Leukocyte
Definition
White blood cell. The forensically critical component of blood because it contains a nucleus with a full complement of genomic DNA. Leukocytes are present in whole blood at concentrations of 4,000 to 11,000 per microlitre, providing ample DNA template even in small stains.
- Common name
- White blood cell
- Forensic relevance
- Contains nucleated genomic DNA
- Concentration in whole blood
- 4,000 to 11,000 per microlitre
- Contrast
- Red blood cells lack a nucleus and DNA
Common questions
Why can DNA be recovered from a blood stain if red cells lack nuclei?+
Red blood cells make up most of blood's volume but are anucleate, so all the nuclear DNA available for STR typing or other genetic analysis comes specifically from the leukocyte fraction, even though leukocytes are a minority of the cells present.
Does a small blood stain still yield enough DNA for typing?+
Usually yes, because even a small stain contains thousands of leukocytes per microlitre of original blood, giving ample nucleated template for standard STR profiling unless the stain is also heavily degraded by environmental exposure.
Related terms
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- Degradation
- The breakdown of DNA by enzymatic, chemical, or physical processes after biological material is deposited. Degradation produces fragmented DNA that may not...
- Mitochondrial DNA (mtDNA)
- DNA located in mitochondria rather than the cell nucleus. Present in hundreds to thousands of copies per cell, making it recoverable from...
- Presumptive Test
- A fast, low-cost, class-specific screen used to triage a caseload before instrumental work begins. Examples are Marquis reagent for opioids and amphetamines,...
- Short Tandem Repeat (STR)
- Short repetitive DNA sequences scattered throughout the genome, with the number of repeats varying between individuals at each locus. DNA profiling compares...