Twins that share a single placenta.

Concordance rates that suggested a role of genes in schizophrenia might more accurately be interpreted as a reflection of the influence of shared prenatal experience.

With identical twins, one egg (zygote) from the mother is fertilized by one sperm from the father, and then very early in development the embryo splits and two fetuses grow. Spontaneous division of the zygote into two embryos is not considered to be a hereditary trait, but rather a spontaneous or random event.

If the zygote splits very early (in the first 2 days after fertilization) they may develop separate placentas (chorion) and separate sacs (amnion). These are called dichorionic, diamniotic (or 'di/di') twins. While all fraternal twins are 'di/di', this occurs 20 - 30% of the time in identical twins.

Most of the time in identical twins the zygote will split after 2 days, resulting in a shared placenta, but two separate sacs. These are called monochorionic, diamniotic ('mono/di') twins.These twins are very similar genetically, and share a single afterbirth.

Very occasionally, twins will also share the same sac (fluid cavity). In about 1% of identical twins the splitting occurs late enough to result in both a shared placenta and a shared sac. These are called monochorionic, monoamniotic ('mono/mono') twins.

Evil Twins - 2012 Gibbons Twins 1-12 was released on:

USA: 6 August 2013

Identical twins are formed by the separation of the same embryo containing same genetic coding. thus the the twins are identical as formed from the same embryo.

But this is not the case in the non-identical twins as they are formed from the individual embro each having different genetic coding.