Blood groups are a type of classification that is based on the presence or absence of antibodies present on the red blood cell.
The most common is the ABO blood group.
Based on these criteria four major types of blood group exists that are A, B, AB and O.
Twins
It refers to two offspring that are given birth during the same pregnancy.
These twins can be either physiologically and genetically the same or different.
Twins that are born when a single fertilized zygote splits giving rise to another identical zygote are called identical or monozygotic twins.
In some cases, there may be two sperms fertilizing two different ova at the same time giving rise to two developing zygotes, these are called fraternal or dizygotic twins.
Identical twins have the same blood type while non-identical or fraternal twins may or may not have the same blood group.
Monozygotic twins or identical twins are formed from the same zygote so they have similar physiological and genetic features.
Fraternal or dizygotic twins are formed by two different fertilization resulting in two different zygotes.
Thus, fertilization may occur with different constituents of genetic material from both parents resulting in physiologically different twins.
