Child is a Father of man but which decides whether
child becomes man or woman.We are
providing here some interesting
facts about how biological activities
determine the fetus future.
The normal human fetus of
either sex has the potential to develop either male or female organs, depending
on genetic and hormonal influences
Every fetus contains structures that are capable of developing into either male or female genitalia, and, regardless of the complement of sex chromosomes, all developing embryos become feminized unless masculinizing influences come into play at key times during gestation.
Most mammals, including humans, have an XY sex-determination system: the Y chromosome carries factors responsible for triggering male development. In the absence of a Y chromosome, the fetus will undergo female development. This is because of the presence of the sex-determining region of the Y chromosome, also known as the SRY gene. Thus, male mammals typically have
an X and a Y chromosome (XY), while female mammals typically have two X chromosomes (XX).
In humans, biological sex is determined by five factors present at birth: the
presence or absence of a Y chromosome, the type of gonads, the sex hormones,
the internal genitalia (such as the uterus in
females), and the external genitalia.
Chromosomal sex is determined at the time
of fertilization; a chromosome from
the sperm cell, either X or Y,
fuses with the X chromosome in the egg cell. Gonadal sex refers to
the gonads, that is the testis or ovaries, depending on which genes are
expressed. Phenotypic sex refers to the structures of the external and
internal genitalia.
A human fetus does not
develop its external sexual organs until seven weeks after fertilization. The
fetus appears to be sexually indifferent, looking neither like a male or a
female. Over the next five weeks, the fetus begins producing hormones that
cause its sex organs to grow into either male or female organs. This process is
called sexual differentiation.
As we know In humans, each egg contains 23 chromosomes, of which 22 are autosomes and 1 is
a female sex chromosome (the X chromosome). Each sperm also contains 23 chromosomes:
22 autosomes and either one female sex chromosome male sex chromosome (or one the Y chromosome).
Two precursor organs
exist in the fetus: the Wolffian duct,
which differentiates into
the structures of the male genital tract, and the Müllerian
duct, the source of the female reproductive organs. During the third
month of fetal development, the Sertoli cells of the testes of XY fetuses begin
to secrete a substance called Müllerian inhibiting hormone.
This causes the Müllerian ducts to atrophy instead of develop into the oviducts
(fallopian tubes)
and uterus. In
addition, the Wolffian ducts are stimulated by testosterone to eventually develop into the
spermatic ducts (ductus
deferens), ejaculatory ducts, and seminal vesicles. If the
fetal gonads do not secrete testosterone at the proper time, the genitalia
develop in the female direction
Males become externally distinct
between 8 and 12 weeks, as androgens enlarge the phallus and cause the
urogenital groove and sinus to fuse in the midline, producing an
unambiguous penis with
a phallic urethra, and a thinned, rugated scrotum.
Dihydrotestosterone will differentiate the remaining male characteristics of
the external genitalia.
A sufficient amount of any androgen
can cause external masculinization. The most potent is dihydrotestosterone (DHT), generated from
testosterone in skin and genital tissue by the action of 5α-reductase. A male
fetus may be incompletely masculinized if this enzyme is deficient.
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