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Paediatric Laboratory Medicine

Identity Testing: Zygosity Studies

Clinical Significance

Individuals can be distinguished from one another by DNA fingerprinting, which compares nine to sixteen variable DNA markers in different regions of the genome. Each person has their own pattern of markers - a DNA ‘fingerprint’. PCR amplification followed by gel electrophoresis allows comparison of these markers from different individuals. This method can be used to determine the biological relationships between family members such as identity and zygosity testing. Determining the relationships between family members can be very important if a genetic cause for a disease is being considered, since the genetic diagnosis of one family member may apply to the other family members as well. DNA fingerprinting can also be used to evaluate the purity of tissue samples obtained for other kinds of tests. Maternal cell contamination of fetal cell samples obtained for prenatal analysis can be assessed in this way, and sample mix-ups or labeling errors can be detected by using DNA fingerprinting to match tissue samples from the same person taken at different times. DNA fingerprinting is also used to distinguish between the X and Y chromosomes for sex determination.

Test Name

Identity Testing: Zygosity Studies

Test Code



Molecular Genetics


STR (short tandem repeat) analysis

External Proficiency Testing


Turn Around Time

2 weeks (Prenatal samples), 2-3 weeks (Pregnancy/Urgent samples), 4-6 weeks (Routine)


Zygosity Testing

Specimen Type

Blood; gDNA. 

For details about specimen requirements, please refer to: Specimen Type & Requirements (PDF).

Minimum Specimen Requirements

5-10 mL EDTA or ACD 0.5 mL EDTA (neonate); minimum 10 ug in 100 uL low TE (pH8.0)


Room Temperature

Special Requirements

Special Instructions for Genome Diagnostics Samples

If sample shipment >48 hours, ship on ice.

Approval is not required

CPT Codes


Shipping and Contact Information

The Hospital for Sick Children
Rapid Response Laboratory
170 Elizabeth Street, Room 3642
Toronto, ON
M5G 2G3
Phone: 416-813-7200
Phone: 1-855-381-3212


Interpretation is provided in report