Is it or how is it possible to know what race/ethnicity or origin a person is or comes from just from their hair?
I need to know if it is possible to tell what ethnic origin a person is by looking at their hair under a microscope or is there some sort of DNA analysis that can tell us this? I know that it can be difficult because of the "racial" mixtures of a person. Please let me know. Thank you.
When viewed under the microscope in cross-section, human hair indeed has characteristics indicative of race or ethnicity. The most basic distinction is the cross-sectional shape of the hair shaft as follows:
Caucasoid (white) hair = oval cross-section
Negroid (black) hair = flat cross-section
Mongoloid (Asian) hair = round cross-section
There are also racial differences in pigmentation, thickness of the hair cuticle, and prevalence of surface undulations.
Additional and more specific racial/ethnic information is available using DNA. This is especially true if the hair bulb is present. DNA studies can reveal genetic markers characteristic of ethnic groups around the world.
Finally, if hair bulbs and DNA are recovered, it is possible to identify the individual, so long as a DNA sample from the suspect individual is available for comparison.
In short, the answer to both of your questions is maybe.
Hair analysis under a microscope is not a foolproof way to identify race, but establishing hair type (commonly used are observations/measurements of the cuticle, tip, width, medulla, and color) can give a strong indication of race and certainly rule out some races.
DNA analysis derived from hair samples (or any other source of DNA) can give a stronger indication of race, as there are certain genetic markers that are present in the populations of certiain areas. The presence or lack of markers in a sample can be used to piece together an individual's ethnic/geographic origins. As you mention, someone with ancestors from different parts of the globe might have a more confusing picture, but that is not to say that their ancestry could not be determined. There are actually companies that will perform this service for you. Links to two major ones are below, as well as an FBI guide to hair analysis.