Sex


 * "All women become like their mothers. That is their tragedy. No man does. That is his." ~Oscar Wilde, //The Importance of Being Earnest//**


 * Genomic Imprinting:**

Sex has much to do with genetic disorders. Not simply sex-linked traits resulting in disorders including Duchenne's Muscular Dystrophy, colorblindness, and Hemophilia, but which chromosome is inherited from which parent has a great impact on the manifestation of a genetic disorder. Such disorders including Prader-Willi Syndrome and Angelman Syndrome, both of which are due to a missing chunk of Chromosome 15, yet are two entirely different disorders because of genomic imprinting. Imprinting is a phenomenon in which expression of an allele in offspring depends on whether it was inherited from the male or female parent.

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 * Prader-Willi Syndrome:**

When a chromosomal deletion from the male parent's chromosome 15 occurs, the patient suffers from Prader-Willi Syndrome. The disorder is prevalent in both boys and girls, and the symptoms associated with the disorder include mental retardation, obesity due to insatiable appetite, hypogonadism, and hypotonia (poor muscle tone). According to Ridley, "In one case, the parent of a Prader-Willi child found the child had consumed a pound of raw bacon in the back of a car while being driven back from the shop. People with this syndrome have small hands a feet, underdeveloped sex organs and they are also mildly mentally retarded" (207). Below are two images: first, a diagram of the deletion that occurs in Prader-Willi, and second, two famous paintings titled "La monstrua vestida" and "La monstrua desnuda," depicting a five-year old girl with Prader-Willi. The video below from the Mayo Clinic provides an in-depth discussion of the manifestation of the disorder and treatments.



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 * Angelman Syndrome:**

Whereas Prader-Willi Syndrome is paternally derived, Angelman Syndrome is the result of the same deletion on chromosome 15 contributed by the mother. As described by Ridley, "In contrast to those with Prader-Willi Syndrome, they are not floppy, but taut They are thin, hyperactive, insomniac, small-headed and long-jawed, and often stick out their large tongues. They move jerkily, like puppets, but have a happy disposition; they are perpetually smiling and are given to frequent paroxysms of laughter. But they never learn to speak and are severely mentally retarded" (207). Despite the deletion occurring in the same section of chromosome 15, the disorder and its symptoms contrast one another greatly depending on which parent contributed the mutated gene. The picture below illustrates the mutated chromosome and depicts two children, one with Prader-Willi contrasted alongside one with Angelman.



**Pronuclear transplantation:** Imprinted genes were studied further in depth when scientists artificially created two embryos: one fertilized egg created with two mothers, and one created with two fathers. Ridley describes the process as "When an egg has been fertilized by a sperm, the sperm nucleus containing the chromosomes enters the egg but does not at first fuse with the egg nucleus: the two nuclei are known as "pronuclei." A clever scientist can sneak in with his pipette and suck out the sperm pronucleus, replacing it with the egg pronucleus from another egg - and vice versa. The is two viable eggs, but one with, genetically speaking, two fathers and no mother and the other with two mothers and no father" (208). However, Ridley later states that both embryos failed to develop properly. The reason for their improper development is that maternally imprinted genes and paternally imprinted genes must work in cooperation for the proper development of a fetus. In a zygote produced by two mothers, the embryo develops well, but the placenta fails to develop and thus the embryo dies. In contrast, in the zygote produced by two fathers, the placenta develops but the embryo does not. Why does this occur?

**Parent-offspring conflict:** Famed biologist David Haig developed the concept of the parent-offspring conflict in regards to genetics. He hypothesized that the reason that a two-mother zygote and a two-father zygote could not develop was because the relationship between the maternal and paternal genes allowed for a balance of fetal and placental development. He suggests that the maternal genes are primarily involved in developing the fetus. However, since the mother's body has to sacrifice both space and nutrients to the fetus, the maternal genes do not create an adequately invasive placenta because, anthropomorphically, the mother's genes are looking out for her own self-interest. Meanwhile, although the paternal genes do not greatly contribute to fetal development, in order to look out for the male's self-interest of passing on its genes, the paternal genes work to create a sufficiently invasive placenta. **Imprinted genes and gender:** Recent studies suggest that imprinted genes may have a role in gender-identification, in that the contributions made to brain development by maternal or paternal genes may result in the offspring's identification to a particular sex. A famous case of nature v. nurture depicts David Reimer, who, as a baby, was castrated in a botched circumcision. His parents chose to raise him as a girl, yet between the age of 9-11 he realized that he did not identify with the female gender and chose to live as a man for the rest of his life, thus suggesting that social norms regarding gender do not necessarily assign a person to a gender, but rather, genetics play a far bigger role: **"The brain is an organ with innate gender. The evidence from the genome, from imprinted genes and genes for sex-linked behaviours, now points to the same conclusion" (218).**