Tolkein/D&D Dwarves have x0 sex chromosomes. To a biologist, all dwarves would be considered to have female sex. If they ever had a Y chromosome in their evolutionary history, it's gone without a trace now, because they never needed it. Their X chromosome has two very short legs and two long ones, so they call it a "dice cup" or "drinking cup" with some lewd associations.

To dwarves, gender is something you pick as you go along. Mothers carry their young for less time, and they come out more fully formed (including the first wisps of a beard) than humans, and there's no puberty and no rush to pick a gender. Many dwarves are just dwarves.

Dwarves who develop a "male" gender leaning often find it very validating to travel and meet the Other Races, who take one look at them and see them how they see themselves. They find the jokes that there are no female dwarves *even funnier* than we do.