What Are Identical Twins? 

Identical twins are two genetically identical siblings that arise from one fertilized egg, also known as a monozygotic twin. They have the same genotype and look alike, though slight differences do occur due to different development environments in the wombs. Identical twins are not necessarily born at the same time; they may come into existence at different times and have unique birthdays.

What Genomic Differences Are Found In Identical Twins?

While identical twins are genetically alike, they tend to display differences in their epigenomes. Epigenetics is the study of gene expression modifications, which are largely caused by environmental factors. These modifications can change gene expression without affecting the DNA sequence.

  1. Genomic Imprinting
    A major epigenetic difference between identical twins is genomic imprinting. Genomic imprinting is a phenomenon where certain genes can become uniquely modified. This occurs in such a way that the gene is expressed differently when inherited from the mother versus the father. In identical twins, if a gene is imprinted in one twin but not the other, it may still lead to disparities in the final epigenetic landscape.

  2. DNA Methylation Differences
    Epigenetic changes tend to accumulate during a person’s lifetime, and may be passed down from generation to generation. These changes sometimes cause discrepancies in the epigenetic makeup of identical twins. DNA methylation is an important epigenetic process where methyl groups are added to the DNA molecule, which can influence gene expression patterns. As twins age, differences in their methylation patterns can accumulate leading to diverse gene expression profiles.

  3. Differential X Chromosome Inactivation
    Differential X chromosome inactivation (DXCI) is an epigenetic phenomenon in which Barr bodies happen differentially in female identical twins. This rearrangement of the X chromosome has been studied and is thought to result from a random process that leads to different expression of the genes present on the two X chromosomes. This can result in a variety of differences between female identical twins, such as differences in height, physical characteristics, and behavior.

  4. Altered N-glycosylation
    N-glycosylation of many proteins is driven by an epigenetic form of gene expression and can differ between identical twins. These differences can influence the efficacy of many biological processes and can be quite significant.

Benefits Of Identical Twin Studies

Because identical twins have the same genome structure and can experience similar environmental influences, they are a great resource for scientists to study. Twin studies are used to differentiate between environmental and genetic influences in phenotypes and diseases. These studies provide insight into the workings of a single genome, which can help us further understand how environmental factors can affect the outcome of a genotype.

In addition to providing a better understanding of the genome, twins can also provide important information for medical treatments. Because of their genetic identity, twins are perfect for being used as a control group in clinical trials and genome studies. This helps to ensure that any treatments or modifications to the genome are contributing to positive effects.

Identical twins carry genetic modifications no one else does. Due to the unique ways in which their genomes become marked and modified, they can have different epigenetic landscapes, which creates a variety of disparities between them. Despite these differences, twins are incredibly useful for scientists to study and give us insight into the relationship between environment and genetics in various diseases and conditions. They are also a valuable control group in clinical trials, helping make sure that treatments and modifications are successful and beneficial.