Dizygotic Twins

Fertilization is a wonderful science, which keeps surprising the research that is being carried out on it. One such example of this is the formation of twins, which is when there is fertilization of eggs in the mother's womb either by one sperm or two sperms. This results in the formation of two offspring at one time and their development is parallel to each other. There are mainly two types of twins viz; identical or monozygotic twins and fraternal or dizygotic twins. Identical/monozygotic twins are a result when one egg is fertilized by one sperm, and then the egg separates to form two genetically identical halves (usually of the same-sex).

Another type known as conjoined/Siamese twins are a type of identical but during splitting, the embryo doesn't separate well, leading to attached babies. The fraternal or dizygotic twins are however formed in a slightly different manner, where there are two eggs fertilized by two different sperms, and these can have different sexes along with other differences. In this article you will read more about fraternal twin facts, so don't go anywhere as there's a lot more to learn!

Formation of Dizygotic Twins

• Fraternal or dizygotic twins are quite unusual cases which are not as dominant as monozygotic twins. Usually, during ovulation in a woman's menstrual cycle there is a single egg which is released into the uterus.
• If there is intercourse at this time, the sperms that enter, fertilize this egg which is then planted in the mother's womb to give rise to an offspring. But the formation of twins is slightly different, as there are variations in the process of fertilization.
• Sometimes, during ovulation, it so happens, that both the eggs are released in the uterus at the same time and with the right chances, there are two sperms which reach them. Fertilization takes place between both the sperms and during fertilization there is an exchange of chromosomes. This is known as Superfecundation.
• Another reason could be due to Superfetation, where the mother is already pregnant and ovulates a second egg, which is also fertilized by a separate sperm. Though the conception times of the two babies are different, the delivery can be at the same time as the mother is solely responsible for fraternal twins.
• During fertilization of dizygotic twins, there is exchange in genetic material and this is what gives rise to the two offspring traits.
• The two zygotes are developed in two different placentas and thus are not attached to each other in any way. They only share the mother's womb for development and nutrition, and are born at the same time. There can be complications in the birth times of these offspring, as they belong to two different placentas and may not come out at the same time!

Characteristic Traits of Fraternal Twins

• Now that you know what are fraternal twins, let's find some numbers and characteristics. According to statistics, there are about 75% of twin population who are fraternal twins, as the number has increased in recent times. Since the two offspring are completely different right from the time of conception, they also acquire different characteristics, both from the mother and the father.
• The "XX" of the mother combines with the "XY" chromosomes of the father and lead to various combinations that define the traits of the two offspring. Because there are two sets of these "XX" and "XY" for the two offspring, the genders, physical appearances and personalities are very different.
• During the fertilization of the first egg, the "X" from the father combines with the "X" from the mother, it leads to "XX" which gives rise to a baby girl. Similarly, when the "Y" from the father combines with the other "X" of the mother, a baby boy is produced.
• There are many other combinations which not only define the gender of the offspring, but also the physical appearances like height, color, hair, looks, etc., and personalities. Fraternal twins are as varied as any other siblings born years apart from each other, but are twins only because they share a womb at the same time.

With this interesting information about dizygotic twins, I am sure you have learned a lot about them. Twins remain nature's secret till today and they will always be a fascination for the people around them.