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The process of meiosis in females occurs during oogenesis, and differs from the typical meiosis in that it features a long period of meiotic arrest known as the dictyate stage and lacks the assistance of centrosomes. [53] [54] In males, meiosis occurs during spermatogenesis in the seminiferous tubules of the testicles.
In the XY sex-determination system, the female-provided ovum contributes an X chromosome and the male-provided sperm contributes either an X chromosome or a Y chromosome, resulting in female (XX) or male (XY) offspring, respectively. Hormone levels in the male parent affect the sex ratio of sperm in humans. [25]
In both males and females, the sex organs consist of two structures: the internal genitalia and the external genitalia. In males, the gonads are the testicles and in females, they are the ovaries . These are the organs that produce gametes (egg and sperm), the reproductive cells that will eventually meet to form the fertilized egg ( zygote ).
After examination, it was discovered that the difference between a typical XX individual (traditional female) and a sex-reversed XX man was that the typical individuals lacked the SRY gene. It is theorized that in sex-reversed XX men, the SRY gets translocated to an X chromosome in the XX pair during meiosis .
W. D. Hamilton gave the following basic explanation in his 1967 paper on "Extraordinary sex ratios", [47] given the condition that males and females cost equal amounts to produce: Suppose male births are less common than female. A newborn male then has better mating prospects than a newborn female, and therefore can expect to have more offspring.
For example, while having an XY format, Xiphophorus nezahualcoyotl and X. milleri also have a second Y chromosome, known as Y', that creates XY' females and YY' males. [16] At least one monotreme, the platypus, presents a particular sex determination scheme that in some ways resembles that of the ZW sex chromosomes of birds and lacks the SRY gene.
The human brain. Differences in male and female brain size are relative to body size. [83] Early research into the differences between male and female brains showed that male brains are, on average, larger than female brains. This research was frequently cited to support the assertion that women are less intelligent than men.
Sexual differentiation is the process of development of the sex differences between males and females from an undifferentiated zygote. [1] [2] Sex determination is often distinct from sex differentiation; sex determination is the designation for the development stage towards either male or female, while sex differentiation is the pathway towards the development of the phenotype.