414
T . G. HSU
cytologically, detailed recording and analysis, based upon a very large
number of cases, should be carried out so that conclusions can be
statistically sound. Probably investigators working on similar problems
should be coordinated in a joint effort to get the most out of each
laboratory. In fact, such a trend has already started. Twelve authors
(Maclean, Mitchell, Harnden, Williams, Jacobs, Buckton, Baikie,
Court Brown, McBride, Strong, Close and Jones, 1962) have made a
joint report on sex chromatin anomalies. If concerted research can
be initiated, one may eventually be able to obtain a good picture of
such problems as the frequency of translocation between, say, the
D chromosomes and 21 in mongolism, as well as the frequency of nondisjunction of chromosomes 21. Another example of comprehensive
analysis was presented by Jacobs et al. (1961) on primary amenorrhea.
Stewart (1961) utilized the data of Jacobs et al. to postulate the possibilities of mapping some genes on the X chromosome.
Since it is well known that half of the gametes are genetically unbalanced in translocation heterozygotes, couples with repeated abortions
should be investigated for possibilities of reciprocal translocation. It
is of great interest to learn that Schmid (1962) did find such a case
among eight families analyzed. It must be borne in mind that a number
of reciprocal translocations would not be detected by this method, and
partial infertility can also be attributed to inversions with crossovers,
to homozygous lethals, and to physiological defects. But this type of
inquiry could be quite valuable in solving some of the puzzling obstetrical problems. The time is probably also ripe for launching a largescale and thorough analysis of the chromosomes of normal persons
to detect hidden abnormalities.
Karyologically, the most important task is to differentiate human
chromosomes more satisfactorily. At present, even identification of the
X chromosome is a rather subjective selection. I agree that it is true,
as expressed by some cytologists, that eye determinations are sometimes
more accurate than meticulous measurements. I do not think that
measurements of total chromosome length or arm ratio would provide
a better answer. Nevertheless, eye determination requires intuition as
well as experience, and these are not possessed by every person.
There is a possibility that some of the difficult chromosomes can be
identified by the presence and localities of secondary constrictions
(De la Chapelle, 1961). Perhaps it will be possible to employ, in the
future, special methods and/or agents to enhance the differences among
chromosomes. For example, a thymidine analogue, 5-bromodeoxyuridine (BUDR), is known to exaggerate secondary constrictions in
Chinese hamster cells (Hsu and Somers, 1961). An antibiotic, mitomycin C, did the same with chromosomes of Vicia faba (Merz, 1961).
T . G. HSU
cytologically, detailed recording and analysis, based upon a very large
number of cases, should be carried out so that conclusions can be
statistically sound. Probably investigators working on similar problems
should be coordinated in a joint effort to get the most out of each
laboratory. In fact, such a trend has already started. Twelve authors
(Maclean, Mitchell, Harnden, Williams, Jacobs, Buckton, Baikie,
Court Brown, McBride, Strong, Close and Jones, 1962) have made a
joint report on sex chromatin anomalies. If concerted research can
be initiated, one may eventually be able to obtain a good picture of
such problems as the frequency of translocation between, say, the
D chromosomes and 21 in mongolism, as well as the frequency of nondisjunction of chromosomes 21. Another example of comprehensive
analysis was presented by Jacobs et al. (1961) on primary amenorrhea.
Stewart (1961) utilized the data of Jacobs et al. to postulate the possibilities of mapping some genes on the X chromosome.
Since it is well known that half of the gametes are genetically unbalanced in translocation heterozygotes, couples with repeated abortions
should be investigated for possibilities of reciprocal translocation. It
is of great interest to learn that Schmid (1962) did find such a case
among eight families analyzed. It must be borne in mind that a number
of reciprocal translocations would not be detected by this method, and
partial infertility can also be attributed to inversions with crossovers,
to homozygous lethals, and to physiological defects. But this type of
inquiry could be quite valuable in solving some of the puzzling obstetrical problems. The time is probably also ripe for launching a largescale and thorough analysis of the chromosomes of normal persons
to detect hidden abnormalities.
Karyologically, the most important task is to differentiate human
chromosomes more satisfactorily. At present, even identification of the
X chromosome is a rather subjective selection. I agree that it is true,
as expressed by some cytologists, that eye determinations are sometimes
more accurate than meticulous measurements. I do not think that
measurements of total chromosome length or arm ratio would provide
a better answer. Nevertheless, eye determination requires intuition as
well as experience, and these are not possessed by every person.
There is a possibility that some of the difficult chromosomes can be
identified by the presence and localities of secondary constrictions
(De la Chapelle, 1961). Perhaps it will be possible to employ, in the
future, special methods and/or agents to enhance the differences among
chromosomes. For example, a thymidine analogue, 5-bromodeoxyuridine (BUDR), is known to exaggerate secondary constrictions in
Chinese hamster cells (Hsu and Somers, 1961). An antibiotic, mitomycin C, did the same with chromosomes of Vicia faba (Merz, 1961).