Identical Twins: Are they really Identical....?

Posted by Tandarin Nike Sunday, November 22, 2009 12:27 AM

Just when we thought we knew everything there is to know about identical twins, comes this new revelation. It now seems that identical twins, previously thought to have 100% genetic resemblance, are anything but identical.

A group of researchers in the west recently studied the genetic make up of 19 pairs of identical twins. They found that there are subtle but clear differences between the DNA of these twin pairs. These variations may be due to differences that occur during genetic copying and to mutations.

In most cases, these slight differences have no observable effect in the physical and developmental make up of the twins. In some cases, however, these variations can make a world of difference health-wise.

Doctors are puzzled how one twin can develop a disorder or disease and the other not. They've always attributed these differences to environmental factors.

In the case of our twin boys, Ankush develops body rash quite often while Alok doesn't. Me and my wife have always asked ourselves, where have we gone wrong? Have we somehow neglected one and favored the other? After all we are responsible for a lot of these so-called environmental factors, from food, to beds, to toys and baby products as they grew up.

It's a relief to know that genetics, something beyond our control, plays a role in all of these.

But now, we are at loss. With this new discovery, the term? Identical twins? Has become a misnomer. Monozygotic would be a more appropriate term but who would understand that? The next time somebody asks us whether our boys are identical, how do we respond?

Over the years, human biology experts cannot agree about the mechanisms of monozygotic twinning. Dizygotic twinning is easy enough to figure out because the two embryos come from two eggs which are separately fertilized by sperms. The reasons for multiple egg production have been linked to hormones, maternal age, and well, the number of embryos transferred during an IVF cycle. Monozygotic twinning however is more of a mystery.

Some experts say it’s something to do with genetics, e.g. “it runs in the family”. Others say it’s the environment.

There is also the question whether producing twins is an advantage at all. Some experts believe that at least 12% of natural conceptions can result in twin embryos. However, in most cases, one embryo doesn’t survive so that only about 2% those pregnancies successfully produce twins. The disappearing twin is a common phenomenon. However, there could possibly be even more cases where one twin is lost before it is even detected.

Whatever the findings, this subject definitely interest us. It might soon even help us in answering one of the most common questions we hear: Which side of the family has twins? Yours or his?

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