12. G E N E T I C C Y T O L O G Y
451
X in females, without which the individual becomes a sexually underdeveloped female. Before we can probe this problem further, perhaps we
need more information of the behavior of the sex chromosomes in the
gonad and many other tissues. W e do know, however, that the majority
of male somatic cells do not bear sex chromatin, even a tiny one that
is equivalent to the Y chromosome.
Let us assume that the Y chromosome contains male-determining
genes, or male determiners. It is not known, however, whether there
are male determiners in the autosomes. T o interpret the genetic
constitution of intersexes with female karyotype, there appears no
such necessity to assume that a piece of Y is translocated to an autosome. Mutations from female-determiners to male-determiners would
accomplish the same. On the other hand, there have been doubts about
the female-determining factors being located in the X chromosome.
Comments Russell (1961): "It seems improbable, from the available
evidence that the X is strongly female-determining—that is, that female
determiners are preferentially located on the X ; for, if this were the
case, both X O and X X Y should be much more in the direction of
intersexuality than they actually are." In other words, since addition
or deletion of X chromosomes does not grossly alter the sex phenotype,
female determiners are probably not located in the X . Nevertheless, if
we follow the inactivation hypothesis, all individuals, male or female,
normal or pathological, have basically one active X chromosome
(Ohno, 1961). Regardless of the number of X chromosomes present,
X X X or X X X X , additional X elements are largely heteropyknotic.
Thus Russell's argument does not appear to be a strong one, even
though the presence of autosomal female determiners is not an impossibility.
It is rather satisfying to think that human genetics, mammalian
cytology, and related fields have come a long way within a short time
span. Efforts have been started to connect some of the findings with
a molecular approach. The future of genetic cytology is conceivable
dynamic and bright, and it is safe to say that cell cultures will continue
to be favorable experimental material.
A C K N O W L E D G M E N T
Many investigators, notably Drs. Paul S. Moorhead, George
Yerganian, Murray L. Barr, J. Herbert Taylor, Susumu Ohno, and
Gerald C. Mueller, supplied me with original photomicrographs or
permitted me to reproduce some of their published materials, and to
them I express my sincerest thanks.
451
X in females, without which the individual becomes a sexually underdeveloped female. Before we can probe this problem further, perhaps we
need more information of the behavior of the sex chromosomes in the
gonad and many other tissues. W e do know, however, that the majority
of male somatic cells do not bear sex chromatin, even a tiny one that
is equivalent to the Y chromosome.
Let us assume that the Y chromosome contains male-determining
genes, or male determiners. It is not known, however, whether there
are male determiners in the autosomes. T o interpret the genetic
constitution of intersexes with female karyotype, there appears no
such necessity to assume that a piece of Y is translocated to an autosome. Mutations from female-determiners to male-determiners would
accomplish the same. On the other hand, there have been doubts about
the female-determining factors being located in the X chromosome.
Comments Russell (1961): "It seems improbable, from the available
evidence that the X is strongly female-determining—that is, that female
determiners are preferentially located on the X ; for, if this were the
case, both X O and X X Y should be much more in the direction of
intersexuality than they actually are." In other words, since addition
or deletion of X chromosomes does not grossly alter the sex phenotype,
female determiners are probably not located in the X . Nevertheless, if
we follow the inactivation hypothesis, all individuals, male or female,
normal or pathological, have basically one active X chromosome
(Ohno, 1961). Regardless of the number of X chromosomes present,
X X X or X X X X , additional X elements are largely heteropyknotic.
Thus Russell's argument does not appear to be a strong one, even
though the presence of autosomal female determiners is not an impossibility.
It is rather satisfying to think that human genetics, mammalian
cytology, and related fields have come a long way within a short time
span. Efforts have been started to connect some of the findings with
a molecular approach. The future of genetic cytology is conceivable
dynamic and bright, and it is safe to say that cell cultures will continue
to be favorable experimental material.
A C K N O W L E D G M E N T
Many investigators, notably Drs. Paul S. Moorhead, George
Yerganian, Murray L. Barr, J. Herbert Taylor, Susumu Ohno, and
Gerald C. Mueller, supplied me with original photomicrographs or
permitted me to reproduce some of their published materials, and to
them I express my sincerest thanks.