Uploaded by Seamus Alaric

The Meaning of Sex

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G-7
Seamus Alaric V. Mascareñas
CEAT
SCIENCE 11 – X
February 13, 2020
A Summary:
The Meaning of Sex: Genes and Gender
Lecture One – Deciphering the Language of Sex
David C. Page
“How is a human embryo’s sex determined?” Page said that the sex of a human
being is first known by looking at its genitalia and differentiating its characteristics from
the other. Humans are born at the 40th week after fertilization and only during the seventh
week that the gonad emerges either a testis or an ovary which determines whether it is a
male or a female. Unluckily, sex determination is not hereditary and does not involve the
mixing of the parent’s sex in order for its offspring to be male or female. Based on
historical evidences, environment is a critical factor for this issue, and such includes the
mother’s diet or the father’s temperature and level of excitement during intercourse.
In the 20th century, a debate arises whether if it is the presence/absence of the Y
chromosome or the presence of two X chromosomes is the sex-determining trait. The
later was accepted in relation to the XXY chromosomes of the female fruit flies in the page
one, volume one of Genetics in 1916. This was accepted since extrapolations in biology
are often valid and be modelled onto human beings. The definition changed when
Turner’s Syndrome and Klinefelter Syndrome gave rise to a XO female and XXY male
which negated that the presence of two X chromosomes is a female. Studies shows that
the SRY gene in the Y chromosome is the sex-determining gene after undergoing a
transgenization of a mouse. During meiosis 1, SRY gene crosses over to the other arm
of a chromatid which is why XX males and XY females are born though both cannot
produce sperm. Until now, hermaphroditism is unsolved in humans which refers to an
individual with both gonads present. In short, SRY gene dictates the path of the bipotential
gonad set in humans to become testis.
The presence of males in nature makes a huge difference in terms of survivability
and diversity of each species. Given a scenario where a species capable of sexual
reproduction of males and females through meiosis and a species capable of asexual
reproduction such as parthenogenesis where only females are involved. The first one
takes a lot of generation to populate but can survive mutations through genetic
recombination of DNA, choosing a healthy pile of genes which is passed to the next
generation. On the other hand, a species undergoing parthenogenesis would easily
propagate its number though its only concern is its survivability since it carries the
mutations arose from each generation. Thus, sex can be beneficial for both genetic
diversity and chromosomal stability of each gene.
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