The supplied Burton and Greer review separates intergenerational effects from s by asking how many generations are affected and whether the relevant genetic material was directly exposed. In mammals, the review notes that environmental effects persisting for three or more generations through the female line, or two or more through the male line, are commonly described as transgenerational. For comparison across species, the authors treat a one-generation parent-to-offspring effect as intergenerational, effects lasting three or more generations as transgenerational, and two-generation observations on a case-by-case basis.
This distinction prevents a common interpretive error. If an exposed pregnant parent contains both the developing offspring and the offspring's developing germ cells, more than one generation can be directly exposed. Persistence into an unexposed generation provides a stronger basis for a transgenerational claim.
The review also distinguishes transient s from permanent effects. Transient effects persist for several generations and then disappear. Permanent effects can be maintained indefinitely. Duration is therefore part of the phenotype and must be measured rather than assumed.
Mechanisms and interacting carriers
The supplied review identifies small RNAs, histone modifications, and as prominent candidate carriers of non-genetic information. These mechanisms can interact. Small RNAs may direct , histone and DNA modifying enzymes can influence one another, and feedback between pathways can help maintain silencing.
The same review cautions that other carriers and interacting systems may also contribute. Its conclusion mentions inherited proteins, prions, the microbiome, lipids, and other RNAs as mechanisms that either have been investigated or could transmit information. The central lesson is that a phenotype may emerge from a network rather than a single isolated mark.
Resetting remains equally important. The supplied lecture and rewrite describe LSD1 or SPR-5 as an eraser of in germline experiments. When resetting fails, regulatory states can accumulate across generations and disrupt fertility or cell identity. Erasure is therefore not the absence of . It is an active part of epigenetic control.