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Identical Twins

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Identical Twins: Different Types of Twins

Identical twins can be defined as twins who have similar features due to the division of the fertilized egg. Multiple births are more common these days than they actually were in the past. One of the main reasons for this could be the advancement in the ages of mothers who are pregnant. 

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Not to mention that there is also a rise in the different reproductive techniques that assist in facilitating the pregnancy such as fertility drugs and other methods. As a result, twins hold a major share of the multiple birth section. Some of these births are identical twins and some of them are non-identical or fraternal. In this article, students are going to learn how are identical twins formed along with other details such as the types of twins that are born.

Difference Between Identical and Non Identical Twins 

In order to form identical twins, a particular egg or ovum that has been fertilized will split into two different halves. Each one of the halves will actually grow in order to form a baby. Hence, the genetic information in both the eggs will be the same. Identical twins can be a lot different from fraternal or non-identical twins. In the case of non-identical twins, two different eggs are fertilized by 2 different sperm cells and hence produce 2 different and genetically unique children. These children are not much unlike the individual children who are born in different times. 

What are Identical Twins? 

According to the National Library of Medicine, identical or monozygotic twins are basically conceived from a single egg that is fertilized. The fertilized egg will separate to form 2 different embryos after the division process begins. In an identical twins pregnancy, the embryos will develop into 2 different and yet identical looking babies. While in some cases, the physical features might not be alike, these babies tend to share the same genetic material which is the chromosomes. This is due to the fact that both the babies are conceived from the same sperm cell and ovum. They are also assigned the same sex with their birth as well as the same genetic characteristics. 

Non-Identical Twins 

All the twins that are born aren’t identical. Twins tend to have unique characteristics. Non identical twins are also called fraternal twins and Dizygotic twins. The term comes from two fertilized eggs or ovum that are fertilized by 2 different sperm cells. Hence the non-identical twins are separate babies that are born at the same time. This situation occurs when the mother releases 2 different eggs at the same time period. Different sperms tend to fertilize the eggs. Given that the fraternal twins tend to have different eggs, they share the chromosomes like individual siblings. This is one of the main reasons why these twins aren’t assigned the same sex during their birth and don’t have identical physical characteristics. 

The Third Type of Twins 

In a traditional sense, twins are just of two types. However, some scientists argue that there are 3 types of twins. This theory hasn’t been confirmed yet. According to research, there is a reason why some fraternal twins tend to share some physical characteristics. After getting released from the ovary, the egg splits into two different halves. One of the eggs which is smaller will be known as a polar body. Hence, the polar body possesses all the important chromosomes that are essential for creating the baby. 

However, since the body doesn’t have the required amount of fluid, it is difficult for it to survive. But it is possible that the polar body survives and is fertilized. Meanwhile, the separate part of the egg that is larger will get fertilized by another sperm. Hence, the creation of polar twins occurs. The polar twins tend to have the same chromosomes that come from the birthing parent. However, they also get different chromosomes from the parent who is not birthing them. Hence, the creation happens from different sperm cells but the same egg. 

Gestation Process for Twins 

The gestation period is the period in which the baby is formed. The normal duration for gestation is about 40 weeks in total. However, in the case of twins, whether they are fraternal or identical, is about 38 weeks in total. The time period for the gestation of twins tends to be shorter due to the increase in demand for the body of the mother. The twins’ inability to properly receive all important nutrients could also be another one of the reasons for the shorter period of gestations. One of the most important things to keep in mind about identical twins’ birth is that they are mostly premature. Hence, they tend to have birth weights that are relatively lower than normal children. 


The above-mentioned article provides an explanation about identical twins and how they are formed. Students can use this article to learn more about identical twins facts and other details.

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FAQs on Identical Twins

1. What are identical twins?

Twin births are pretty common events that happen these days. There are two different types of twins and they are identical and non-identical or fraternal twins. In the case of identical twins, the egg, when fertilized, is split into two different halves. In this case, the egg is fertilized by a single sperm cell and after splitting, both the embryos will share the same chromosomes of the birthing as well as the non-birthing parent. These twins are assigned the same sex during birth and also share the same genetic characteristics as well. However, there is a chance that these twins might not have the same physical characteristics.

2. What is the difference between identical and non identical twins?

In the case of identical twins, the fertilized egg uses just one sperm for the process of fertilization. After that process is complete, the egg will then split into two different parts and create two different embryos. As a result, the babies that are born identical will share the same genetic characteristics and also share similar physical characteristics too. However, in the case of non-identical twins, the female body releases two different eggs which are then fertilized by two different sperm cells. Hence, the creation of fraternal twins means that the babies will not share the same chromosomes and hence will not have the same genetic or physical characteristics.

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