Final answer:
Most hair specimens lack the root where nuclear DNA is concentrated, leading to a scarcity of usable genetic material for forensic identification purposes, and they are prone to contamination.
Step-by-step explanation:
Most hair specimens found at crime scenes are not ideal sources for DNA analysis because often, the hair is naturally shed and lacks the root. The root of the hair is where the majority of the DNA is found, specifically nuclear DNA, which is used for forensic testing and genetic profiling. Without the root, the hair typically only provides mitochondrial DNA, which is less useful for identifying individuals uniquely unless maternal lineage is in question. Furthermore, hair can also be easily contaminated with DNA from other sources, making it a less reliable source of DNA evidence for criminal investigations.