For Quadmama: How Identical Is Identical?

Quadmama asked: How identical are identical twins? Do they share the same blood type and fingerprints?

I love this question.

“Identical” or monozygotic twins are twins created from a single fertilized egg (as opposed to a multiple eggs fertilized with multiple sperm or fraternal twins).

How alike are they? Very alike. In theory, they a genetically identical. Except for very unusual cases, they are the same gender and have the exact same set chromosomes. But how alike are they practically?

You asked about blood type . Theirs should be identical since that is genetically driven (though, again, there are unusual diseases and operations that can change it, but it's very unlikely that any of those things could happen.

Fingerprints, however, are influenced by environment and apparently created by our skin glands. The are also affected by wear and scars. For those reasons, identical twin would have individual (i.e. different) fingerprints.

Other genetic traits may not be identical. As children grow, different genetic factors can turn off and on, even though the genes are present identically. For that reason, a twins who have a genetic predilection for diabetes does not guarantee that both will get it, or if one does, the other one will. They have the same genes, but they aren't necessarily using those genes the same way. The older the twins, the more pronounced those changes (and, if the environments are different, that also increases those changes).

Personalities, naturally, are not interchangeable and radically different environments (like adopted twin separated young) will show more differences than twins growing up together. However, similarities, even among twins that have never know each other, argue genetics play a part as well.

It's a fun topic, and I'm glad you asked, quadmama.