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.
Twin genetics depend on what kind of twins we are talking about. Having identical twins is not genetic. On the other hand, fraternal twins can run in families. Genetics can definitely play a role in having fraternal twins.
Unlike identical twins—who are genetically the same—fraternal twins are no more closely related in terms of DNA than regular siblings.
Nobody knows what causes identical (monozygotic) twins. Everyone has the same chance of having identical twins: about 1 in 250. Identical twins do not run in families.
However, since only women ovulate, the connection is only valid on the mother's side of the family. While men can carry the gene and pass it on to their daughters, a family history of twins doesn't make them any more likely to have twins themselves.
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.
Yes, some types of twins run in families. Non-identical (fraternal) twins tend to be hereditary. Some people inherit a gene that causes more than one egg to be released during ovulation, increasing the likelihood of multiples being conceived. This can make for lots of twins down the generations!
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.
The notion that twins always skip a generation is also a myth. The illusion may have arisen because men who inherit the gene from their mothers are unaffected by it ( they do not ovulate), but can still pass it on to their daughters, who, in turn, will have an increased likelihood of conceiving 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).
In effect, though identical twins don't have identical DNA, they are genetically similar.
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.
So we wondered: can fraternal twins actually be identical? Fraternal twins who end up being identical is a small, often-debated percentage — between 3% and 20% usually.
Semi-identical twins are rare, and doctors say they've identified the second case ever | CNN. You've probably heard of identical and fraternal twins, but a report released this week says there's a third kind -- sesquizygous twins or "semi-identical." Researchers say they share anywhere from 50 to 100% of their genomes.
Professor Monden explained that, “The twinning rate in Africa is so high because of the high number of dizygotic twins – twins born from two separate eggs – born there." He continued, “This is most likely to be due to genetic differences between the African population and other populations.”
About one third of all twins are born vaginally and the process is similar to that of giving birth to a single baby. If you're planning a vaginal delivery, it's usually recommended that you have an epidural for pain relief.
Identical twins do not have identical fingerprints, even though their identical genes give them very similar patterns. 1 The fetus begins developing fingerprint patterns in the early weeks of pregnancy. Small differences in the womb environment conspire to give each twin different, but similar, fingerprints.
About 23 in every 1000 births are fraternal, a much higher rate than the three or four out of 1000 births for identical twins. Examining each twin's DNA will reveal whether they are identical or fraternal; fraternals also normally have separate amniotic sacs, as well as separate placentas.
Barring pregnancies that result from assisted reproductive technology, dizygotic twins are far more common than monozygotic twins and account for 70 percent of all twin gestations.
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.
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.
Once the babies are large enough to stay in one position in the womb, the twin lowest in the uterus is known as Baby A and the one furthest from there is Baby B, according to the Stanford Medicine News Center. In the majority of vaginal births, Baby A is born first.
Vanishing twin syndrome was first recognized in 1945. This occurs when a twin or multiple disappears in the uterus during pregnancy as a result of a miscarriage of one twin or multiple. The fetal tissue is absorbed by the other twin, multiple, placenta or the mother. This gives the appearance of a “vanishing twin.”