Although identical twins have the same genes, they don't always look the same. This is because children's health and development are shaped not only by genes but also by experiences in the womb and after birth. For example, a twin who gets less blood from a shared placenta might weigh less at birth.
Things like your eye and hair color are controlled by your DNA. This is why identical twins look so much alike -- they share the same DNA. And yet, they aren't exactly alike. They can be hard to tell apart but if you look closely, you see differences.
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.
Fraternal or 'dizygotic' twins
Around two in three sets of twins are fraternal. Two separate eggs (ova) are fertilised by two separate sperm, resulting in fraternal or 'dizygotic' (two-cell) twins. These babies will be no more alike than siblings born at separate times.
As a result of the environment, chemicals called “epigenetic marks” attach to the chromosomes and can turn specific genes on or off. So identical twins with identical DNA may have different genes turned on, causing them to look and act differently, and even to develop different diseases such as cancer.
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.
Yes, it is possible for same-sex fraternal twins to look extremely similar.
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.
Everyone has the same chance of having identical twins: about 1 in 250. Identical twins do not run in families. But there are some factors that make having non-identical twins more likely: non-identical twins are more common in some ethnic groups, with the highest rate among Nigerians and the lowest among Japanese.
They come from the same fertilized egg and share the same genetic blueprint. To a standard DNA test, they are indistinguishable. But any forensics expert will tell you that there is at least one surefire way to tell them apart: identical twins do not have matching fingerprints.
Identical twins share the same genomes and are always of the same sex. In contrast, fraternal (dizygotic) twins result from the fertilization of two separate eggs with two different sperm during the same pregnancy. They share half of their genomes, just like any other siblings.
Like for their twin parents, there are many fascinating family relationships for the children of twins–when identical twins have children, their children are cousins but genetically as similar as half-siblings.
Just like your fingerprint, your teeth are completely unique to you. In fact, dental records can be used to identify human remains because even identical twins don't have the same teeth. Your tongue also has its own print that's completely different from any other.
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. (Ashley is two minutes older too, FYI.)
In the mother's womb (uterus), most identical twins share the same placenta. (They get oxygen and nutrients from the mother and get rid of wastes through the placenta.) But they usually grow within separate amniotic sacs. In rare cases, identical twins share one amniotic sac.
#1 Fraternal twins can be conceived as much as 24 days apart
For this reason, fraternal twins can be conceived a few weeks apart, though they generally will be born at the same time.
Twins are at increased risk of fetal and infant death compared with singleton births. 1-3 The increased risk is partly the result of the lower birthweight and gestational age at delivery of multiple pregnancies. At particular risk are monozygotic twins who have poorer survival rates than dizygotic twins.
The first wife (died ante 1770), of Feodor Vassilyev (b. 1707–c. 1782), a peasant from Shuya, Russia, gave birth to 16 sets of twins.
The worlds heaviest twins, with an aggregate weight of 12.58 kg (27 lb 12 oz), were born to Mary Ann Haskin (USA), of Fort Smith, Arkansas, USA on 20 February 1924.
Homopaternal superfecundation is fertilization of two separate ova from the same father, leading to fraternal twins, while heteropaternal superfecundation is a form of atypical twinning where, genetically, the twins are half siblings – sharing the same mother, but with different fathers.
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.
A dad who's one of a twin may inherit the gene, but it won't increase his chances of having twins too, because the gene only affects ovulation. The same dad may pass on the gene to his daughter, who then goes on to get pregnant with twins, making it look like twins have skipped a generation .
The study appears in Behavior Genetics. ASD is a developmental disorder that affects how a person behaves, interacts with others and learns. Previous studies have found that when one identical twin has ASD, chances are extremely likely that the other twin has it, too.