It is said that the birth chart indicates pitru dosham; it occurs when the oblations are not performed properly by us or by our forefathers. The ancestors get dissatisfied when we do not perform the ordained rituals or during an unnatural death. Their dissatisfaction results in bad fruits for their family like not having a progeny or having malefic effects on children. The birth chart indicates such dosham; scriptures do indeed mention on this.
Those who have performed sharanagati and do the tharpanam, sraddham, etc. accordingly need not worry to a large extent about pitru dosham as Perumal will take care. If greater problems persist in a family, they can remedy within the stipulations of Srivaishnava tradition; our elders do not perform tharpanam at Rameshwaram for atonement, instead, we do other remedies.