Un-Methylated Spirits

Our 'nurtured' genes determine who we are. Our DNA gene codes for an RNA message that gets printed out into a string of protein that gets folded up in three dimensions to become a little bit of bio-nano-technology. This is why we are tall or short, fat or thin, blue-eyed or brown.

You would think that it would not matter if a chromosome comes from your mother or your father- that there would be no way to tell- after all they simply consist of chunks of DNA. Female mice have 2 copies of their X chromosome- but it is ALWAYS the paternal X that is switched off. This 'tagging' is known as genetic imprinting- and the trick is performed using methylation.

There are 2 "epigenetic" syndromes that are essentially the reverse of each other- both are due to problems with genes on an area of chromosome 15.

Prader-Wili syndrome occurs when neither segment has paternal imprinting- (e.g. the mother's contribution is present, but the father's has been deleted). These children are characteristically obese, hypogonadal and have some intellectual impairment- although interestingly tend to be very good at jigsaw puzzles!

Angelman's Syndrome occurs, by contrast when there is no maternal imprinting present (e.g. the father's contribution is present, but the mother's has been deleted). These children were initially described as "Happy Puppets". They are often affectionate, verbose, and crave human contact.

But there is more. Genes can be tagged "maternal" or "paternal"- but methylation occurs for many other reasons too. A diet high in "methylation" precursors in rats can change the expression of a lot of genes.

Here is the REALLY interesting bit: If methylation occurs in the cells destined to become the sperm or ova- then these traits become hereditary- at least for a few generations. In other words, this represents a form of "Lamarckian" (vs Darwinian) evolution- the inheritance of acquired characteristics.

Offspring of female rats fed folic acid had brown fur due to methylation of the Agouti gene. Offspring of rats who were not fed the supplements had yellow fur- AND a tendency to diabetes and obesity!

You are not what you eat- you are what your mother ate! It makes me wonder- what if the folate supplement that reduces the incidence of neural tube defects and leukemia in our children has more sinister late methylation effects?

What would a genetically normal but completely un-methylated human look like?

Detailed article here, New York Times article here.

Genetics of Homosexuality

Homosexuality is not a disease, not evil, not morally wrong etc etc. What between 2 - 5 buffed people do in the comfort of their designer bedrooms (or in a public cubicle) is their own business. 'All power to them' i say.

On this point, i think the Catholic church has been 'barking up the wrong tree' for quite a while.

The practise of 'sodomy' is considered evil- and that would mean the Church should be targeting heterosexual couples to encourage them to have sex that is:

a) strictly peno-vaginal
b) non-contraceptified
c) done with the lights off

The church should, however, get their own house in order before criticising others. A few years ago the Portland diocese in Oregon decided to cure 'moral bankruptcy' with 'financial bankruptcy'- to avoid paying out too much in damages to victims of institutionalized paedophillia. Does anyone think this is not going on elsewhere? (saw a short for this film recently: "Deliver Us from Evil"- but don't think i'll be rushing to the megaplex to see it soon).

2. The scientific evidence overwhelmingly suggests human sexual orientation is 'given', rather than chosen. Among identical twin boys, if one is gay, the other has a 50 percent chance of also being gay. Among fraternal twins, who do not share the same DNA, there is only a 20 percent chance. The lack of 100% concordance between identical twins is probably the result of methylation of stretches of DNA.

3. There is almost certainly not a single gene that causes homosexuality- but like height or musical ability it is probably polygenic. It is also possible that it is related to fetal exposure to maternal hormonal changes etc- i.e. congenital but not truly 'genetic'.. (unless you consider the genes of the mother).

Homosexuality, however, does require an explanation. How could a series of genes that cause attraction to the same sex (and therefore be unlikely to be passed on) survive thousands/ millions of years of human evolution?

One idea is to compare it to cystic fibrosis- this disease is one of the most common recessive disorders (both carrier parents must have a copy of the gene for heir kids to have a 1:4 chance of the disease). This disease blocks a chloride channel, causing lung secretions to become sticky. The carriers of this gene are, however, perfectly healthy... AND may be protected against severe cases of cholera induced diarrhoea/dehydration.

As the saying goes: "Too much of a good thing..." is .. not a good ..thing. (Strange how that phrase seems to be just the front end and just sort of peters out .... )

So- what sort of advantage (in terms of getting laid) do a few gay genes give you? One idea is that they make males more communicative, flirty and attractive to women. Witness the rise of the metrosexual.. but really.. do women really go for guys with lip liner and eye shadow? Maybe EMO-chicks.

Another idea (New Scientist) is that the mothers of gay boys have a higher fecundity than other mothers (2.7 babies vs 2.4 babies on average in italy). So maybe the genes code for horniness in women (or heightened attraction to men)- and that a gay son who won't give you any grand-bambino's is worth the effort from the genetic point of view. I can't really understand this conclusion ... as i would have thought the number of children would have to be >3.4 to even the odds.

This same research found increased fertility rates ONLY ON THE MATERNAL SIDE. This suggests either a) genes on the X chromosome are at least partly responsible, or b) it's inherited thru mitochondrial DNA. Some researchers claim to have pinpointed a locus on the X chromosome Xq28 - though others have refuted this.

Perhaps the association is 'causative' in the other direction- i.e. families with lots of boys are more likely to have a gay son. This is known as the ominously labelled "Big Brother Effect"- and it has been shown that this is a biological effect- not an environmental one. In other words, it doesn't matter how many brothers you were brought up with (e.g. if you were adopted), but home many older male siblings you have.

None of the research seems to look at the genetics of Lesbianism... although i'm wondering if lesbian cave-women really had much of a choice anyway before being 'knucked' on the head.