10 Facts About Fraternal Twins That You Probably Didn’t Know

Despite popular perceptions of most twins being identical, fraternal/non-identical twins are more prevalent in real life. Fraternal twins each come from their own egg and sperm. Identical twins are monozygotic while Fraternal twins are dizygotic. Zygotic refers to zygote, the egg fertilized by the sperm that will develop into an embryo. Monozygotic twins come from a single egg and sperm that splits into two after conception.

10 Fraternal Twins Facts

1. They are formed from two different eggs

Fraternal twins are dizygotic, i.e. formed from fertilization of two separate eggs. Each fertilized egg develops into an embryo and then a baby. Monozygotic twins or identical twins originate from a single fertilized egg which splits into two, after conception.

2. The twins can be caused by other factors

Many factors influencing multiple births are able to only impact fraternal twinning. Heredity, birth control pills, and diet can all decrease the chances of the woman of producing multiples, but only dizygotic multiples. That is because all of these factors may encourage hyperovulation, that causes the release of more than one egg per cycle and increase the chances of having twins.

3. They can either be of both gender or the combination of boys and girls

As fraternal twins originate from separate conceptions, they can either be all boys, girls, or one of each. The gender is determined by father’sperm. Usually, the chances of fraternal twins being boys, girls or a combination of both are the same as for any normal babies. Identical twins (Monozygotic), on the other hand, are always of the same gender. Fraternal twins can be two boys, two girls or one girl and one boy.

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4. The twins are as genetically similar as any other siblings.

Like brothers and sisters, fraternal twins will have about half of their genetic makeup in common. They share about 50% of their DNA, the same as any siblings. Both individual receives half of their DNA from Mother’s egg and the half from the father’s sperm, and so the two offspring will have some overlapping qualities.

5. The twinning rate varies across populations

Not every population has the same rates of twinning. Studies have shown that some groups of people have twins much more frequently, while twins are rare among other groups. In 2011 one study had shown that the highest rates of twinning were found in Central African populations.

6. The twins may or may not look or act alike

Monozygotic are identical as they often have similar appearances and characteristics. Fraternal twins are as almost like two siblings. They may look similar or even identical or they might look very different. They can have different eye color, hair color, different stature, different personalities. They may be so similar that they are assumed to be identical, just as some siblings would be remarkably indistinguishable, if only they were the same age. The environment also plays an important in making them similar. If they are raised in the same home, share the same experiences, and are educated in the same classroom then there is a possibility that they will be similar.

7. They have two placenta

Placenta provides vital substance to the baby. When multiple pregnancies with fraternal twins occur, two placenta develops for each baby. However, they fuse together and appears to be a single placenta. Some monozygotic twins have one placenta, which can make it difficult to determine the zygosity in the uterus. Since they have their own placentas, fraternal twins are not at risk for some of the risky conditions which affect the monozygotic twins, such as monoamniotic twins and TTTS.

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8. Fraternal twins can be influenced by heredity

Fraternal twins occur when more than one egg is fertilized. Usually, one egg is released during ovulation, but sometimes more than one egg is released. Women who hyperovulate are more likely to have fraternal twins. In this way, fraternal twinning can be hereditary. The woman can pass it down to her daughter. Then the daughter’s chances of having twins will increase. As men carry both X (female) and Y (male) chromosomes, they might also have the trait for hyperovulation and pass it along with their daughters, which increases their daughter’s chances of having fraternal twins. However, this d does not increase a man’s chances of fathering fraternal twins. Men might carry the gene, but they do not ovulate. That is why twins are sometimes known to skip a generation.

9. Fraternal twins may be conceived at different times or by different fathers

Normally one egg is released during ovulation. But when hyperovulation occurs, multiple eggs are released. This can happen in an interval of few days. When an egg is fertilized it begins to travel to the uterus for implantation. The other egg can be fertilized by sperm from a later act of sexual intercourse. This can result is fraternal twins who are actually conceived a few days apart. This phenomenon is known as superfetation. There have even been cases of fraternal twins having different fathers. This may occur if a woman is hyperovulating and has sexual relations with more than one partner. One egg is fertilized by sperm from one man and the other one egg from another man, then fraternal twins with different fathers are born. This phenomenon is known as superfecundation.

10. Fraternal twins might be due to the result of fertility treatments

newborn Baby’s hand

As the advancement of became medical treatment became more accessible, the twin birth rate increased rapidly  Fertility treatments like IVF and some drugs like Clomid sometimes results in the production of twins or multiples, with the majority of multiple births being dizygotic. Some instances of monozygotic twinning do occur in IVF.

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