Concerns the determination of the gonads. In mammals, determination strictly
chromosomal; not influenced by the environment. Most cases- female = XX; male=
XY Every individual organism has atleast one X Chromosome. Since the female has
2 X chromosomes, each of her eggs posses one X chromosome. The male posses an X
and a Y, so therefore the male can produce 2 kinds of sperm, one with an X
chromosome and one with a Y chromosome. If an offspring receives an X and a Y,
then it will be a male. TheY chromosome carries a gene that encodes a testis
determining factor. If a person had an innumerable number of x chromosomes and
one y chromosome, they would be male. If a person is born with only a single x
chromosome and no second x or y, then they develop as a female, but are
infertile.(not able to maintain ovarian follicles) More Primary Sex
Determination- In the is absence of the Y chromosome , the primordial gonad body
develops into ovaries. the ovary then produces the estrogenic hormones, which
contains estrogen and other such hormones, enabling the development of the
Mullerian duct into the uterus, fallopian tubes, and upper end of the vagina. In
the presence of Y chromosome, the testes form. The testes secrete two major
enzymes. The first hormone, AMH(anti-Mulllerian duct hormone), destroys to
Mullerian duct. The second, testosterone, stimulates the masculinization of the
fetus. During this process the penis, scrotum, and other male anatomical
structures form. The development of the primordial breast is inhibited. The
body, therefore, has the female phenotype unless it is altered by two hormones
created in the fetal testes. The development of gonads is the only fetal organ
development process that has the chance of developing into more than one organ
(under normal circumstances and barring mutations). The primordial gonad can
develop into either an ovary or a testis. Before the gonad develops into the
testes or ovary, it first goes through an indifferent stage, also known as a
bipotential stage, during which time it has neither male or female
characteristics. In humans, the primordial gonad first develops in the 4th week
and remains indifferent until the 7th week. Sex Determinant genes- In humans,
the major genes for the testis determining factor reside on the short arm of the
Y chromosome. Individuals born with the short arm of the Y chromosome, but not
the long are males. Those born with the long end but not the short are actually
female. Through scientific research on XX males and XY females, the position of
the testis-determining gene has been narrowed down to a small region. On the
short arm of the Y chromosome there is believed to be an area called the HMG
box, which stands for high-mobility group box. This HMG box is believed to
contain the genetic information to establish masculinity. There are two known
major genes in this HMG box that are believed to have an effect on the
determining of sex, SRY and SOX9. SRY (sex-determining region of the Y) is found
in XY males, is absent from XX females, is found in the rare XX males, and is
absent in the XY females. Many XY women were found to have a point mutation in
the SRY gene, which would prevent the SRY protein from binding to the DNA. Since
humans are difficult to study, Scientists found a different way to study this
gene. In mice, there is a gene homologous to SRY, which is named Sry. the mouse
gene also correlates with the presence of testes; it is present in XX males and
absent in XY females. To further test this theory of Sry being the testes
determining gene, scientists injected the Sry sequence into XX fertilized mice
zygotes. In most instances the mice developed testes and the rest of the male
accessory organs, but weren’t fertile(the presence of two X chromosomes
prevents sperm formation in both mice and men). This is the majority of the
evidence supporting this gene as the one that determines whether you are male or
female. The function of SOX9 is unclear. If a male is born without a functional
copy of SOX9, then a syndrome called campomelic dysplasia develops. It involves
numerous skeletal and organ systems. If born without SOX9, the male child dies
soon there after from distress arising from defective bronchia and tracheas.
However, 3/4 of those males born without SOX9 phenotypicaly appear to be females
or hermaphrodites. Since SOX9 is on the Y Chromosome, almost all women are born
without it. Secondary sex determination- concerns the bodily phenotype outside
the gonads. Secondary sex determination concerns the development of the female
and male phenotypes form the hormones secreted by the ovaries and testes. In the
absence of gonads, the female phenotype is generated. A male mammal has a penis,
seminal vesicles, a prostate gland, and often sex specific size, vocal
cartilage, and musculature. A female mammal has a vagina, uterus, oviducts,
mammary glands, and often sex specific size, vocal cartilage, and musculature.
(1953- scientist named Jost removed fetal rabbit gonads before they had
differentiated. The rabbits that resulted were all female, regardless if they
had a pair of XX chromosomes, or a pair of XY chromosomes. They were all
infertile, but developed a uterus, a vagina, and fallopian tubes.)
Hermaphrodites are named after the son of Hermes and Aphrodite. Having inherited
the beauty of both parents, he excited the love of the nymph of the Salmacis
fountain. As he bathed in this fountain, she embraced him and prayed to the gods
that they might forever be united. She got her wish. Hermaphroditism in Fishes-
The most common vertebrate hermaphrodite. There are 3 kinds of hermaphrodites in
fish. The first are synchronous hermaphrodites. These have ovaries and testes at
the same time. Fish in this group form spawning pairs. Each fish takes turns
spawning the other fish from the pair’s eggs. The second are protogynous
hermaphrodites. These fish are females at the start of their lives but later
become males. The third group is protandrous hermaphrodites. These fish are
males first, and then become females at the end of their lives.
