Silly question time... TWINS

[Tom Tom]

So, if I had children it would have no effect on them, but if it has been passed onto me from my mum who may have had it passed on from her dad. However my children could get it from me and if there were girls then they may have twins which would mean they were the great great grandchildren of my grandad. But if I had boys who then had girls who then had twins they would be my great grandchildren and my grandads great great great grandchildren.

eh 'eck.. I need a lie down. lol

[KiteRunner]

Any of the females COULD have passed the gene onto her son...who may then pass it on to any of his daughters AND any of his sons.

All depends which X chromosome gets selected at each conception.

OC

I think he would have a bit of trouble passing an X on to his son, wouldn't he, OC?!

[Olde Crone Holden]

Kate

Yes, of course, getting my genes mixed up with my chromosomes.

I was thinking about a man passing on his own recombined genes to his son, which would of course be a mixture of the chromosomes of his X and Y genes.

So, as you were - if it is a gene for twins then it comes from the mother's side. Her sons can only be carriers.

OC

[KiteRunner]

Is there definitely a gene for twins that is on the X chromosome, then?

[Olde Crone Holden]

Kate

There is a hyperovulation gene (Jackie's post #4).

Yes, so genetic not chromosomal.

OC

[MarionH]

Having just been through the joy of son and dil having twin girls a few months ago we went through every site on the web (well it felt like it) to find out how this happens (the twin bit!).

One of the sites explained it reasonably well (enough for us to get a grip on it!) - I have posted it below (hope that's OK - it's from a public site)

About.com Twins and Multiples

Is There a "Twin Gene"?
Of the factors that influence multiple birth, there is only one that could be identified as genetic or explained by family history: hyper ovulation. Hyper ovulation is the tendency to release multiple eggs during ovulation, increasing the chances of conceiving dizygotic (or fraternal) twins. So, in families where the women have a gene for hyper ovulation, genetics would sufficiently explain an increased presence of fraternal twins.

However, only women ovulate. So the connection is only valid on the mother's side of the family. While men can carry the gene and pass it on to their daughters, a family history of twins doesn't make them any more likely to have twins themselves.

Fraternal twins "run in families" on the mother's side only, if she inherits the gene for hyper ovulation.

Didn't help us that much though as there is absolutely no history in any of the family of twins anyway! It was just a fluke - no IVF and their first born! Bit of a shock to the system to say the least.

Don't know if that has helped or made it worse for you

Marion

[KiteRunner]

Thanks.

[Olde Crone Holden]

....but further reading has brought me this information:

"The twin gene has now been identified as being present in chromosome 3"

As only chromosome 45 is sex-linked, the other 44 being recombined DNA from both parents, then surely this means a man could pass on this chromosome to either his sons OR his daughters?

The main purpose of this gene appears to be in processing cholesterol and insulin, and the twinning is a side effect, if you like.

Also interesting - this twinning gene appears to offer some protection against malaria, which might account for the high level of twin births in Africa.

(Just been reading about Chimera twins - how fascinating! They are neither identical nor fraternal. They occur when a sperm from two different fathers fertilises the egg, which then develops in an identical twin way, but passes DNA from each father to each twin. Thus these twins share 50% of their mother's DNA, and they each share 25% of their own father's DNA, and the DNA of the other father! They are very rare - only three recorded sets, but the scientists say these only came to light because of DNA paternity tests and there may be many more)

OC

[KiteRunner]

Wow, I've never heard of that before, OC. There are also supposed to be semi-identical twins, where one egg splits in two and each of the new eggs is fertilised by a different sperm, so the DNA that comes from the mother is identical but that from the father is different. I don't think much research has been done to find out how common or rare this is yet.

[Olde Crone Holden]

Kate

Yes, chimera twins are a subset of the ones you describe.

There is yet another subset, also rare (as far as science has discovered of course) where the two fathers of such twins, each have a faulty gene (XXY) but the fertilisation process recognises this as a mistake and drops either the extra X, or the Y.

If only one father is involved, and has the faulty gene which corrects itself, then you can have identical twins, one of whom is a girl, the other a boy!

(Cor, geneticists must have a permanent migraine!)

Professor Brian Sykes, who I much admire, is adamant that twinning is a serious mistake of nature, one which threatened the survival of the species thousands of years ago, and that all cultures routinely killed the smaller twin at birth.

His reasoning is a bit weak and I am not sure I swallow this! Surely a successful twin pregnancy is a triumph of the genes, ensuring that they have two chances of survival.

OC

[karensainsbury]

I'm fascinated by all this info - I'd never heard of chimera twins!

I have boy/girl twins so read extensively on the subject when I was pregnant (they're now 10).

I understood that the gene needed to have non-identical twins was only passed down the female line, as you say. In fact the last one to have them before me was my great-grandmother. I have been unable to find any twins further back so far, tho.

Apparently, if you carry this gene, you are most likely to have twins near the menopause as the body hurls out extra eggs - whether in a last ditch attempt to reproduce or just getting rid of excess baggage, I don't know! I was actually 37 when I had my twins.

[Boudicca]

I'm fascinated by this subject as multiple births run in my family too. My mother is a twin (her mum was 40 at the time) My grandmother also had an earlier set of twins and some triplets. I recently discovered that my grandmother was a twin and I believe her mother may have had another set of twins as well. Amazingly none of my mum's seven sisters who made it to adulthood had twins and none of their kids either.

[Merry Monty Montgomery]

I suppose when examining our family histories, it may not always be recognised when someone had a multiple birth. The mortality rate would have been higher with smaller babies and if they were stillborn then there would be no record at all.

Imagine not knowing you were having twins until the delivery? Quite a shock!!

[Olde Crone Holden]

Merry

A friend of mine didn't even know she was pregnant and gave birth to twins on the bathroom floor at home!

To make it worse...she already had a 21 year old son, so knew what the symptoms of pregnancy were. Her GP said her symptoms were due to the menopause.

OC

[Merry Monty Montgomery]

*worries that a symptom of the menopause is giving birth to twins on the bathroom floor*

[Olde Crone Holden]

LOL Merry!

Funny thing was, I saw her about three weeks before she gave birth and she didn't look pregnant to me!

OC

[karensainsbury]

I must say there was no danger of anyone not knowing I was expecting twins. By the time I gave birth I looked at least 15 months pregnant!

[Olde Crone Holden]

Here is another useless bit of twin info!

Did you know that left-handed people are now believed to be the survivors of a mirror-image twin pregnancy?

OC

[karensainsbury]

Blimey - one of my twins is left-handed. Don't tell me I started off with 3!

[Olde Crone Holden]

Karen

If one of your twins is left handed and the other one right handed, then they are mirror-image twins (if they are identical, that is)

OC