Transcript document

Genes that Affect Gender
Information from OMIM:
http://www3.ncbi.nlm.nih.gov:80/htbinpost/Omim/dispmim?201710#TEXT
More interesting facts about SRY
The gene contains only 250 base
pairs…. a very small gene.
It probably has a long evolutionary
history, being almost identical to
gene involved in reproduction in
yeast.
A sad story of an XY woman...
“who only discovered the truth after hospital
treatment after a diving accident. She then was
made to live her next twenty years in abject
shame. Her father rushed her into marriage, and
her husband told her openly that he had married
her because she was a freak.”
http://www.gendys.mcmail.com/about/04embry
o/41_xychm.htm
At about the sixth week, in male
embryos, Mullerian Inhibiting Factor
(MIF) prevents development towards
a uterus, womb and ovaries.
At the same time androgens
(male steroid hormones are produced
as the testes begin to be formed.
Steroid hormones, including
androgens, cortisol and estrogens are
made from cholesterol. If any of the
first steps in this process are blocked
by genetic defects, the effect is CAH,
congential adrenal hyperplasia.
Congenital lipoid adrenal
hyperplasia is the most severe
form of congenital adrenal
hyperplasia. Affected individuals
can synthesize no steroid
hormones; hence, all are
phenotypic females with a severe
salt-losing syndrome that is fatal
if not treated in early infancy.
In females, other forms of
adrenal hyperplasia can lead to build
up of “male” steroid hormones and thus
result in the appearance of male
genitalia although these individuals
have ovaries. (female gonads) This can
be treated with surgery and
supplemental hormone therapy.
Androgen Insensitivity Syndrome
XY males with this genetic defect
produce plenty of androgen
hormones but lack androgen receptors
and thus their tissues
cannot respond to the male hormones.
Result: testicular feminization
Up until about the eighth week of
embryo development, it is the gonads
that are developing as a result of
either the presence or absence of SRY
expression. The external genitalia
grow identically for either sex.
The next step in development of
“maleness is expression of an enzyme,
5 alpha reductase, produced in males,
which converts testosterone to
dihydrotestosterone.
The result is that the baby
may be labeled as a girl at birth.
But, at puberty the rise of
testosterone allows development
to proceed towards completion.