STR Marker Database: Microsatellite Markers for Pigeon Identification

Abstract: This database entry documents short tandem repeat (STR) microsatellite markers used for DNA fingerprinting in pigeons — marker properties, polymorphism levels, combined exclusion probability, and applications in individual identification and parentage verification.

STR Marker Overview

Field	Value
Marker Type	Short tandem repeat (microsatellite)
Repeat Unit	Di-, tri-, tetra-nucleotide motifs
Genome Location	Nuclear genome, distributed across chromosomes
Inheritance	Co-dominant, Mendelian
Mutation Rate	10⁻³–10⁻⁴ per locus per generation
Diagnostic Utility	Individual identification, parentage verification

Marker Panel Design

Parameter	Recommended
Loci per panel	12–20
Allele number per locus	≥ 5 (ideally ≥ 8)
Observed heterozygosity	≥ 0.6
Null allele frequency	< 0.05
Combined exclusion probability	> 99.99%

\[\text{Combined } P_E = 1 - \prod_{i=1}^{n} (1 - P_{E,i})\]

Applications

Application	Marker Requirement	Output
Parentage verification	12–20 loci, high polymorphism	Exclusion/confirmation + LR
Individual identification	12–20 loci	Unique profile (match probability)
Population genetics	15–30 loci, population-validated	Heterozygosity, FST
Inbreeding monitoring	Genome-wide or dense panel	ROH, inbreeding coefficients

See DNA Fingerprinting in Racing Pigeons for the full methodology.

Match Probability

For an individual profile, the random match probability is:

\[P(\text{match}) = \prod_{i=1}^{n} \left( 2 p_i p_j \text{ or } p_i^2 \right)\]

Where \(p_i\), \(p_j\) are allele frequencies. With 15 loci, match probabilities typically fall below 10⁻¹⁵ — far below the world pigeon population.

Marker Validation Requirements

Validation Step	Purpose
Hardy-Weinberg equilibrium test	Population validity
Linkage disequilibrium check	Independence of loci
Null allele assessment	Avoid false exclusions
Species specificity	Confirm amplification in Columba livia
Reproducibility study	Allele calling consistency

STR Marker Biology and Mutation

Microsatellites arise from replication slippage — during DNA replication, the polymerase can slip on repetitive motifs, adding or deleting repeat units. This mechanism explains their key properties:

Property	Value	Implication
Mutation rate	10⁻³–10⁻⁴ per locus per generation	Higher than SNPs (10⁻⁸)
Mutation model	Stepwise (add/delete one repeat)	Allele size-based analysis valid
Mutation bias	Slight expansion bias in birds	Rare size shifts across generations
Allele range	Typically 80–400 bp (after primer design)	Compatible with capillary electrophoresis

The stepwise mutation model has an important practical consequence: alleles differing by one repeat unit are more closely related than alleles differing by many units. This affects genetic distance calculations and the interpretation of allele-sharing in parentage analysis — closely related individuals share alleles by descent, not just by chance.

Marker Discovery and Development Process

Developing a validated pigeon STR panel follows a structured pipeline:

Step	Description	Output
1. Library construction	Shotgun or enriched genomic library	Sequence reads with repeats
2. Repeat identification	Bioinformatics scan for microsatellite motifs	Candidate loci (hundreds)
3. Primer design	Flanking primers for each candidate	Primer pairs
4. Pilot screening	Test on small panel of individuals	Polymorphic markers
5. Population validation	Genotype larger population	Allele frequencies, HWE
6. Panel assembly	Select loci meeting criteria	Final validated panel
7. Reproducibility study	Repeat genotyping	Allele-calling consistency

Cross-species transfer of pigeon markers to other Columbidae species (doves) is often possible but requires re-validation — primer binding sites may differ.

Population Genetic Statistics in Detail

Hardy-Weinberg Equilibrium (HWE)

For a locus with alleles \(p_i\), expected heterozygosity under HWE:

\[H_e = 1 - \sum p_i^2\]

Deviation from HWE signals:

Deviation	Possible Cause	Action
Heterozygote deficit	Inbreeding, null alleles, population structure	Investigate null alleles; check sampling
Heterozygote excess	Outbreeding, recent admixture	Verify sampling design
Significant HWE departure	Locus problems	Consider excluding the locus

Polymorphism Information Content (PIC)

PIC measures a marker's informativeness:

\[PIC = 1 - \sum p_i^2 - \sum_{i<j} 2 p_i^2 p_j^2\]

PIC Value	Informativeness
> 0.7	Highly informative
0.5–0.7	Moderately informative
< 0.5	Poorly informative — consider replacement

A validated pigeon panel should consist predominantly of highly informative loci (PIC > 0.7) to maximize exclusion power per marker.

Null Alleles

Null alleles fail to amplify due to primer-binding site mutations, causing apparent homozygosity:

Null Allele Frequency	Severity	Action
< 0.05	Acceptable	Monitor
0.05–0.10	Caution	Consider redesign of primers
> 0.10	Problematic	Redesign primers or drop locus

Null alleles in parentage analysis create false exclusions — a parent that appears to share no allele with a chick may actually carry a null allele. Software (e.g., CERVUS, ML-Relate) estimates null allele frequencies and accounts for them.

Worked Example: Computing Combined Exclusion Probability

Consider a panel of 15 loci with single-parent exclusion probabilities as follows (typical values for pigeon microsatellites):

Locus	Alleles	PE (single parent)
1	9	0.58
2	10	0.61
3	8	0.55
4	11	0.63
5	7	0.52
6	9	0.58
7	12	0.65
8	8	0.55
9	10	0.61
10	9	0.58
11	6	0.47
12	8	0.55
13	10	0.61
14	7	0.52
15	9	0.58

Combined single-parent exclusion probability:

\[P_E = 1 - \prod (1 - P_{E,i}) \approx 1 - (0.42 \times 0.39 \times ...) \approx 0.99996\]

With both parents tested, the combined exclusion probability exceeds 0.999999 — effectively certain exclusion of falsely assigned parents.

Genotyping Workflow and Quality

Step	Method	Quality Check
DNA extraction	Spin-column	Yield, purity
Multiplex PCR	5–6 loci per dye channel	Positive/negative controls
Fragment analysis	Capillary electrophoresis	Size standard in every injection
Allele calling	Software (e.g., GeneMapper, Geneious)	Bin editing, stutter filtering
Data export	LIMS integration	Sample-locus cross-check

Stutter Peaks and Their Management

PCR of STR loci produces stutter artifacts — peaks one repeat unit shorter than the true allele (from slippage during early PCR cycles). Stutter complicates calling:

Stutter Ratio	Handling
< 15% of main peak	Ignore (typical)
15–30%	Caution; use validated bins
> 30%	Consider alternate locus or redesign

Software-based genotyping with validated bin sets manages stutter reliably; manual calling should be double-reviewed.

Database Applications in Practice

Parentage Verification Cases

Case Type	Panel Requirement	Typical Outcome
Sire exclusion	12–20 loci	Exclusion at ≥ 2 loci → excluded
Full parentage (sire + dam)	15–20 loci	Combined PE > 99.99%
Half-sib verification	20+ loci	Higher power needed for sibship
Identity match	15+ loci	Random match < 10⁻¹²

Individual Identification Statistics

The random match probability for a 15-locus profile (all heterozygous, allele frequencies ~0.1):

\[P(\text{match}) = \prod 2 p_i p_j = (2 \times 0.1 \times 0.1)^{15} \approx 2 \times 10^{-15}\]

Far below the global pigeon population (~5 × 10⁸) — profiles are effectively unique.

Inbreeding Monitoring

Metric	Calculation	Use
FIS (within-population inbreeding)	1 - Ho/He	Loft-level inbreeding
Pairwise relatedness	Queller-Goodnight or Lynch-Ritland	Mate selection
ROH (with SNP data)	Genomic runs of homozygosity	Genome-wide inbreeding

Pairwise relatedness values guide mate selection: avoiding matings with relatedness > 0.125 (first cousins or closer) preserves diversity.

References

1. Jamieson, A.; Taylor, S. S. Comparisons of three probability formulae for parentage exclusion. Animal Genetics 1997;28(6):397-400. DOI: 10.1111/j.1365-2052.1997.00186.x
2. Presti, F. T.; Wasko, A. P. A review of microsatellite markers and their applications in birds. Genetics and Molecular Research 2014;13(1):2152-2164. DOI: 10.4238/2014.March.31.2
3. Trachtulec, Z.; Vyleťal, P. et al. Genetic variation of the domestic pigeon (Columba livia). Folia Zoologica 2010;59(1):11-17

---

Return to Research Database Overview or read CHD Gene Database.