Short Tandem Repeat (STR) Slippage
Definition
Replication slippage at a repetitive locus where the template and nascent strands temporarily misalign. If the nascent strand slips forward, one repeat unit is added; if it slips back, a repeat is deleted. Accumulated slippage events over generations create the allelic diversity at STR loci used in forensic profiling.
- Mechanism
- Template and nascent DNA strands temporarily misalign during replication
- Forward slippage
- Adds one repeat unit
- Backward slippage
- Deletes one repeat unit
- Forensic relevance
- Generates the allelic diversity underlying STR-based DNA profiling
Common questions
How does slippage relate to the mutation rate used in kinship and paternity calculations?+
Because slippage happens at a measurable rate per generation at each STR locus, population geneticists can estimate locus-specific mutation rates from parent-child trio data, and these rates are built into paternity and kinship likelihood calculations to account for the rare cases where a true biological parent and child differ by one repeat.
Does slippage happen equally at every STR locus used in forensic panels?+
No. Mutation rate varies by locus, and loci with longer, more uniform repeat structures generally show higher slippage rates than those with shorter or more broken-up repeat patterns, which is one reason different STR loci are assigned different weight when a single-repeat mismatch appears in kinship testing.
Related terms
- DNA Polymerase
- The enzyme that synthesises new DNA by adding deoxyribonucleoside triphosphates complementary to the template strand. In humans, polymerase delta copies the lagging...
- Frameshift Mutation
- A change in the reading frame of a coding sequence caused by an insertion or deletion of a number of nucleotides that...
- Okazaki Fragment
- A short segment of DNA (100 to 200 nucleotides in eukaryotes) synthesised on the lagging template strand in the 5-prime to 3-prime...
- Point Mutation
- A change in a single nucleotide in the DNA sequence. A transition substitutes one purine for another or one pyrimidine for another...
- Semi-Conservative Replication
- The mode of DNA copying in which each daughter double helix retains one parental strand and acquires one newly synthesised strand, confirmed...