Investigating the Human Genome: Insights into Human Variation and Disease Susceptibility

4. Gene-environment interactions

In many genetic disorders, evidence indicates that individuals who carry the same mutation in the same gene do not necessarily have the same disease manifestations. This is true even in families that harbor the same mutation. One question that arises is to what extent modifier genes influence expression. Another important question is whether environmental factors, internal or external, interact with specific gene mutations and alter their impact. Penetrance of a specific allele that impacts the phenotype is defined as the probability that an individual who carries that allele will manifest the corresponding phenotype.

Evidence also indicates that individuals with mutations in a specific gene occur more frequently ...