In almost all Hindu families, marriage within the same gotra is prohibited, since people with same gotra are considered to be siblings.
But the hidden reason / science behind this practice is the ‘Y Chromosome‘ which is expected to be common among all male in same gotra. So, the woman too carries similar X Chromosome and if married, their offspring may be born with birth defects.
Few families even maintain their Pravara which is a list of all seers through which their Gotra was derived.
It connects to the root Seer.