Q. What are twins? Genetically what are the two types of twins that can be generated?
Twins are at the same time generated (within the mother's uterus) offspring. Twins classify according to zygosity as dizygotic or as monozygotic twins.
Monozygotic twins, also called as identical twins are those originated from one single fertilized ovum (therefore from one single zygote) and monozygotic twins are genetically identical that is they have identical genotypes and are necessarily of the same sex. Dizygotic twins also called as fraternal twins are those generated from two different ova fecundated by two different sperm cells and so they are not genetically identical and they are not necessarily of the same sex.