Most Tags Are Erased in Gametes, But a Few Persist as Genomic Imprints
During the formation of gametes, most epigenetic tags are erased to give the next generation a clean slate.
These tags, such as DNA methylation and histone modification, change gene expression without altering the DNA sequence.
A small fraction of tags are not erased, leading to genomic imprinting, where certain genes are silenced depending on which parent they came from.
Definition
Genomic imprinting
Genomic imprinting is a form of epigenetic inheritance, where the expression of a gene depends on whether it is inherited from the mother or the father.
Note
Imprinted genes are expressed from only one parent's copy, while the other copy stays silenced.
This is why some inherited effects depend on whether a gene came from the mother or the father.
Persistent Tags Regulate Genes for Growth, Development, and Metabolism
Surviving tags ensure that imprinted genes are expressed in a parent-specific way.
Many imprinted genes control growth, development, and metabolism.
The differences between ligers and tigons show how imprinted tags from each parent shape offspring.
Lions: paternal genes promote growth, since males compete to sire the largest cubs.
Tigers: maternal genes limit growth to conserve the resources of a female raising cubs alone.
Analogy
Genomic imprinting works like a tug-of-war between the parents' genes.
In ligers, the lion father's growth-promoting genes win, producing a very large animal.
In tigons, the tiger mother's genes balance the effect, giving a smaller animal.
Why Imprinting Matters for Inheritance
Because imprints escape erasure, they are passed to offspring and produce parent-of-origin effects.
This explains inheritance patterns that ordinary Mendelian genetics cannot.
Active recall
What happens to most epigenetic tags during gamete formation?
Define genomic imprinting.
Name three processes commonly controlled by imprinted genes.
Why is a liger larger than a tigon in terms of parental imprinting?
