Epigenetics and Transgenerational Effects of the Environment

What is epigenetics?

The study of heritable changes in gene expression that do not involve changes to the DNA sequence.

How do promoter regions influence gene expression?

Promoters are regulatory regions upstream of genes that control whether transcription begins — their accessibility determines if a gene is "on" or "off."

How does histone wrapping affect gene expression?

DNA wraps around histones; tightly coiled regions are less accessible to transcription machinery, reducing gene expression.

What is DNA methylation?

The addition of methyl groups to DNA (typically cytosine bases), often silencing gene expression by tightening chromatin.

What is acetylation in gene regulation?

Acetyl groups loosen chromatin structure, increasing gene accessibility and promoting transcription.

Does methylation always suppress genes?

Usually, but not always — some methylation can upregulate genes depending on location and context.

How is methylation involved in development?

It regulates which genes are expressed in which tissues, ensuring the same genome produces different cell types.

Can methylation be inherited?

Most methylation is reset during embryogenesis, but some modifications escape reprogramming and are passed through the germline.

What is the Agouti gene example?

In mice, a dominant Agouti mutation causes obesity and yellow fur, but dietary methyl donors in pregnant mothers suppress this effect in offspring.

How does maternal diet affect Agouti offspring?

Increased methylation from supplements silences the Agouti mutation, resulting in healthy, brown-furred pups — despite identical DNA.

What is the key insight from the Agouti experiment?

Environmental input (diet) can override genetic mutations via epigenetic modulation — showing gene-environment interaction.

What effect did sleep deprivation have in rats?

Sleep-deprived rats had lower DNA methylation, leading to reduced control over gene expression and long-term stress effects.

What is the RB group in the rat study?

Rats that were sleep deprived but later allowed recovery — they still showed some methylation changes, indicating lasting effects.

What genes were altered by sleep deprivation?

Glucocorticoid receptor (GR) expression was suppressed, impairing the rats' ability to regulate adrenaline and stress.

How can methylation of GR genes be reversed?

By postnatal experiences — nurturing maternal behaviours (e.g., grooming) can demethylate GR promoter regions, restoring normal stress regulation.

What does the rat GR study suggest about inheritance?

Behaviour (not just genes) can alter methylation patterns in ways that persist across development — an example of epigenetic inheritance without mutation.

What epigenetic effect was observed in Icelandic fish?

Grandparental origin (warm vs cold lakes) influenced body shape in offspring — despite identical rearing conditions.

How does this fish study show transgenerational epigenetics?

The environment experienced by earlier generations altered development in future generations without DNA changes.

Why do warm lake fish have altered body shape?

Due to increased metabolic demands, they evolve structures to better scrape high-energy prey from lake floors.

What does this imply about developmental plasticity?

Environmental pressures can canalise epigenetic patterns that persist across generations — shaping morphology and function.

How is methylation used to measure biological age?

Specific methylation markers can estimate age to within 2-3 days in organisms like Daphnia — more precise than telomere length.

Why are telomeres less accurate for age prediction?

They offer a ~6-month window of precision, while methylation reflects real-time changes to developmental and physiological state.

What link has been found between education level and methylation?

Studies (e.g., in Glasgow) show associations between lower education and altered methylation patterns — suggesting social environment shapes gene expression.