D2.2.4 (HL)—Epigenesis

Epigenesis produces differentiated cell states by changing gene activity patterns without altering the underlying DNA base sequence during development processes.

Epigenesis is the development of patterns of cell differentiation in a multicellular organism from an initially undifferentiated zygote.

Cells descended from the zygote usually contain the same DNA sequence, but different genes become active or repressed. Epigenetic changes such as DNA methylation or histone modification alter how genes are read without altering their base sequences.

One zygote → repeated cell division → different epigenetic states and gene-expression patterns → different proteins → specialized cell phenotypes.

A developing muscle cell activates genes for contractile proteins while maintaining repression of genes needed only in neurons, producing differentiation without changing genotype.

Epigenetic change can alter phenotype but not genotype because the nucleotide sequence remains unchanged. It is therefore not a gene mutation.

Transcription factors, promoters, enhancers, activators and repressors control RNA polymerase activity.
mRNA lifetime limits translation; poly-A shortening and nucleases help remove transcripts.
DNA methylation and histone modification alter chromatin access without changing base sequence, creating epigenetic patterns during differentiation.
The genome is all genetic information; the transcriptome and proteome vary with cell type, time and environment.
Some epigenetic marks persist through cell division or inheritance, although most are reset during gamete formation; genomic imprinting is an exception.
Hormones regulate eukaryotic transcription through receptors and transcription factors; lac and trp operons illustrate bacterial control.
Twin studies and environmental exposures help separate genetic, epigenetic and environmental effects on phenotype.

Concept essentials

Differentiated cells can contain the same genome but express different genes.
Epigenesis creates stable patterns of gene activity during development.
Epigenetic regulation does not require a DNA base-sequence change.
Cell type depends on which genes are active or inactive.

D2.2.4 (HL)—Epigenesis

Epigenesis Builds Differentiated Cell Patterns

HL Gene Expression Control

Concept essentials