IB Biology Topic D2.2.8: Examples of Environmental Effects on Gene Expression in Cells and Organisms Notes

Air Pollution Changes DNA Methylation and So Alters Gene Expression

1. Air pollution, especially fine particulate matter (PM2.5) and gases like nitrogen dioxide (NO₂), alters DNA methylation patterns.
2. Exposure triggers oxidative stress and inflammation, which drive epigenetic changes in key genes.

Pollution Silences Tumour-Suppressor Genes and Activates Inflammatory Genes

1. Hypermethylation of tumour-suppressor genes silences their expression.
   1. This raises the risk of cancers such as lung cancer.
2. Hypomethylation of pro-inflammatory genes activates pathways that produce cytokines.
   1. People exposed to high PM2.5 show increased activity in genes linked to chronic inflammation.
   2. This is a precursor to cardiovascular and respiratory diseases.

Diet, Stress, and Temperature Also Reshape Methylation

1. Diet
   1. A diet rich in folate enhances DNA methylation, supporting normal development.
   2. Folate deficiency reduces methylation and can lead to neural tube defects in fetal development.
2. Stress
   1. Chronic stress reduces methylation of the stress-hormone receptor gene, leading to heightened stress responses.
   2. This has been observed in people who experienced trauma during childhood.
3. Temperature
   1. In some reptiles, incubation temperature affects methylation of sex-determining genes.
   2. This influences whether the offspring develops as male or female.

Some Changes Are Temporary, Others Persist and Can Reach Offspring

1. Short-term adaptation: reversible changes let organisms adjust to their immediate environment.
2. Long-term risks: lasting exposure can lock in harmful changes, raising the risk of cancer, asthma, and cardiovascular disease.

Persistent Tags and Inheritance

1. Some DNA methylation patterns survive meiosis and are passed to offspring.
2. Through this epigenetic inheritance, offspring can in effect inherit a record of conditions their parents met.