Wednesday, January 12, 2011

Facts about Twinning Continued....

So to follow-up to my post yesterday we'll continue on with questions 2-6.

1. Identical vs. Fraternal how they are formed?
2. What types of twins are most common?
3. What sexes of twins are most common?
4. What are the chances of having multiple multiples?
5. Is there a twin gene? Run in families?
6. Do twins skip a generation?

2. What types of twins are most common?

About 2/3 of all twins are fraternal. Leaving only 1/3 of all twins to be identical. This was no surprise since identical twins just HAPPEN to form when an egg split. Pretty much a miracle!

3. What sexes of twins are most common?
About 40% of all twins are fraternal boy/girl twins! Here is the list in order of frequency.

1. fraternal boy/girl

2. fraternal girl/girl

3. fraternal boy/boy

4. identical girl/girl

5. identical boy/boy

Actually one of the most interesting things I read is that the more sets of multiples you have the greater the chances are of having girls! Seems very interesting.

4. What are the chance of having multiple sets of multiples?
As I've stated before the chances of having 2 sets of identical twins are 1 in 70,000. The chance of having 1 set identical and 1 set fraternal is about 1 in 10,000. The chance of having two sets of fraternal twins are 1 in 3,000. This website I found was sooo interesting! There are some super crazy people out there who have LOTS and lots of multiples so to have 2 sets of twins like us doesn't seem like a big deal when looking at all the other statistics!

5. 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 dizgotic (or fraternal) twins. So, in families where the women have a gene for hyperovulation, 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. NOT just the fact of HAVING TWINS! A HUGE misconception when people think about twins!

6. Do twins skip a generation?
If your father was a twin, but you weren't, are you more likely to have twins? It's a common misconception that twins skip a generation in families. There is absolutely no evidence, other than circumstantial, that twins are more likely to occur every other generation. However, if you consider the influence of genetic hyper ovulation, this pattern could appear in families depending on whether their children were sons or daughters.

  • Generation 1: Grandma
    Grandma has the gene for hyperovulation. She & Grandpa have fraternal boy twins, Rob and Bob

  • Generation 2: Rob & Bob
    While Grandma's sons may carry the gene for hyperovulation, they do not ovulate. They will not have twins (excluding other factors). However, they each have a daughter.

  • Generation 3: Molly & Polly
    Molly and Polly, cousins, inherit the gene for hyperovulation from their fathers. They each have a set of twins.

You can see how this example makes it appear that twins skip a generation in families. The pattern is influenced by whether the inheritor of the hyper ovulation gene is male or female.

So that wraps up the questions I've had from people and questions I've had myself. I got most of my research from the Facts About Multiples Encyclopedia here. A VERY interesting site about twins, triplets and higher order multiples (meaning more than 3 babies). If you have any other questions leave them in the comments and I'll be doing another post soon about the benefits of finding out if twins are identical or fraternal (if they are the same sex) other than just for personal knowledge.

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