2. 1. The X and Y chromosomes are
the sex chromosomes in humans.
Women have two X chromosomes
(XX), while men have one X
chromosome and one Y
chromosome (XY).
2. The presence or absence of the Y
chromosome determines the
individual's sex.
3. During the development of the embryo, if the
sperm fertilizes the egg with an X
chromosome, the resulting zygote will be XX
and will develop into a female. If the sperm
fertilizes the egg with a Y chromosome, the
resulting zygote will be XY and will develop
into a male.
4. During embryonic development, the presence
of a Y chromosome triggers the development
of testes in males, which in turn produce
testosterone, a hormone that is responsible
for the development of male secondary
sexual characteristics.
5. In the absence of a Y chromosome, the
embryo will develop into a female, and the
ovaries will develop, which produce estrogen
and progesterone, hormones responsible for
the development of female secondary sexual
characteristics.
6. Female- Default development. Mesonephric duct
degenerates and Paramesonephric duct develops.
Male
SRY gene on Y chromosome—produces testis-
determining factor testes. Sertoli cells secrete
Mullerian inhibitory factor (MIF, also called
antimullerian hormone) that suppresses
development of paramesonephric ducts.
Leydig cells secrete androgens that stimulate
development of mesonephric ducts.
7.
8.
9. Develops into male internal structures (except
prostate)—Seminal vesicles, Epididymis,
Ejaculatory duct, Ductus deferens
10. Develops into female internal structures—
fallopian tubes, uterus, proximal vagina
(distal vagina from urogenital sinus). Male
remnant is appendix testis.
11. 1º amenorrhea with absent uterus, blind
vaginal pouch, normal female external
genitalia and 2° sexual characteristics
(functional ovaries). Associated with urinary
tract anomalies (eg, renal agenesias)
12.
13. Early in embryonic development in females,
one of the two X chromosomes is randomly
and permanently inactivated in cells other
than egg cells. This phenomenon is called X-
inactivation or lyonization. X-
inactivation ensures that females, like males,
have one functional copy of the X
chromosome in each body cell.
