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.