Since identical twins share the same DNA, the children of two pairs of identical twins are legally
"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."
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.
Fraternal twins are no more genetically similar than any other pair of siblings who share biological parents. That's because each egg and each sperm contain different genes, Dr. Peskin explains. The genes in each egg and each sperm are some combination of the genes inherited from parents.
Identical, or monozygotic (MZ), twins have 100 percent of their genes—including those that influence risk for alcoholism—in common, whereas fraternal, or dizygotic (DZ), twins share (on average) only 50 percent of the genes that vary in the population (see figure). Common Environmental Sources.
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.
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.
And because the death rate in the womb is higher for twins than for singleton births, female twins are more common than male twins.
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).
According to the Office on Women's Health , women who are aged 30 years or older are more likely to conceive twins. The reason for this is that women of this age are more likely than younger women to release more than one egg during their reproductive cycle.
Dizygotic (DZ) twins, also called fraternal twins, occur when two egg cells are each fertilized by a different sperm cell in the same menstrual cycle. DZ twins are about twice as common as MZ twins, and they are much more likely to run in families.
Since identical twins share the same DNA, the children of two pairs of identical twins are legally cousins, but genetically more similar to siblings.
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 come from a single fertilized egg that splits in half, while fraternal twins occur when two different eggs are fertilized simultaneously). So, how many months apart are Irish twins? It's technically possible for two siblings to be as close as 9 or 10 months apart.
A twinless twin, or lone twin, is a person whose twin has died. Twinless twins around the world unite through organizations and online groups to share support and the status as a twinless twin.
They are the result of one fertilized egg splitting into two, giving them identical DNA. (Fraternal twins are the result of two separate, genetically different fertilized eggs.) As a result, identical twins are as close as two people can be. They can speak in unison (it's weird at first, then charming).
The quick answer to this question is that, in a twin pregnancy, it is the mother's genes that determine twins. First up, giving birth to identical twins is not genetic, but conceiving fraternal twins is. The mother may have the genetic trait of releasing two eggs in one menstrual cycle.
There is no evidence of twin telepathy. There are many myths about twins—hence, the title of my new book, Twin Mythconceptions: False Beliefs, Fables, And Facts About Twins (2017, Elsevier).
Factors that increase the chance of twins include: consuming high amounts of dairy foods, being over the age of 30, and conceiving while breastfeeding. Many fertility drugs including Clomid, Gonal-F, and Follistim also increase the odds of a twin pregnancy.
If twins are a boy and a girl, clearly they are fraternal twins, as they do not have the same DNA. A boy has XY chromosomes and a girl has XX chromosomes. Girl-boy twins occur when one X egg is fertilized with an X sperm, and a Y sperm fertilizes the other X egg.
Mixed-gender twins are the most common type of fraternals, some 50 percent are boy-girl. To understand this combination: Males have XY chromosomes, females have XX chromosomes.
Still, she cautions, a lot more work needs to be done to establish a causal link. Fraternal twins, in which each of two eggs is fertilized by a different sperm cell, occur in about four of every 1000 births. About half of those result in male-female twin pairs.
Monozygotic (identical) twins will have the same blood type, with a few very rare exceptions. Dizygotic (fraternal) twins may have the same blood type, or they may have different types. Therefore, it may be concluded that twins with differing blood types are dizygotic, or fraternal.
Identical twins have exactly the same DNA, but they are not exactly alike. Each twin has his or her own personality, talents, likes, and dislikes. There are even diseases that appear in one twin but not the other, including arthritis, diabetes, autism, schizophrenia, cancer, and many others.
"[Two sets of] identical twins will not have identical offspring," says Professor Rodney Scott, head of medical genetics at the University of Newcastle. The only way we get identical offspring is when a fertilised egg splits into two cells. "Those identical cells grow into identical twins," says Scott.