Sex X and one Y chromosome (XY). The Formation

Sex Determination in Humans is
influenced by genetic and environmental factors. Chromosomal sex is determined
at fertilization. Females generally contain two X chromosomes and no Y
chromosome (XX). While males generally contain one X and one Y chromosome (XY).
The Formation of male or female reproductive structures depends on several
factors such as, gene action, interactions within the embryo, and interactions with the maternal
environment.

The main goal of Sex Differentiation is
to determine the gonadal sex of the embryo. “At 7 weeks, developmental pathways
activate different sets of genes and cause undifferentiated gonads to develop
as testes or ovaries. In early embryos, there are two internal duct systems the
Wolffian duct (male), and the Mu?llerian duct (female)”.

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Males having an X and
a Y chromosome, contain the sex determining gene to develop testis. The main Sex
determining gene is the sex determining region called the SRY gene, found on the Y Chromosome. There are other genes on the
autosomes that also play important roles. Once testes develop they secrete two
hormones testosterone and the Mu?llerian Inhibiting Hormone (MIH). Females
Develop in the Absence of the Y chromosome, they only contain two X
chromosomes. So, they do not contain the Y chromosome with the sex determining
region. The embryonic gonads develop into ovaries and the Wolffian duct system
degenerates while the Mu?llerian
duct system develops to form the oviduct, uterus and parts of the vagina.

The Process of Sex determination is as
follows:

·        
Male:

“Starting with an Egg containing a X sex chromosome, it is fertilized by sperm with Y chromosome, the genetic
sex is an embryo containing X and Y sex chromosomes. The gonadal sex forms
because of the sex-determining region on the Y chromosome (SRY). Bringing about
the development of undifferentiated gonads and testes. Testes secrete
masculinizing hormones, including testosterone, a potent androgen. The Phenotypic
sex is determined because of the presence of testicular hormones, causing the undifferentiated
reproductive tract and external genitalia to develop along male lines” (Cummings).

·        
Female:

“Starting
with an Egg containing a X sex chromosome, it is fertilized by sperm with X
chromosome, the genetic sex
is an embryo containing two X sex
chromosomes. The gonadal sex forms because there’s no Y chromosome, so no SRY.
With no masculinizing influence, undifferentiated gonads develop into ovaries.
There because there are no masculinizing hormones, so the undifferentiated
reproductive tract and external genitalia develop along female lines” (Cummings).

Also, “females are mosaics for
X-linked genes, some cells express the maternal X and others express the
paternal X. For example: cats heterozygous for orange and black genes must
carry two X chromosomes, and that is genetically why calico cats are always
female. They carry both genes containing one orange and one black on each X
chromosome” (Cummings).

The only thing that could disrupt or
alter the phenotypic sex is a Mutation. There are three mutations specifically
that alter phenotypic sex. One is hermaphrodites,
which have both male and female gonads. Another is androgen insensitivity, which is where XY
males become phenotypic females. And lastly pseudo-hermaphroditism, which is where XY males at birth are
phenotypically female and then at puberty develop a male phenotype.

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