Helan Thomas
Andrea Herrera
Have you ever wondered why some identical twins look exactly alike while others grow more different over time? Twins are not just intriguing; they are invaluable to genetic research. Because identical twins share the same DNA, scientists can study how genes and the environment interact by observing them over time. Similarly, families share genes to different degrees, and both help better understand various conditions.
In this blog, we are going to talk about the types of twins, the percentage of family genes shared, the role of environmental factors in our genes ( and how twins help discover these), and previous twin studies and their impact on research and application in medical practice.
How are genes inherited in families?
The amount of DNA you share with family members varies depending on how closely related you are. You share about 50% of your DNA with each parent and with your full siblings. It drops to roughly 25% with your grandparents and with your aunts and uncles, who are your parents’ siblings. You share around 12.5% with your first cousins and with your great-grandparents, and only about 3% with your second cousins. In the case of twins, however, the amount of shared DNA can be much higher—up to 100% in identical twins.
Types of Twins
To understand twin studies, it is essential to understand the basics. When a baby is conceived, one egg meets one sperm (fertilized egg). The two most common ways to end up with a twin:
Identical twins (monozygotic twins): a single egg and sperm combination splits into two embryos, meaning the twins share 100% of the same DNA. They’re essentially natural clones of each other, which makes them incredibly valuable for genetic research.
Fraternal (dizygotic twins): two separate eggs fertilized by two separate sperm. Genetically, they’re like any other siblings, sharing about 50% of their DNA—but they grow up side-by-side in the same womb and environment.
Understanding the difference between identical and fraternal twins helps scientists better tease apart which traits are inherited and which are influenced by environment, showing how these insights advance health research and treatments.
Why are twins so crucial for genetic studies?
When studying identical twins, any differences between them are most likely due to environmental factors, since their genes are similar. Fraternal twins, on the other hand, share both some of the same genes and the same environment, allowing scientists to see the effects of both.
Epigenetics: what makes twins different
Epigenetics is the study of how life factors—like diet, stress, toxin exposure, or lifestyle—can influence gene expression without altering the DNA sequence. Twin studies are also instrumental in estimating heritability or the degree to which genetics explains a trait, and what makes them have some differences between them.
What’s more, scientists are studying how the environment can influence gene expression through epigenetic mechanisms. For example, in cancer research, some therapies—such as HDAC inhibitors—are already used to modify gene expression. Although studies have shown differences in DNA methylation patterns in genes associated with Parkinson’s disease compared with healthy controls, effective treatments that directly target these epigenetic changes are still lacking.
Research studies, including the CCBP study, aim to understand better how genes and environmental factors interact within families to influence the development of Parkinson’s and Alzheimer’s disease, with the ultimate goal of enabling more targeted and effective treatments.
Remarkable Twin Study: Stories in the space
Scott Kelly and his identical twin, Mark Kelly, participated in a NASA study to identify gene expression differences between living on Earth and a space environment. Observations included changes in telomere lengths—DNA segments linked to ageing—and shifts in his immune and cognitive functions. Such findings provided NASA with invaluable insights into how extreme environments influence human biology, highlighting the dynamism of genetics.
Conclusion
Twin and family studies offer a powerful window into how health and disease develop over time. By comparing people who share different amounts of DNA—especially identical twins who share the same genetic code—researchers can better understand how genes and environmental factors interact to influence conditions like Parkinson’s and Alzheimer’s. These studies show that while we inherit genetic risk, our environment, lifestyle, and life experiences play a critical role in shaping how those genes are expressed. Research programs such as the CCBP study use family- and twin-based approaches to uncover these complex interactions, aiming to improve early diagnosis, guide prevention strategies, and develop more personalized and effective treatments. Understanding health through families does not just benefit research—it helps future generations.
FAQ
What is a twin study?
A twin study is a type of research that compares identical and fraternal twins to understand how much of a trait or disease is influenced by genetics versus environmental factors.
Why are identical twins so crucial for research?
Identical twins share 100% of their DNA. If one twin develops a disease and the other does not, researchers can study environmental and lifestyle factors that may explain the difference.
How do family studies help genetic research?
Family members share different percentages of DNA. Studying families helps researchers track how genetic risk and environmental exposure are passed across generations.
What role does epigenetics play in disease?
Epigenetics explains how factors such as diet, stress, toxins, and lifestyle can alter gene expression without altering the DNA itself.
Can twin studies help improve treatments for Parkinson’s and Alzheimer’s disease?
Yes. Twin and family studies help identify risk factors, disease mechanisms, and potential targets for more personalized and effective treatments.
Do I need to be a twin to participate in research studies?
No. Many studies, including CCBP, welcome families and individuals, not only twins, because shared family information is equally valuable.
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