No, not all twins mirror each other, but about 25% of identical twins are estimated to be mirror twins.
While all identical twins share nearly identical DNA, mirror twins exhibit reversed features, making one twin appear as a reflection of the other. This phenomenon arises due to the timing of the egg's division during development. If the split occurs later (between days 9 and 12 after fertilization), the twins are more likely to develop these mirror-image characteristics.
Characteristics of Mirror Twins:
Mirror twins can exhibit a variety of mirrored traits, including:
- Hair Part: One twin's hair might part on the left, while the other's parts on the right.
- Birthmarks/Moles: Birthmarks or moles might appear on opposite sides of their bodies.
- Dominance: One twin might be right-handed, while the other is left-handed.
- Dental Patterns: Even their teeth might exhibit reversed patterns.
- Internal Organs: In rare cases, internal organs can be positioned on opposite sides (situs inversus).
Why Does This Happen?
The exact cause isn't fully understood, but it's believed to relate to the timing of the egg's division. A later division allows more time for developmental factors to influence asymmetry. It's important to note that while the term "mirror twins" is commonly used, they are not perfect reflections. Rather, they possess specific, noticeable mirrored traits.
