Concordance = presence of the same trait.
Identical twins have a higher rate than fraternal because most of their DNA is identical, it’s identical because the zygote split into two so the babies shared an amniotic sack. (Zygote is fertilized egg) so the baby got duplicated meaning only one egg and sperm created two babies. Fraternal twins happen when two eggs are fertilized and grow in separate amniotic sacks. So two different babies, two different eggs and sperm.
