In 99.9% of cases boy/girl twins are non-identical. However, in some extremely rare cases resulting from a genetic mutation, identical twins from an egg and sperm which began as male (XY) can develop into a male / female pair.
Twin Zygosity
The "di" in dizygotic means two, as in deriving from two zygotes (fertilized eggs). The terms identical and fraternal don't describe what the twins look like, but actually how they form. 1 Dizygotic twins may be the same sex or different sexes, just like siblings born in separate pregnancies.
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.
The majority of triplets are what is known as trizygotic. This is because they are formed when three separate, individual eggs are fertilised by three separate sperm. These babies share the same characteristics as any other siblings with the same biological parents. They can be the same or opposite genders.
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.
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.
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.
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.
The Dionne quintuplets (born 28 May 1934, near Corbeil, Ontario, Canada) were the first quintuplets known to survive infancy. The five girls (Yvonne, Annette, Cecile, Emilie and Marie) were also the only set of identical quintuplets known to live into adulthood.
Since conception happened for each egg, each egg carries the sex chromosome of the father. A girl has XX chromosomes while a boy has XY chromosomes. A boy-girl combination is the most common form of these kind of twins.
Baby gender is decided by men's sperm. Sperm cell with X chromosome will produce girls and when egg is fertilized by sperm cell with Y chromosome, a baby boy is born. The only SURE WAY for desired-sex baby is IVF treatment with PGD (preimplantation genetic diagnosis).
At first blush it might seem impossible they could look so different. After all, while huge differences can and do happen with fraternal twins, identical twins are usually exactly that -- identical in skin, hair and eye color.
Mirror twins, or mirror image twins, is a term used to describe a characteristic of some twins whose features appear asymmetrically—that is, on opposite sides. When these twins are facing each other, it is as if they are looking in a mirror.
They found just one other instance of semi-identical twins, which was reported in the United States in 2007. In that case, doctors didn't realize that the twins were sesquizygotic until after they were born, when one of them was found to be intersex, meaning that they had ambiguous genitalia.
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.
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).
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.
Superfetation is a rare event that involves getting pregnant a second time while you're already pregnant. It's so uncommon that cases of superfetation often make headlines. Your body does a good job preventing subsequent pregnancies once an embryo is developing inside your uterus.
A rainbow baby is a child born after the loss of a previous pregnancy or newborn.
From watching "The League," we're heard the term Eskimo Brothers for dudes who've slept with the same girl. Urban Dictionary, the source for all things slang, likewise defines Eskimo Sisters -- or Pogo Sisters -- as "two women [who] have slept with the same man in their past."
Race. African-American people assigned female at birth are more likely to have twins than any other race. Asian Americans and Native Americans have the lowest rates for twins. White people assigned female at birth have the highest rate of higher-order multiple births (triplets or more).
#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.
“Having twins is not twice as hard—it's exponentially more difficult,” says Natalie Diaz, author of What To Do When You're Having Two and CEO of Twiniversity, a global support network for parents of twins.