Rashi on Numbers 27:4/רש"י על במדבר כ״ז:ד׳

1למה יגרע שם אבינו WHY SHOULD THE NAME OF OUR FATHER BE DONE AWAY — We stand in the place of male children, and if you say that females are not regarded as issue in respect to inheritance, then our mother should marry her deceased husband’s brother (cf. Deuteronomy 25:5, 6) (Bava Batra 119b).

2כי אין לו בן [WHY SHOULD OUR FATHER'S NAME BE DONE AWAY WITH] BECAUSE HE HATH NO SON — Thus it follows that if he had had a son they would have made no claim of any kind: this tells us that they were women of intelligence (Sifrei Bamidbar 133:4; cf. Bava Batra 119b).