford et al., 1958; Chu and Giles, 1959;
Tjio and Puck, 1958a; Levan and Hsu, 1959). T o reach an agreement
in nomenclature (an idea initiated by C. E. Ford and T. T. Puck) a
group of human chromosome workers met at Denver, Colorado, U.S.A.
to propose a standard system (Human Chromosome Study Group,
1960). In spite of some discontent, the Denver system at least temporarily unified the nomenclature of human chromosomes.
The Denver system is indeed not a perfect one. During the conference
disagreements frequently occurred. Many such disagreements were
resolved by compromise or were reluctantly yielded by one side or
another. Occasionally the decision was reached by resorting to voting.
One objection raised by several members related to the separation
of the X chromosome from a number of submetacentrics of similar size.
Criticisms of this type have been made by Patau (1960). In fact, the
numbering of chromosomes was made as a contingency, not a finality,
for not all chromosome pairs can be unequivocally identified in the
majority of metaphase figures. In the Denver document the descriptions
that chromosome 13 has a long satellite, 14 a short one, and 15 no
satellite, are most likely erroneous because several workers have claimed