Fingerprints Biological and Developmental Basis Crime Scenes in

Fingerprints Biological and Developmental Basis Crime Scenes in the Classroom Session 7 B

Fingerprint anatomy • Skin has several layers – Epidermis – Basal layer (gives rise to epidermis) – Dermis – Subcutaneous fat

Fingerprint anatomy • Some skin is hairy, some is not (glabrous) • Glabrous skin is found on palms of hands and soles of feet • Fingerprints are patterns of epidermal ridges associated with glabrous skin

Fingerprint anatomy Epidermal ridges lie on top of fleshy swellings called volar pads that form in the dermal layer of skin

Why do we have fingerprints? • Ridges improve traction when grasping

Why do we have fingerprints? • Ridges may enhance tactile sensitivity Scheibert J, Leurent S, Prevost A, and Debregeas G. 2009. The Role of Fingerprints in the Coding of Tactile Information Probed with a Biomimetic Sensor. Science 323 (5920), 1503.

Embryological development • Begins in the second or third month of gestation • Caused by simultaneous – growth of epidermal cells – shrinkage of volar pads

Embryological development • Different layers of skin grow at different rates; the middle (basal) layer out grows the dermis and epidermis • This causes the skin to buckle towards the squishy dermal layer to form a series of parallel ridges Kucken M. 2007. Models for fingerprint formation. Forensic Science International 171: 85 -96.

Embryological development • Ridges first start to form – Near the center of the volar pad – At the edges • Near nail bed • Near joint creases • Eventually the different ridges all bump up against each other Kucken M. 2007. Models for fingerprint formation. Forensic Science International 171: 85 -96.

What accounts for the different classes of fingerprints? • The precise shape and orientation of the ridges depends on – Position relative to the nail bed and joint crease – Size and shape of volar pad – Asymmetrical volar pads produce asymmetrical ridge patterns

What accounts for individual differences? • Volar pad shape and size is largely genetically determined • Those with a particular genetic mutation have no fingerprints (adermatoglyphia) Photo by Eli Sprecher, American Journal of Human Genetics

What accounts for individual differences? • Individual differences arise from subtle differences in – How quickly basal cells grow – How quickly volar pads shrink – Growth of the finger, which necessitates adding new ridges • These are all influenced by environmental conditions, so they’re different for every individual