My information comes from the FAQ on the Ancestry.com's DNA site. It says "The Paternal Lineage test analyzes specific segments of the Y-chromosome which is only found in males. And because the Y-chromosome is passed largely unchanged from father to son, DNA results from a male participant today can be used to represent the paternal lineage dozens of generations into the past." The "Maternal Lineage Test" traces your ancestry on your mother's side - so, your mother, to her mother, and so on. So if tracing the Whittier line, the DNA has to come from a male in the line - that's why I couldn't do it, but my brother could.

Does this help a bit? The FAQ has lots of helpful information.