Chapter 15: Sex (Genome)

•In the Prado Museum in Madrid hangs a pair of paintings by the seventeenth-century court painter Juan Carreno de Miranda, called ‘La Monstrua vestida’ and ‘La Monstrua desnuda’: the monster clothed and the monster naked.

• They show a grossly fat but very unmonstrous five-year-old girl called Eugenia Martinez Vallejo.

• With hindsight, it is plain that she shows all the classic signs of a rare inherited disease called Prader-Willi syndrome, in which children are born floppy and pale-skinned, refuse to suck at the breast but later eat till they almost burst, never apparently experiencing satiety, and so become obese.

• Prader-Willi syndrome was first identified by Swiss doctors in 1956.

• In both Prader-Willi and Angelman’s syndrome it soon became clear that the same chunk of chromosome 15 was missing. The difference was that in Prader-Willi syndrome, the missing chunk was from the paternal chromosome, whereas in Angelman’s syndrome, it was from the maternal.

•David Haig reinterpreted the mammalian placenta as a foetal organ designed to parasitize the maternal blood supply, based on its hormones and effects on the mother’s body.

• This theory predicted that imprinting would not occur in animals that lay eggs, because a cell inside an egg has no means of influencing the investment made by the mother in yolk size.

• Lo and behold, both the IGF2 and the IGF2R genes are imprinted: The first being expressed only from the paternal chromosome, and second from the maternal one.

•If imprinted genes exist only to combat each other, then they can be turned off with no effect on embryo development.

• Elimination of all imprinting leads to normal mice.

• Imprinting is likely not purposeful, and is just another illustration of the theory of the selfish gene and sexual antagonism.

• Paternal maniculatus genes expecting competition in the womb will lead to aggressive maternal maniculatus genes, resulting in a bigger baby if the promiscuous father fathered it.

•Methylation is removed during early development, but somehow imprinted genes escape this process.

• Imprinted genes are what stood between science and the cloning of mammals for many years.

• The imprinted region of chromosome 15 contains about eight genes, one of which is responsible for Angelman syndrome.

• In most cases where an egg has three copies of a chromosome, one copy is deleted at random by the body.

•UBE3A is a gene that is switched on in the brain.

• The symptoms of Prader-Willi and Angelman indicate something unusual about the brains of their victims.

• Other imprinted genes are active in the brain, and it seems that in mice much of the forebrain is built by maternally imprinted genes.

• Paternal cells are comparatively scarce in the brain, but much commoner in the muscles.

•Yoh Iwasa argues that paternal X chromosomes are found only in females and behaviour that is characteristically required of females should be expressed only from paternal chromosomes.

• Skuse and his colleagues located eighty women and girls aged between six and twenty-five who suffered from Turner’s syndrome, a disorder caused by the absence of all or part of the X chromosome.

• The twenty-five girls missing the maternal chromosome were significantly better adjusted than the fifty-five girls missing the paternal chromosome.

• Skuse and his colleagues provided further evidence of this from children who were missing only part of one X chromosome.

• This study has two massive implications: First, it suggests an explanation for the fact that autism, dyslexia, language impairment and other social problems are much commoner in boys than girls; second, it provides evidence for nature having a role to play in gender differences.

•In 1997, Milton Diamond and Keith Sigmundson tracked down Joan, who they found was actually a man.

• John had always felt unhappy as a child and wanted to wear trousers and mix with boys.

• At 14, he learned of the surgery that had been performed on him and stopped taking hormones. He changed his name back to John, resumed living as a man, removed his breasts, married a woman, and adopted her children.

• Held up as an example of socially constructed gender roles at the time, John proved that nature does play a role in gender instead.

YARPP List

Related posts:

1. Law 17: Seize the Historical Moment (The Laws of Human Nature)
2. Part 2: Isolate the Victim (The Art of Seduction)
3. Chapter 16: The Capitalist Creed (Sapiens)
4. On Nietzsche’s Thus Spoke Zarathustra Summary (8.4/10)