Functional Genomics, Epigenetics, and Three-Dimensional Genome Organization
Beyond sequence: regulated genomes in space and time
Chromatin and epigenetic state
Epigenetic information refers to heritable or semi-stable changes in gene regulation that do not alter DNA sequence. Histone modifications, DNA methylation, nucleosome positioning, and nuclear localization contribute to cell identity and developmental memory.
3D genome concepts
Why 3D genome organization matters
Regulatory elements can act over tens or hundreds of kilobases, and sometimes over much larger distances through looping and nuclear positioning. Structural variants may therefore produce phenotype by rewiring regulatory neighborhoods rather than disrupting coding sequence directly.
Important distinction
Epigenetic states can be stable across cell divisions without being permanently inherited across generations. Cellular memory and transgenerational inheritance are related but not identical phenomena.
Sequence change versus epigenetic change
DNA sequence change
- Alters the nucleotide code
- Usually stable across cell divisions and generations
- Detected by sequencing
Epigenetic change
- Alters regulatory state without changing sequence
- Often dynamic and context-dependent
- Detected by chromatin and methylation assays
Which observation most strongly suggests a regulatory rather than coding mechanism?
A distal enhancer variant is a classic regulatory mechanism affecting expression rather than protein sequence.
Correct answer: A phenotype is caused by a variant in a distal enhancer
What is one reason structural variants can have large phenotypic effects?
Large-scale rearrangements often perturb more than a single coding change would.
Correct answer: They can disrupt gene dosage, break genes, or rewire long-range regulatory interactions within the 3D genome.
From chromatin mark to phenotype
-
1
A chromatin feature changes accessibility or polymerase recruitment.
-
2
Expression of target genes shifts in a cell-type-specific manner.
-
3
Cell state, differentiation, or signaling output changes.
-
4
The altered cellular program contributes to organismal phenotype.
Which assay is most directly used to measure chromatin contacts?
Hi-C captures genome-wide chromatin contact frequencies.
Correct answer: Hi-C