Are Boy And Girl Twins Identical

Can a Boy and Girl be Identical Twins?

When we hear the term “identical twins” we usually imagine two children that look exactly alike, have the same DNA, and share the same features. However, there is a common misconception about whether a boy and girl can be identical twins. In this article, we will explore the answer to this question in detail.

What are Identical Twins?

Identical or monozygotic twins develop from a single fertilized egg that splits into two embryos. These twins have the same genetic material and therefore, look very similar, if not exactly alike. They share the same blood type, eye color, skin tone, and other physical traits.

The splitting of the egg can occur in the first three days after fertilization, which produces two separate embryos with their own amniotic sacs. In some cases, the embryo splits between the fourth to ninth day of conception, resulting in conjoined twins.

What are Fraternal Twins?

Unlike identical twins, fraternal or dizygotic twins develop from two different eggs that are fertilized by two different sperm cells. As a result, they share only 50% of their genetic material, and therefore may not look alike. They can be the same gender or different genders.

Fraternal twinning runs in families and happens when a woman’s ovaries release two eggs simultaneously instead of one, which might be fertilized by different sperm cells.

Can a Boy and Girl be Identical Twins?

The answer is no, a boy and girl cannot be identical twins. The reason is quite simple. Identical twins occur when a single fertilized offspring splits into two embryos. Since the gender of the child is determined at the time of fertilization by the presence of X or Y chromosomes in the sperm, both embryos will have the same sex. Therefore, it is impossible for a boy and girl to be identical twins.

However, there is a rare exception to this rule. Sometimes, a genetic mutation in one of the twins occurs shortly after conception and causes one twin to develop male or female traits unexpectedly. This is known as ‘chimerism’ and it happens when one embryo absorbs the other, leading to two types of cells in one body. In some instances, it has been observed that male and female characteristics are present in one individual, technically making them their own fraternal twin.

What are Polar Body Twins?

In some cases, what appears to be a boy and girl identical twin is actually a chimera. Another possible explanation is the phenomenon of polar body twinning. This occurs when a developing embryo engulfs the polar body of its sibling, which is a small nonfunctional cell that normally contains half the genetic material of an egg. The embryo may then inherit chromosomes from both polar bodies, producing a mix of XX and XY chromosomes that express themselves as male and female traits, respectively.

While polar body twinning is interesting, it remains a topic of debate among scientists. There is not enough scientific evidence to prove that this phenomenon leads to the formation of boy and girl identical twins.


In conclusion, boy and girl identical twins do not exist naturally. The conception process makes it impossible for two embryos to be of different genders while having the same DNA. Although there are rare exceptions to the rule, they are more of a genetic anomaly than actual boy and girl identical twins. Identical twinning is a fascinating mechanism in nature that impacts the lives of millions of people worldwide and continues to pique the interest of geneticists, scientists, and researchers alike.

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