The 11-year-old son of a Staten Island school teacher shot off a portion of his finger yesterday while playing with his father’s illegal gun, police said.

The West Brighton youth was home alone with his 8-year-old brother in the basement of their single- family home when the gun went off at 2:40 p.m., according to law-enforcement sources.

Michael Bilotto, a Department of Environmental Protection construction worker, was taken into custody for possession of an unlicensed handgun, police said.

Charges were pending last night.

The injured boy was treated at Richmond University Medical Center and released.

His mother, Virginia Bilotto, is a city schoolteacher, according to city payroll records.

Both parents were at work at the time of the incident, police said.