DNA Evidence Basics: Types of Samples Suitable for DNA Testing
On this page find basic information on the following types of samples suitable for DNA testing:
Questioned or unknown samples collected from the crime scene can be any biological sample including: liquid blood or bloodstains,
liquid saliva or saliva stains, and liquid semen or dried semen stains (including from vasectomized males) deposited on virtually
any surface; genital/vaginal/cervical samples collected on swabs or gauze, or as aspirates; rectal/anal swabs; penile swabs;
pieces of tissue/skin; fingernails; plucked and shed hairs (e.g., head, pubic, body); skin cells on drinking vessels, clothing
(e.g., neck collars, waistbands, hat linings); slides containing tissue, semen, etc.; and liquid urine.
Samples collected from unidentified bodies can include: blood, buccal swabs, hairs, bone, teeth, fingernails, tissues from
internal organs (including brain), muscle, and skin.
The most common reference samples collected from known individuals are blood, oral/buccal swabs, and/or plucked hairs (e.g.,
Other samples that may be considered when individuals are unavailable or are reluctant to provide samples include clothing
where biological fluids may be deposited (e.g., women's panty crotches or blood-, saliva-, or semen-stained items) and other
clothing in close contact with the body where skin cells may have rubbed off (e.g., collars, waistbands, hats), bedding (with
vaginal/semen stains or rubbed off skin cells), fingernail clippings, cigarette butts, toothbrushes, hairs in razors and hairbrushes,
discarded facial tissues or handkerchiefs with nasal secretions, condoms, gum, feminine products, pathology paraffin blocks
or slides from previous surgery or from autopsy, and teeth.
If an individual has received transfusions shortly before the collection of a blood sample (e.g., homicide victim), the DNA
test results may indicate the presence of DNA from two or more sources. Generally the predominant DNA types reflect the types
from the individual. However, other sources of reference samples for individuals who have received transfusions may need to
be collected. These would include: blood-stained clothing or other material (bedding, etc.) and oral, vaginal, and other swabs
in addition to the items listed above.
Because a child inherits half of its DNA from each parent, it is possible to use reference samples collected from close relatives
(e.g., biological father, mother, and/or full siblings or the individual's spouse and their children) to identify or confirm
the identity of bodies that have not been identified through other means. It is also possible to use reference samples collected
from close relatives for comparison to crime scene samples, for example, in missing body cases where a bloodstain or tissue
sample from a possible crime scene can be tested to demonstrate a biological relationship to known individuals.
Aborted fetal tissue can be analyzed for determining paternity, for example, in sexual assault and/or incest cases where conception
occurred. Paternity and/or maternity of a child can be confirmed using blood or other samples listed above from the child
and the alleged parent(s).
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Date Created: August 9, 2012