The Internet
told me that a neutrophil drumstick is a nuclear lobule attached by a slender
strand to the nucleus of some polymorphonuclear leukocytes of normal females
but not of normal males. They contain the Barr body. Barr body...?
"a small, densely staining structure in the
cell nuclei of females, consisting of a condensed, inactive X chromosome. It is
regarded as diagnostic of genetic femaleness"
But
that just raised more questions.
Inactive
X chromosome... Why is any chromosome inactive, X or otherwise. It turns out
that if one of the X chromosomes isn't inactivated in females they will have
twice as many X chromosome gene products as males, who only possess a single
copy of the X chromosome. Obvious really when you think about it.
Apparently
the choice of which X chromosome will be inactivated is random in humans and
all placental mammals (but not in
marsupials… but I digress), but once an X chromosome is inactivated it will
remain inactive throughout the lifetime of the cell and its descendants in the
organism.
This
suggests why you can see, that there are two red cell populations
of erythrocytes: deficient cells and normal cells in the blood of women
heterozygous for Glucose-6-phosphate dehydrogenase (G6PD) deficiency, depending on whether the inactivated X chromosome
(in the nucleus of the red cell's
precursor cell) contains the normal or defective G6PD allele.
However,
sometimes the X-inactivation isn't entirely
random. It can be skewed toward the paternal or maternal X chromosome
This
explains why although X-linked, approximately one third of patients with congenital
sideroblastic anaemia are women due to skewed X-inactivation
One
lives and learns...
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