Britannica
Sources used in this answer
Why do identical twins not always have exactly the same traits?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
heredity
Each offspring is a combination of its two parents, receiving some dominant traits from its mother and others from its father.
While identical twins originate from the same fertilized egg and share the same hereditary material, they do not always exhibit identical traits due to several biological and environmental factors.
- Environmental Influence: The expression of a genotype can be modified by the environment. Factors such as nutrition, lifestyle, and exposure to different external conditions can lead to variations in quantitative traits like body weight and intelligence.12
- Epigenetic Modifications: These are chemical modifications to DNA or associated proteins that determine how genes are expressed. Epigenetic changes can occur throughout an individual's life and are often influenced by environmental factors, which can lead to differences in aging rates and disease susceptibility between identical twins.3
- Genetic Processes: Although identical twins start with the same genetic code, developmental and genetic differences can arise through processes such as somatic mutation, where genetic alterations occur in a cell after the initial zygote has split. These mutations are then passed on to the progeny of that specific cell.45
Ultimately, the interplay between an individual's unique genotype and their specific environmental experiences ensures that even genetically identical individuals can develop distinct characteristics.21