Twin Studies

Welcome!

Twins are a rare, but useful resource when it comes to molecular biology. They can provide useful information about genetics versus environment that can be applied to many different aspects of life.

There are two different kinds of twins; identical and fraternal.

1.) Identical twins come from one egg which is fertilized by one sperm. That single fertilized egg, or zygote, then splits into two separate identical embryos which continue to grow. If the fertilized egg splits more than once triplets, quadruplets, quintuplets etc. will result. If the egg does not split at all then conjoined twins may be the result.

2.) Fraternal twins come from two separate eggs that are ovulated at the same time. In this case the two eggs are fertilized by two different sperm. Fraternal twins are just like an ordinary brother and sister, except that they are born at the same time. They have a different genetic makeup and tend to be very independent of each other.

Twin studies are conducted all over the world, and help to distinguish between what is influenced by genetics and what is influenced by environment. This means that they can determine whether a disorder is something you are born with, or whether it is something that is developed based on the surroundings. Because identical twins have the same genetic makeup and come from the same mother, it can be assumed that any differences between the twins is caused by environmental factors. Fraternal twins have the same pre-birth environment as well, but have different DNA so they tend to have many differences between them.



This diagram illustrates how identical twins are born. If the fertilized egg splits more than once, triplets, quadruplets and quintuplets are the result. If the egg does not split at all conjoined twins are the result.

.Mary-Kate and Ashley Olsen - Famous twins

Although twin studies cannot usually prove the answer to a question, they tend to provide information that may help lead to the answer. Researchers can usually find out whether or not something is based on genetics by seeing if monozygotic twins have the same effects. Infomation such as this may allow researchers to rule out genetics or environment as the cause. If they can figure this out, then they can narrow their research down to just one cause and focus directly on it. Although the ultimate goal of medical studies is to find a cure, information from twin studies has lead researchers to many new discoveries. This includes the prevention and control of many different diseases.

Twin studies are not 100% accurate, therefore research cannot and should not be based strictly on them. Twin studies do however provide very useful information that can be used towards other science studies. They tend to be used along with other research tools for more accurate results.

Key Terms

Monozygotic (Identical Twins): Derived from a single egg.

Dizygotic (Fraternal Twins): Derived from two separately fertilized eggs.

Concordant: Similar with respect to one of more particular characteristics.

Discordant: Dissimilar with respect to one or more particular characteristics.