Mirror Identical Twins: What Are They & Their Charactertics

Mirror Twins – Causes & Characteristics

Medically Reviewed By
Dr. Rima Sonpal (Gynecologist/Obstetrician)
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Nowadays, giving birth to twins is fairly common. When you are expecting twins, many parents hope to have a boy and a girl. But, do you know that you can give birth to mirror twins as well? For those wondering what mirror twins are, this article is a must-read.

You must be aware of fraternal twins and identical twins. Fraternal twins are formed when 2 eggs released at the same time are fertilised by two different sperms simultaneously, resulting in 2 genetically different children. Identical twins (monozygotic twins) are formed when one fertilised egg splits into two and develops into 2 babies with the exact same genetic information. Identical twins look very much alike and have the same genetic material.

Mirror Twins or mirror image twins are a type of identical twins. Their features appear on opposite sides, like a mirror image. For example, one mirror twin may have a mole on her left cheek, and the other twin will have the same mole on her right cheek.

What Are Mirror Twins?

Mirror twins or mirror identical twins are twins whose features appear asymmetrically or on the opposite sides. Identical twins have the same sex and share the same blood type. Mirror twins have identical but asymmetric physical features. For example, one twin could be left-handed, and the other could be right-handed. In extreme cases, mirror twins may have mirrored internal organs, where the placement of internal organs may be reversed in one of the twins.

Causes of Mirror Twinning

Mirror image twinning occurs because of the late splitting of the fertilised egg. For regular identical twins, the egg splits into two between 2 and 8 days of conception. In the case of mirror twins, the egg splits into 2 much later, between 9 and 12 days of conception. This causes the twins to mirror each other.

Is There Any Test to Detect a Mirror Pair?

While identical twins can be detected with a DNA test as they share the same genetic material, it is not possible to determine if they are mirror twins by genetic testing. An examination of the physical characteristics has to be done to find out if the identical twins are actually mirror twins.

Is There Any Test to Detect a Mirror Pair?

Characteristics of Mirror Image Twins

Mirror image twins may have several characteristics that are reversed. Some of these are:

  • Birthmarks and moles – They may appear asymmetrically in mirror twins. For example, one twin will have a birthmark or mole on the right side of the cheek, and the other will the same mole on the left cheek. One may have a birthmark on the right leg, while the other will have the exact same birthmark on the left leg.
  • Freckles and dimples – These are also asymmetrical in mirror twins. For example, if one has a dimple on the left side of the chin, the other will have the dimple on the right side of the chin. The pattern of freckles can also be asymmetric in mirror twins.
  • Hand orientation – Hand orientation is usually asymmetric in mirror twins. For example, if one twin is right-handed, the other is usually left-handed.
  • Hair whorls – Mirror twins may have hair whorls in opposite directions. If one twin has hair that swirl clockwise, the other may have hair that swirl counterclockwise.
  • Eye shape and eyebrow shape – Eye shape and eyebrow shape can also be reversed in mirror image twins. For example, if the right eye is slightly smaller in one twin, the left eye of the other twin will be small.
  • Ear shape – Ear shape can also be asymmetric in mirror twins. The ridges and bumps of the outer ear are unique to every individual. This can be reversed in mirror twins.
  • Nostril shape – The shape of the nostrils may also be asymmetric in mirror twins.
  • Organs – In extreme cases, which is rare, the positioning of the internal organs may be opposite in mirror twins. This is called ‘situs inversus’, where internal organs like the heart, stomach or liver are found on the opposite side of their usual anatomical position.
  • Mirror Twins’ Personality – Mirror image twins may also have opposite personalities. For example, one may be highly introverted, while the other may be an extrovert. One may prefer sleeping on the right side, while the other may prefer sleeping on the left side.

Difference Between Mirror Twins and Identical Twins

Identical twins are monozygotic, which means a single fertilised egg splits into two and forms two embryos that share the same genetic material. Identical twins are formed when the egg splits into two between day 2 and day 8, while mirror twins are formed when the egg splits late, between day 9 and day 12 causing the twins to mirror each other. If the egg splits after 12 days, it results in conjoined twins, where the twins are not completely separated from each other and may even share an organ.

Mirror twins are identical twins, and their characteristics mirror each other. All mirror twins are identical twins, but all identical twins may not be mirror image twins.

Mirror twins are a fascinating type of identical twins. Not every set of mirror-image twins will be opposite-handed or will have moles on the opposite sides. This is because the degree of mirror imaging differs for every set of twins.

Also Read: Vanishing Twin Syndrome

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