BELLEFONTE, Pa. — A son of the former Penn State University assistant football coach Jerry Sandusky pleaded guilty Friday to charges that he pressured a teenage girl to send him naked photos and asked her teenage sister to give him oral sex.

The plea deal for Jeffrey Sandusky, Jerry Sandusky’s son, comes one week before his trial was to begin, and nearly six years after his father was arrested in a child molestation case that shook Penn State and is still working its way through criminal and civil courts.

Jeffrey Sandusky pleaded guilty to all 14 counts, including solicitation of statutory sexual assault and solicitation of involuntary deviate sexual intercourse.

A call seeking comment from his lawyer was not immediately returned Friday.

As part of the deal, Mr. Sandusky, 41, will spend up to six years in state prison, but the judge could impose a sentence of as much as eight years.