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While identical twins have almost every physical attribute in common, they won’t have the same birthmarks. Why? It’s all about their development in the womb. My identical twin girls, for example, don’t have the same birthmarks.
Identical twins, also known as monozygotic twins, originate from the same fertilized egg, yet they can have different birthmarks due to several factors:
1. Environmental Factors
During the twin pregnancy, variations in the uterine environment can affect the development of each twin differently.
Factors such as differences in blood flow, nutrition, and space in the womb can lead to distinct physical features like birthmarks.
As you’ll see during ultrasounds, your twins are in a constant state of wrestling with each other for space in the womb.
The unique position each twin occupies in the womb can also influence these differences.
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Depending on their position, one twin may receive a slightly different distribution of blood flow and nutrients from the placenta. This can influence the development of their skin and the likelihood of forming birthmarks, as adequate blood supply and nutrients are crucial for uniform skin development.
The position of each twin in the womb can result in varying levels of pressure and friction against the uterine wall or against each other. Increased pressure or friction in certain areas may affect skin development, potentially leading to birthmarks such as hemangiomas, which are often related to vascular abnormalities.
As the pregnancy progresses, space in the womb becomes limited, especially with twins. If one twin is more compressed or experiences more pressure in a particular area, this could lead to differences in skin development, including the formation of birthmarks
2. Random Mutations
As cells divide and develop, spontaneous mutations can occur.
No, this doesn’t mean your twins will be X-Men like Wolverine.
Even though identical twins share the same DNA, minor genetic mutations can happen during the DNA replication process.
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These mutations may cause differences in skin pigmentation and birthmarks.
Don’t worry, mutations during pregnancy are a natural part of human development and can occur at various stages.
On average, every human carries about 50-100 new mutations that were not present in their parents. These mutations can occur at any point from the formation of the zygote to the development of the fetus.
A study in Nature Genetics found that mutations can occur very early in the development of twins. Among 381 pairs of monozygotic twins, an average of 5.2 genetic mutations were found between each pair, with some pairs differing by more than 100 mutations.
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3. Epigenetic Changes
Epigenetics involves changes in gene expression that do not alter the DNA sequence but affect how genes are turned on or off. These changes can result from environmental influences and lead to differences in physical characteristics between twins, including birthmarks. As twins age and experience different environments, their epigenetic markers can diverge, further contributing to differences.
Epigenetic changes are common during pregnancy and play a crucial role in fetal development. These changes can be influenced by various factors and have lasting effects on the health and development of the child.
Research has shown that identical twins, despite having the same genetic material, can exhibit differences in traits due to epigenetic variations.
Overall, epigenetic changes during pregnancy are a common and essential part of human development. They are influenced by both genetic and environmental factors and can have significant implications for the health and development of the babies beyond just birthmarks.
4. Chimerism and Mosaicism
In rare cases, chimerism can occur, where one twin absorbs some cells from the other during development, leading to unique physical features.
Mosaicism can also contribute to differences in appearance, where a mutation affects some cells but not others, leading to variations like birthmarks.
As you can see, there are many factors that could lead to your twins having different birthmarks.
Birthmarks aren’t the only thing that will be different with your twins. They will have different fingerprints too.
