There are two major ways in which twinning can result. These two ways are what gives rise to the terms, identical and non-identical twins.
For the non-identical twins, a woman produces two eggs which are each fertilized differently by different sperm from the man. Each of these fertilized eggs then continues to grow into a separate baby.
Since each of these babies started with a different egg and sperm, they have different DNA. This type of twinning is regarded as non-identical or fraternal twinning.
Each of them is just like every other person just that they shared the same womb and are born at the same time.
For the identical twins, the mother produces only one egg and it is fertilized by only one sperm. Normally this fertilized egg should continue to grow and form only one baby.
However, for reasons still being researched the fertilized egg can split into two and each half of the division continues to grow separately each into a baby.
So, the two babies are produced from one egg that is fertilized by one sperm. The babies produced by this union are known as monozygotic twins or identical twins.
A common question often asked is whether identical twins have the same deoxyribonucleic acid, DNA.
What Is DNA?
Deoxyribonucleic acid is a molecule composed of two chains that coil around each other to form a double helix carrying the genetic instructions used in the growth, development, functioning, and reproduction of all known organisms.
The genetic information in the DNA determines everything about humans, from our physical appearance as well as personality traits.
A Look At Monozygotic Twins
“Monozygotic twins” is the medical term for identical twins. Mono refers to one while zygote means a cell that’s formed by the fertilization of a human egg by the sperm.
So, identical twins are created when a single zygote splits into two. These two entities, each continue to divide and grow. This process is technically considered a malfunction of the normal process of development.
The two separate babies formed in this way share the same DNA, however, they aren’t exactly alike. That’s why every mother can tell her identical twin babies apart because each of them develops separately, and lives a separate life.
Are Identical Twins Completely Identical?
They are not completely identical because the DNA is essentially like instructions for building the body, how each person builds that is different. It explains why identical twins have similar, but not identical fingerprints.
A lot of factors play a role in the appearance and behavior of every person, including identical twins. The environment in which each one is raised can influence a person’s physical appearance and personality.
Furthermore, as twins grow, epigenetic factors create differences between them. The epigenome describes chemical changes within DNA as individual ages.
Hence, identical twins can have different temperament, appearance, and personality.
How To Determine If Twins Are Identical?
The chances of having identical twins are about 3 in 1,000 and about one-third of all twins are monozygotic. The majority of twins are fraternal, produced when two separate sperm fertilize two different eggs.
The only way to find out if a pair of twins are identical is to perform a DNA test. DNA testing is carried out on the two people. Collecting DNA sample is quick and painless. The sample is obtained by swabbing the inside of each twin’s cheek, and then the samples are sent for analysis.
Thereafter, the DNA results from each individual are compared. If they are monozygotic twins, the DNA test result will be 99.99 percent similar. However, a DNA test result from non-identical twins will generally be about 50 percent to 75 percent similar.
Can Identical Twins Get Away With Crime?
Because identical twins have similar DNA, it may be nearly impossible to distinguish between these individuals when analyzing DNA in crime situations.
However, a more old-fashioned model in crime investigation actually can be used to distinguish between twins. Fingerprint evidence can help identify the criminal, even if they are identical twins. That’s because even identical twins have unique fingerprints. So, identical twin may not be able to get away with a crime.
Identical twins are formed from the splitting of a zygote formed from one egg and one sperm. Although they share similar DNA, it is not completely the same. The only way to identify if a pair is identical twins is to carry out DNA testing on the two of them.
Guest article by Dr Charles-Davies, a medical doctor at Brookside Medical Practice, a clinic in Lagos that specializes in family medicine and DNA testing.