In Kiddushin on daf 75a, the mishna says that you have to check the mothers of the wife but not the fathers of the wife. later on in the gemara it asks why doesn't the wife examine the groom's lineage.
If by males there's a "voice" proving the pure lineage, what would be the purpose of the wife checking groom's lineage. Doesn't the groom already have a "shem tov".
Ariel Kirsch
It is clear from the Mishnah itself that the rule that a man's lineage need not be checked is not ironclad. The Mishnah teaches that we do require one to check the woman's father's mother and her mother's father's mother, although any Pesul found there would have had to be carried by a male.
From this we may conclude that although, in general, we do not suspect a Pesul in males, nevertheless we check for undiscovered Pesulim in their maternal lineage. In the same manner, we would have required checking groom's lineage (if Kesheiros were not allowed to marry Pesulim), as the Gemara you quoted asks.
D. Zupnik
Dear Ariel
I would approach it like this. If a male has a Pesul, word will get out. If a female has a Pesul, it remains hidden. Therefore, when one comes to marry he must inquire about the status of the females not the males. He therefore doesn't check the status of his father in law, but he still has to check the status of the father in law's mother because if she had a Pesul that would remain covered. But if the father in law's father had a Pesul we'd all know about it and therefore there is no need to check. In other words, the fact that when males fight the issue of Yuchasin surfaces, tells me that if the person, or his father (or grandfather etc) had a Pesul from the male side of his lineage people would know about it. However it is possible that this person's mother was problematic, without us knowing about it. That's why the Mishnah requires checking out the bride's mother, not father, but checking out the father's mother.
Now when the Gemara asks that we should have her check out the groom's lineage, it means that she mustcheck out his mother, his father's mother etc. -- i.e. not him personaly but his mother's side of his lineage.
I hope this clears it up. If not please don't hesitate to ask again. In the meantime keep on Shteiging and have a Kesivah va'Chasimah Tovah.
Yehuda Landy