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Updated: May 7, 2026
17:14
Chromosome Replicating Timing Combined with Fluorescent In situ Hybridization
Published on: December 10, 2012
Random replication of the inactive X chromosome.
Amnon Koren1, Steven A McCarroll
1Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA;
Genome Research
|September 26, 2013
Summary
DNA replication in eukaryotic cells follows two distinct strategies: slow, ordered replication for active genes and rapid, random replication for silent chromatin like the inactive X chromosome (Xi). These processes are spatially and temporally segregated within the cell.
Area of Science:
- Cellular and Molecular Biology
- Genetics
- Epigenetics
Background:
- Genomic DNA replication in eukaryotes occurs in an ordered temporal sequence.
- The inactive X chromosome (Xi), a large block of facultative heterochromatin, replicates later than the active X chromosome (Xa).
- Replication dynamics of inactive chromatin remain largely unknown.
Purpose of the Study:
- To profile human DNA replication timing in an allele-specific and chromosomally phased manner.
- To separately determine replication timing for the active (Xa) and inactive (Xi) X chromosomes.
- To elucidate the replication dynamics of inactive chromatin.
Main Methods:
- Allele-specific DNA replication profiling.
- Chromosomally phased analysis.
- Human cell studies.
Main Results:
- Replication timing of the Xi differs significantly from the Xa and shows inter-individual variation.
- Xi replication appears rapid and unstructured, distinct from euchromatic regions.
- Late-replicating autosomal regions also exhibit unstructured replication, similar to the Xi.
Conclusions:
- DNA replication employs two main strategies: slow, ordered replication for transcriptionally active regions and rapid, random replication for silent chromatin.
- These two replication strategies coexist within the same cell but are segregated in space and time.
- The Xi exemplifies rapid, random replication characteristic of silent chromatin.
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