D E V E L O P M E N T S I N S E X U A L O R G A N O G E N E S I S
305
However, perhaps there is a more complex interpretation of the freemartin effect. Wislocki (1939), then Schultz (1948), showed that in the
Hapalidae (marmoset), twins normally occur. Wislocki demonstrated that
there were vascular connections between the placentae, such as were
observed between the heterosexual twins of cattle. But no freemartin effect
has been seen in dizygotic, heterosexual marmosets.
In the Hapalidae, males and adult females have an X X / X Y mosaic
structure, as shown in bone marrow and in testis (Benirschke et al., 1962;
Benirschke and Brownhill, 1962, 1963). This fact confirms the existence of
vascular exchange during fetal life. On the other hand, in the freemartin
of Bovidae (2n = 60 chromosomes), Ohno et al. (1962) have shown that
in the testis of the male many mitoses of the XX type occur. This fact is
confirmed by Makino et al. (1965) who studied 13 heterosexual pairs of
cattle that showed the freemartin effect. They demonstrated the X X / X Y
constitution, in both male co-twin and female (freemartin) on cells in
culture, which indicates that each co-twin is actually a chimera. The mosaic
character occurs in mesodermal derivatives (blood, bone marrow, kidney,
lung) but has not been observed in ectodermal structures. In a heterosexual
pair with the female normal, she was always of XX type.
The ratio of X X / X Y components estimated among the total number of
mitoses observed is interesting. For example, in one pair of heterosexual
twins, the blood showed an X X / X Y ratio of 98/13 in the male, and 98/13
in the female. In another case, the female freemartin had 7XX/232XY in
the culture of blood cells and 2XX/48XY in the bone marrow culture.
These phenomena have led Fechheimer et al. (1964) to note that, if
freemartins and their male co-twins were in fact chimeric organisms
(XX/XY), it could be considered that the freemartin condition was linked
directly to the mosaic character of the sex chromosomes. The question
calls for new studies, and it is premature, at the present time, to draw
conclusions on the interpretation of the freemartin, based on the facts that
recent cytogenetic observations are able to demonstrate.
In sum, it appears reasonable to retain Lillie's hormonal interpretation
(1917) as the basic explanation. However it is appropriate to note that, in
the freemartin, three kinds of phenomena occur: (a) transference of a
hormone from the male co-twin to the female co-twin; (b) serological effects
produced by the mixing of the blood (Owen, 1945; Billingham et al., 1952),
resulting in immunological tolerance; and (c) possible effects of the mosaic
constitution of the karyotype (XX/XY). The role of each of these factors
and their possible interaction remain to be determined.
E. Nature of the Initial Reactions in the Differentiation of the Gonads
In the analysis of the mechanisms controlling sexual differentiation of
the gonads, the nature of the biochemical mediators brought into play
305
However, perhaps there is a more complex interpretation of the freemartin effect. Wislocki (1939), then Schultz (1948), showed that in the
Hapalidae (marmoset), twins normally occur. Wislocki demonstrated that
there were vascular connections between the placentae, such as were
observed between the heterosexual twins of cattle. But no freemartin effect
has been seen in dizygotic, heterosexual marmosets.
In the Hapalidae, males and adult females have an X X / X Y mosaic
structure, as shown in bone marrow and in testis (Benirschke et al., 1962;
Benirschke and Brownhill, 1962, 1963). This fact confirms the existence of
vascular exchange during fetal life. On the other hand, in the freemartin
of Bovidae (2n = 60 chromosomes), Ohno et al. (1962) have shown that
in the testis of the male many mitoses of the XX type occur. This fact is
confirmed by Makino et al. (1965) who studied 13 heterosexual pairs of
cattle that showed the freemartin effect. They demonstrated the X X / X Y
constitution, in both male co-twin and female (freemartin) on cells in
culture, which indicates that each co-twin is actually a chimera. The mosaic
character occurs in mesodermal derivatives (blood, bone marrow, kidney,
lung) but has not been observed in ectodermal structures. In a heterosexual
pair with the female normal, she was always of XX type.
The ratio of X X / X Y components estimated among the total number of
mitoses observed is interesting. For example, in one pair of heterosexual
twins, the blood showed an X X / X Y ratio of 98/13 in the male, and 98/13
in the female. In another case, the female freemartin had 7XX/232XY in
the culture of blood cells and 2XX/48XY in the bone marrow culture.
These phenomena have led Fechheimer et al. (1964) to note that, if
freemartins and their male co-twins were in fact chimeric organisms
(XX/XY), it could be considered that the freemartin condition was linked
directly to the mosaic character of the sex chromosomes. The question
calls for new studies, and it is premature, at the present time, to draw
conclusions on the interpretation of the freemartin, based on the facts that
recent cytogenetic observations are able to demonstrate.
In sum, it appears reasonable to retain Lillie's hormonal interpretation
(1917) as the basic explanation. However it is appropriate to note that, in
the freemartin, three kinds of phenomena occur: (a) transference of a
hormone from the male co-twin to the female co-twin; (b) serological effects
produced by the mixing of the blood (Owen, 1945; Billingham et al., 1952),
resulting in immunological tolerance; and (c) possible effects of the mosaic
constitution of the karyotype (XX/XY). The role of each of these factors
and their possible interaction remain to be determined.
E. Nature of the Initial Reactions in the Differentiation of the Gonads
In the analysis of the mechanisms controlling sexual differentiation of
the gonads, the nature of the biochemical mediators brought into play