Epigenetic tag removal resets many parental methylation patterns after fertilization, allowing early developmental genes to be expressed in embryos and tissues.
Coverage 2016–2023 · Updated 16 Jul 2026
During human egg and sperm development, most epigenetic tags are removed, but retained imprints can make only the maternal or paternal copy of a gene active in offspring.
Resetting prevents most acquired expression states being passed between generations. For an imprinted gene, a retained parent-specific tag silences one allele, so phenotype depends on whether the active copy came from the mother or father.
| Hybrid cross | Epigenetic growth outcome |
|---|---|
| Male tiger × female lion → tigon | Tiger paternal genes lack the lion's strong growth promotion, while the lioness contributes anti-growth imprinting; the hybrid is about parental size or smaller |
| Male lion × female tiger → liger | Lion paternal growth promotion is not opposed by the tigress's imprints in the same way; the hybrid can grow larger than either parent |
The hybrid pattern supports a parent-of-origin epigenetic explanation, but the exact imprinted genes making the largest growth difference are not established in the approved local textbook.
This objective is assessed through multiple choice.
Some marks, such as imprints, may be retained in specific cases and can affect offspring phenotypes.
Representative question
Very soon after fertilization, parental epigenetic methylation is reversed in the DNA. Later, tissue-specific epigenetic modifications are made to the embryonic DNA. The graph follows the degree of methylation from different sources during embryonic development.
According to the graph, what are the changes in DNA methylation during embryonic development?
Only the paternal DNA becomes demethylated.
The maternal DNA becomes demethylated first.
The methylation patterns of the parents' DNA are erased before fertilization.
The methylation patterns of both parents are erased after fertilization.
