In Dutch, the mannelijke lijn is the male line, and the vrouwelijke lijn is the female line.
Traditionally, many Dutch publications have focused on the male line only. Over the past few decades, it has become common to focus on both male and female lines, both in terms of descendants and ancestors. Most Dutch genealogists I know are researching their kwartierstaat, their ancestors in all the lines.
People interested in the female line can join Mamamito, a Belgian research project that compares mitochondrial DNA with the trees.