Identical twins have different fingerprints. Twins can have completely different skin tone. Twins start interacting in the womb at 14 weeks. Identical twins can develop different diseases.
Identical twins have DNA that is 99.9% the same. They also have almost nearly identical brain wave patterns. But they do have different fingerprints and teeth marks! 22% of twins are left-handed as opposed to the 10% of singletons who turn out to be left-handed.
Because identical twins develop from a single fertilized egg, they have the same genome. So any differences between twins are due to their environments, not genetics. Recent studies have shown that many environmentally induced differences are reflected in the epigenome.
Identical twins share all of their genes, while non-identical twins, just like non-twin siblings, share half of their genes. So, we can assume that any differences in traits between identical twins come from the environment, and not from differences in their genes.
Thus identical twins, though they start with the same genes, likely develop different personalities in the same environment partially based on how they interact with their environment.
Monoamniotic-monochorionic Twins
This is the rarest type of twin, and it means a riskier pregnancy as the babies can get tangled in their own umbilical cords. If you have monoamniotic-monochorionic twins, your healthcare provider will monitor your pregnancy closely.
"Twins tend to be closer than typical siblings — they share a bond that is oftentimes unexplainable," Maureen Healy, an expert on sensitive children and author of Growing Happy Kids, tells Romper. "Many believe this is rooted in genetics, such as identical twins sharing the same DNA."
Classically, the bigger twin is the more physically dominant. It's basic human nature, and particularly applicable to boys as they hit puberty. It happens often with singleton siblings too… the older is bigger and enforces him/herself through physical dominance.
Key points. Competition, jealousy, sharing, and expectations make twinship a hard relationship to navigate. Twins are sometimes confused as to who they are in relationship to each other. It's important not to make twins feel guilty or ashamed if they don't get along.
Identical twins are almost always the same sex, although there are some rare exceptions to this rule. Because identical twins occur when a single fertilized egg splits and forms two embryos, each embryo has the same chromosomes (usually, XX for girls or XY for boys).
Identical twins reported similar levels of happiness, while fraternal twins exhibited greater variation in their reported sense of well-being. These results were found in families of twins raised together and extended with twins reared apart.
In ancient times, the Yoruba viewed twins with suspicion, and sometimes sacrificed them. But now twins are considered lucky. In contrast to the Western view, the firstborn twin is considered the younger of the two. The Yoruba believe that the "senior" twin sent the younger one out first to scout the world.
Fraternal twins live longer than singletons and identical twins longer still. Male identical twins on average, saw the most benefit. The rarity of twins has inspired many myths about them.
Longer lives
When analyzing the data by gender, the researchers found that female identical twins lived, on average, about 63.4 years, whereas female fraternal twins lived about 61.4 years and the general Danish female population lived about 58.8 years, Sharrow said.
What are the benefits for the twins? Their buddy is always there. They've known each other since they can remember and that is very comforting. They are also a little more social than the average child since they are used to being with another kid since the beginning.
That difference is about 6 percentage points, meaning that if out of 100 boys in the general population, 84 were still alive at age 45, then for twins that number was 90. For women, the peak mortality advantage came in their early 60s, and the difference was about 10 percentage points.
Identical (i.e., monozygotic, or MZ) twins share 100 percent of their genes, whereas fraternal (i.e., dizygotic, or DZ) twins generally share only 50 percent of their genes.
Some say that twins are always hard (yet amazing), while others say they truly didn't find them to be difficult. A few said that the first two months with twins are easy (being in the rose-colored glasses phase), then reality hits from months 3-6 (when the sleep deprivation catches up), then it can get easier again.