Dizygotic twins, like any other siblings, have an extremely small chance of having the exact same chromosome profile. Like any other siblings, fraternal twins may look very similar, particularly given that they are the same age. However, fraternal twins may also look very different from each other. They may be a different sex or the same sex. The same holds true for brothers and sisters from the same parents, meaning that fraternal twins are simply brothers and/or sisters who happen to have the same age.
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Knowledge CornerTwins are formed when either one fertilized egg splits into two or two eggs get fertilized at the same time, producing one pregnancy, but two babies. There are two main categories of multiples—Fraternal and Identical. Similarity in looks does NOT determine whether twins are identical versus fraternal. Identical, or Monozygotic Twins occur when a single fertilized egg splits into two embryos around the time the fertilized egg is becoming implanted in the womb (usually between the fourth and 12th day after fertilization). Monozygotic twins make up 1/3rd of all twins. The two embryos develop into fetuses sharing the same womb. When one egg is fertilized by one sperm cell, and then divides and separates, two identical cells will result. If the zygote splits very early (in the first 2 days after fertilization) they may develop separate placentas and separate sacs . In about 1% of identical twins the splitting occurs late enough to result in both a shared placenta and a shared sac. Finally, the zygote may split extremely late, resulting in conjoined twins.Fraternal Or Dizygotic Twins are the result of two separate eggs (ovum) becoming fertilized by two separate sperm, resulting in two completely distinct pregnancies in the womb at the same time. They are known as non-identical or dizygotic twins. Dizygotic twins account for about 2/3rds of all twins.
Mirror twinsSome monozygotic twins are known as "mirror twins" or mirror image twins. These are identical twins with opposite features, that is, one may be right-handed and the other left, mirrored hair curls, etc. This condition is comparatively rare in humans: about 25% of all identical twins are mirrored to some degree, but in the vast majority of these cases it is a very minor feature - such as mirrored finger prints. Mirroring results from a late split of the fertilized egg at around 9-12 days. One mirror may have sius invtersus, where some or all of the organs are on the opposite side of the body, such as the left ventricle of the heart on the right (dextrocardia). Such conditions are usually associated with a higher incidence of other birth defects, and are very rare. Conjoined TwinsConjoined twins (or "Siamese twins") are monozygotic twins whose bodies are joined together at birth. This occurs where the single zygote of identical twins fails to separate completely, and the zygote starts to split after day 13 following fertilization. This condition occurs in about 1 in 50,000 human pregnancies. Most conjoined twins are now evaluated for surgery to attempt to separate them into separate functional bodies. The degree of difficulty rises if a vital organ or structure is shared between twins, such as brain, heart or liver. Want to learn more >> learn more Still some questions in mind? (*Source Wikipedia)
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