Identical twins have identical genes, because they are born of an embryo that splits at a very early stage in development. Such twins are often indistinguishable in outward appearance. But over the course of time they may experience radically dissimilar health.
Identical twins are genetic carbon copies, meaning their DNA sequencing is the same. Yet physically they become increasingly different over time.
DNA Differences
Each clump of cells goes on to become one of the identical twins. In this process of becoming a brand new baby with trillions of cells, the cells in each clump divide over and over again. DNA differences or mutations can happen any time a cell divides.
Research published on January 7 in the journal Nature Genetics shows that identical twins differ by an average of 5.2 genetic mutations.
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.
While there are risks associated with all twin pregnancies, dizygotic (fraternal) twin pregnancies usually bring about the least amount of complications, carrying the lowest risk of all types of twins. Worse complications are possible with monozygotic (identical) twins because the embryo is dividing.
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.
Twins not only have a bestie from birth — they also live longer than singletons. And those two factors may be related, according to new University of Washington research.
Scientists have shown that identical twins have very similar marks when they are born. But, as they age, the marks in their DNA become more and more different. So even though identical twins have the same DNA, they are using it in different ways.
Environmental Differences
While identical twins form with the same set of genes, human development is not just genetic. The environment also has an impact. 1 So, beginning in the early environment of the womb, external influences can change the appearance of twins.
Identical twins are completely random. It's not based on family history or genetics. Identical twins form when a single fertilized egg splits and forms two embryos. Now in this case, it's not because of mom or dad.
While many people can't tell them apart, Mary-Kate and Ashley are not identical, but rather fraternal: Mary-Kate is one inch taller than her sister and is left-handed, while Ashley is right-handed.
Despite having the same genetic makeup, identical twins have their own distinctive personalities. Just how their individuality emerges has remained a bit of a mystery. But now, researchers have found that life experiences affect brain development — and this may help us understand how personalities form.
The DNA of monozygotic twins tends not to be 100% identical, and epigenetic and environmental differences further widen the gap between twin pairs. It's not nature or nurture; it's a complex interaction between our genes, our environment, and our epigenetic markers that shape who we are and what illnesses befall us.
At age 7, the mean IQ score of twins was 5.3 points lower than that of singletons in the same family, and at age 9, the score was 6.0 points lower. The lower intelligence of twins in childhood may partly be a consequence of the reduced fetal growth and shorter gestations of twins, say the authors.
Identical twins will always have the same blood type because they were created from the same fertilized egg (fraternal twins can have different blood types — again, providing the parents do — because they are created by two fertilized eggs).
For a given pregnancy, the odds of conceiving fraternal twins are only determined by the mother's genetics, not the father's. Fraternal twins happen when two eggs are simultaneously fertilised instead of just one.
Having two babies at a time is associated with a longer life, according to a new study. But that's not because doubling up on dirty diapers increases life span; instead, moms of twins are physically stronger in the first place.
They examined reported levels of happiness in 1,300 sets of identical and fraternal twins. Identical twins reported similar levels of happiness, while fraternal twins exhibited greater variation in their reported sense of well-being.
Most twins are born healthy. A twin pregnancy can mean a higher chance of health complications so you'll need extra check-ups. Twins that share a placenta or inner sac need to be checked more closely. It's good to know whether twins are fraternal or identical for health reasons later in life.
Monozygotic (MZ) twins, also called identical twins, occur when a single egg cell is fertilized by a single sperm cell. The resulting zygote splits into two very early in development, leading to the formation of two separate embryos. MZ twins occur in 3 to 4 per 1,000 births worldwide.
Twins share the same genes but their environments become more different as they age. This unique aspect of twins makes them an excellent model for understanding how genes and the environment contribute to certain traits, especially complex behaviors and diseases.
Polar body twinning is thought to occur when an egg splits - and each half is fertilised by a different sperm. This results in twins who appear very much alike but share approximately 75% of their DNA.
If existing twins are identical the chance of having another set is the same as most women, about 1 in 250. If the twins are non- identical the chances of having twins again are much higher.
A big reason for all those twins is an increase in medically assisted reproduction, including in vitro fertilization, ovarian stimulation and artificial insemination. Another reason is that women in many countries are having babies at older ages.