Twins can be identical or fraternal. Identical twins have identical genes because they were conceived from the same egg and sperm. Identical twins are always of the same sex.
Fraternal twins have different genes. They were conceived from different eggs and sperm. Fraternal twins may be of the same sex, or, they may be of different sex. The DNA twin zygosity test determines whether twins are identical or fraternal.
The GENETICA DNA Test™ proves with absolute certainty that twins are fraternal when the DNA alleles of each twin are different. When the DNA alleles of each twin are identical, the probability of identity is calculated. The GENETICA DNA Test™ demonstrates a greater than 99.9% probability of identity in such cases.