are identical twins genetically identical
Fraternal twins are “dizygotic,” meaning that they developed from two different eggs fertilized by two different sperm cells, while identical twins are “monozygotic” i.e., they developed from a single fertilized egg that split. Identical, or monozygotic, twins develop from a single egg/sperm combination that splits a few days after conception. Their DNA originates from a single source, thus their genetic makeup is the same and the characteristics that are determined by genetics will be similar. While identical twins form with the same set of genes, human development is not just genetic. The environment also has an impact. So, beginning in the early environment of the womb, external influences can change the appearance of twins. For example, some monozygotic twins share a placenta. Twins are two offspring produced by the same pregnancy. Twins can be either monozygotic (identical), meaning that they develop from one zygote, which splits and forms two embryos, or dizygotic (fraternal), meaning that they develop from two different eggs. In fraternal twins, each twin is fertilized by its own sperm cell. The Claim: Identical Twins Have Identical DNA. It is a basic tenet of human biology, taught in grade schools everywhere: Identical come from the same fertilized egg and, thus, share identical genetic profiles. But according to new research, though identical twins share very similar genes, identical they are not. The discovery opens a new understanding of why two people who hail from the same embryo can differ in phenotype, as biologists refer to a person’s physical manifestation. Zygosity of fraternal and identical twins. Zygosity refers to the similarity between the genomes of each twin. Fraternal twins are dizygotic, meaning that they developed from two different eggs fertilized by two different sperms. Their genetic code is as similar (or dissimilar) as any other siblings. Identical twins are monozygotic, meaning that they developed from the same fertilized egg, and so have nearly identical genetic code. They almost always have the same gender and many of the same physical characteristics (phenotypes). After birth, it can be deduced that twins are fraternal if they are of different genders (a boy and a girl) or if they have different blood types. However, the only way to reliably conclude that they are identical twins is through genetic testing (a twin zygosity DNA test). Monozygotic twins, although genetically very similar, are not genetically exactly the same. The DNA in white blood cells of 66 pairs of monozygotic twins was analyzed for 506,786 single nucleotide polymorphisms known to occur in human populations. The stereotype of identical twins is that they are exactly the same: they look alike, they dress in matching outfits, they share the same likes and disklikes. Parents of identical twins know differently, however. Despite their shared genetic component, identical multiples are unique individuals. Though they do share similarities, they also have many differences. For example, my own children have always exhibited about a twenty-five percent difference in their weight. Comparison of zygote development in monozygotic and dizygotic twins. In the uterus, a majority of monozygotic twins (60–70%) share the same placenta but have separate amniotic sacs. In 18–30% of monozygotic twins each fetus has a separate placenta and a separate amniotic sac.
Yes, they have nearly identical genetic code.