Twin Zygosity: DNA-Based Testing

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Condition Description


Twins can be either monozygotic (identical) or dizygotic (non-identical). Identifying zygosity of twins is essential in diagnosing and treatment of certain genetic conditions. Testing may be performed on prenatal and postnatal samples. Samples from the twins, as well as both maternal and paternal blood, must be submitted. Amniocytes, chorionic villus, or blood samples from the twins can be used for analysis.


Comparative analysis of DNA samples has been conducted using PCR of polymorphic sites at the following fifteen markers: D8S1179, D21S11, D7S820, CSF1PO, D3S1358, TH01, D13S317, D16S539, D2S1338, D19S433, vWA, TPOX, D18S51, D5S818, FGA. Fragment analysis was performed using capillary electrophoresis.

Parental samples are used to determine likelihood of dizygotic twins having the same allelic pattern as monozygotic twins.

Detection and Reference Range

Over 99% of twin pairs tested will be determined to be monozygotic or dizygotic.
Reference Range
Qualitative assay.

Specimen Requirements

When sample fails to meet the acceptable criteria, please call 470.378.2200 and ask to speak with a laboratory genetic counselor (

Type: Whole Blood

Specimen Requirements:

In EDTA (purple top) tube:
Infants (<2 years): 2-3 ml
Children (>2 years): 3-5 ml
Older Children & Adults: 5-10 ml

Specimen Collection and Shipping: Refrigerate until time of shipment. Ship sample within 5 days of collection at room temperature with overnight delivery.

How to Order

Requisition Forms