Heteroplasmy
Definition
The co-existence of two or more mitochondrial DNA sequence variants within a single individual, arising from somatic mutation or incomplete segregation. Length heteroplasmy (common in HV1 C-stretch) and point heteroplasmy (a two-base mixture at a single position) are both reported in forensic casework.
- Definition
- Two or more different mitochondrial DNA sequences within a single individual
- Main Types
- Point heteroplasmy (mixed base at single position) and length heteroplasmy (overlapping patterns in repeat regions like C-stretch)
- How It Forms
- Somatic mutation and incomplete segregation of mtDNA during cell division
Common questions
What is heteroplasmy in mitochondrial DNA?+
Heteroplasmy is the presence of two or more different mitochondrial DNA sequences within a single individual or tissue. This happens because mitochondria accumulate somatic mutations and don't always segregate their DNA evenly during cell division. It's a normal finding in forensic casework and must be distinguished from sequencing artifacts to avoid false exclusions.
How does heteroplasmy appear in DNA testing?+
Point heteroplasmy shows up as a mixed peak at a single position in Sanger sequencing, meaning two different bases are present at that exact spot. Length heteroplasmy appears as overlapping patterns, especially in the C-stretch regions of HV1 (hypervariable region 1). Both patterns are common in forensic mitochondrial DNA analysis.
Why does heteroplasmy matter in forensic casework?+
Heteroplasmy affects how mitochondrial DNA profiles are interpreted. It can create ambiguity in matching and comparison, so analysts must recognize it to avoid incorrectly excluding a potential source. Understanding whether variation is heteroplasmy or degradation helps ensure accurate conclusions.
Related terms
- rCRS
- The revised Cambridge Reference Sequence (GenBank accession NC_012920), the standard reference for human mitochondrial DNA. All mtDNA variant positions in forensic and...
- AFDIL
- Armed Forces DNA Identification Laboratory, at Dover Air Force Base, Delaware. The US military's central identification laboratory, responsible for mtDNA-based identification of...
- D-Loop
- The non-coding displacement-loop control region of the mitochondrial genome (~bp 16024-576 in the rCRS). Contains the origin of replication and the promoters,...
- EMPOP
- EMPOP mtDNA Population Database, maintained at the Institute of Legal Medicine, Innsbruck, Austria. Contains over 50,000 curated mtDNA sequences and uses phylogenetic...
- Hypervariable Region (HV1, HV2)
- Two segments within the mitochondrial D-loop that accumulate sequence variation faster than the coding mitochondrial genome. HV1 spans positions 16024-16365; HV2 spans...
- Petrous Bone
- The petrous portion of the temporal bone, the densest bone in the human skull. Its dense hydroxyapatite matrix protects enclosed DNA from...
- Protamine
- Small arginine-rich proteins that replace histones in the nuclei of spermatozoa during spermatogenesis, producing a hyper-compacted chromatin structure approximately six times denser...
- RSRS
- Reconstructed Sapiens Reference Sequence (2012). A phylogenetically derived ancestral human mtDNA sequence used in academic population genetics but not in forensic casework...
Explained in these topics
- Mitochondrial DNA Sequencing on HV1/HV2 and the rCRS ReferenceThe presence of two or more different mtDNA sequences within a single individual or tissue. Point heteroplasmy appears as a mixed peak in Sanger sequencing; le...
- The Cell, the Nucleus and the Mitochondrion as DNA ReservoirsThe co-existence of two or more mitochondrial DNA sequence variants within a single individual, arising from somatic mutation or incomplete segregation. Length...