males are heterogametic
Dosage compensation is achieved by inactivation at random of one
of the two X chromosomes.
The heterochromatized X
chromosome appears as a darkly-staining bodies attached
to the nuclear membrane. The phenomenon was first described in
cats by Dr Murray L. Barr, a Canadian cytogeneticist, and
heterochromatin bodies are now called Barr Bodies. [The other dark bodies within the
nucleus are nucleoli,
which represent repetitive rDNA
testing was introduced in the 1966 Olympic games, in an
effort to detect male athletes supposedly trying to "pass"
as females to gain a competitive advantage. Teams from eastern
Europe were particularly suspect. Such
allegations had been made for many years, and a number of athletes
were stripped of their medals as a result of ambiguous
sex. Barr Body testing never detected deliberate fakery. It
did however detect a number of cases of testicular
feminization syndrome (TFS),
a genetic condition in which an XY
(male) zygote develops as a phenotypically female adult,
due to failure of androgen receptors. Such individuals would test
positive for the presence of a Barr body. In most if not all
cases, the athletes were themselves unaware of their condition.
Figure after M. Barr (1963) by SM
Carr; all text material © 2015 by Steven M.