There is weak evidence that monozygotic twins sharing a placenta have a higher concordance rate for schizophrenia than monozygotic twins with separate placentas.
32.
Non-conjoined monozygotic twins form up to day 14 of embryonic development, but when twinning occurs after 14 days, the twins will likely be conjoined.
33.
A study of 80 pairs of monozygotic twins ranging in age from three to 74 showed that the youngest twins have relatively few epigenetic differences.
34.
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.
35.
In monozygotic twins the impact of genotypes ( i . e . factors ( 1 ) and ( 2 ) is much stronger than in dizygotic twins.
36.
Monochorionic twins occur in 0.3 % of all pregnancies . 75 % of monozygotic twin pregnancies are monochorionic; the remaining 25 % are " dichorionic diamniotic ".
37.
The fact that even monozygotic twins don't share a 100 % concordance rate suggests environmental factors play a role in the vulnerability and development of the disorder.
38.
Gringas and Chen ( 2001 ) describe a number of mechanisms which can lead to differences between monozygotic twins, the most relevant here being chorionicity and amniocity.
39.
As for asexual reproduction, the only thing that sort of comes close is the formation of monozygotic twins, which occurs at the fertilised oocyte stage, not later.
40.
Another issue is the recent finding that even monozygotic twins can be different and there is a mechanism which might account for monozygotic twins being discordant for homosexuality.
