Congenial twins are "dizygotic," meaning that they developed from 2 unlike eggs fertilized by 2 different sperm cells, while identical twins are "monozygotic" i.due east., they adult from a unmarried fertilized egg that divide. The likelihood of identical twins is the same effectually the earth — about three in 1,000, while the incidence of fraternal twins varies by geography and ranges from half-dozen to over 20 per one,000 deliveries.

Comparison chart

Fraternal Twins versus Identical Twins comparison chart
Edit this comparison chart Fraternal Twins Identical Twins
Develop from Two unlike eggs fertilized by two different sperm cells The splitting of the same fertilized egg into ii
Genetic code Like whatever other sibling; not identical. Nearly identical
Gender Ordinarily different Always the same
Likelihood Varies past land. About half dozen in 1,000 in Japan, up to over xx per 1,000 in some parts of Africa. Ii-thirds of all twins in the earth are fraternal. Compatible around the earth; about 3 in 1,000. Only 1-third of all twins in the world are identical.
Blood type May be different Ever the same
Causes Hereditary predisposition, certain fertility drugs, IVF Not known
Advent As similar equally whatever other sibling Extremely like, although may not be exactly identical due to environmental factors
In utero Develop carve up sacs in utero. May exist contained in i sac in utero.
Risk for TTTS (twin-to-twin transfusion syndrome) Low risk Higher risk compared with congenial twins
Fingerprints Different Different

Zygosity and Genetic Similarity

Zygosity of fraternal and identical twins.

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Zygosity of congenial and identical twins.

Zygosity refers to the similarity between the genomes of each twin. Congenial twins are dizygotic, significant that they developed from 2 unlike eggs fertilized past two different sperms. Their genetic lawmaking is equally like (or unlike) as any other siblings.

Identical twins are monozygotic, pregnant that they developed from the aforementioned fertilized egg, and so have nearly identical genetic lawmaking. They almost always take the same gender and many of the aforementioned concrete characteristics (phenotypes). However, they may develop some genetic differences later the zygote splits, due to mutations in the DNA.

Children of monozygotic twins exam genetically as one-half-siblings instead of first cousins.

Types

There are four types of twins:

  • Diochorionic-diamniotic twins either never divided (aka are fraternal twins) or divided within the starting time four days and have two separate amniotic sacs and placentas. This includes almost all fraternal twins.
  • Monochorionic-diamniotic twins share the same placenta, merely have 2 amniotic sacs. This occurs when the embryo splits in 4-8 days and includes 60-seventy% of all identical twin pregnancies.
  • Monochorionic-monoamniotic twins share the aforementioned amniotic sac and appear when the embryo splits after nine days.
  • Conjoined twins occur when segmentation takes identify later than 12 days subsequently fertilization.

Identifying congenial and identical twins

Oftentimes, identical twins can exist identified in the womb, equally they ofttimes share a placenta. Subsequently nascence, it can be deduced that twins are congenial if they are of different genders (a boy and a girl) or if they have different blood types. However, the just way to reliably conclude that they are identical twins is through genetic testing (a twin zygosity Deoxyribonucleic acid exam).

Quite paradoxically, identical twins may not always look exactly alike fifty-fifty though they share the same genetic make up. Environmental factors may crusade their appearance to evolve differently equally early as within the mother'due south womb. Hither'due south a video of twin children of an interracial couple, i of whom is blackness and the other white:

Risks

The survival charge per unit of monoamniotic twins is betwixt 50-60%, considering of the chance that the umbilical string will get tangled around the babies. This can as well deprive them of oxygen, leading to cognitive palsy. Twins are at college chance of lower nascency weights and premature birth. The length of gestation is usually around 38 weeks for twins, compared to 40 for single births.

Statistics

The gamble of identical twins is the same all over the world: around 3 in every 1000 births.

The chance of congenial twins depends on many factors, include the land of birth (they course half-dozen out of every 1000 births in Japan, to 15 or more per grand births in parts of Republic of india). They are more common in mothers over 35, and in pregnancies that involve IVF treatment.

Fraternal twins occur due to hyper-ovulation i.e. the female parent releasing more than i egg per cycle. Women who have already had fraternal twins are four times more than likely to have fraternal twins in their next pregnancy. Certain drugs similar clomiphene increment the probability of fraternal twins to near 10% because they tend to bring nearly hyper-ovulation. [1]

Fingerprints

Neither fraternal nor identical twins have the same fingerprints. This is considering ecology factors in the womb affect the development of fingerprints, slightly altering them for each individual. Fingerprints are an instance of phenotype, which tin exist different even if two individuals share the same genotype.

References

  • Wikipedia: Twin
  • Twin Zygosity - Near.com Multiples
  • Why don't identical twins accept identical fingerprints?
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