Large mixing, family structure, and dominant block in the neutrino mass matrix

A possible connection between the flavour structure of the charged fermions and the large $\nu_\mu-\nu_\tau$ mixing motivates an ansatz for the neutrino mass matrix with a dominant block. We distinguish between a general form and the specific forms of the ansatz, and concentrate on the cases of phenomenological interest. The general form can incorporate an observable amount of CP violation in the leptonic sector. Only specific forms can incorporate the Mikheyev-Smirnov-Wolfenstein solutions for solar neutrinos, with small or large mixing angles. Other specific variants explain the Los Alamos neutrino anomaly, or provide a two-neutrino hot dark matter component.