The verse is simple, but the timing is everything. Targum Pseudo-Jonathan on Genesis 41:50 reports that Joseph fathered two sons "before the year of famine arose," born to Asenath, raised in the house of Potiphera prince of Tanis.
Why the Torah dates the births so precisely
The rabbinic tradition reads the timing as a legal and moral statement. The Talmud (Taanit 11a), the central compilation of Jewish law and lore redacted around 500 CE in Babylonia, cites a principle: one should not bring children into the world during a time of famine. Joseph fulfills this exactly. Both boys — Manasseh and Ephraim — are born in the seven years of plenty, before the land turned lean. The Aramaic paraphrase, whose final redaction belongs to the Land of Israel around the seventh or eighth century CE, preserves the chronology for readers who would catch its weight.
Two sons who become two tribes
Manasseh and Ephraim will be elevated by Jacob himself to the status of their uncles (Genesis 48:5), becoming the tribes that carry Joseph's name forward into the land. Their births in Egypt during the plenty years are the seed of that future — the generation that will leave Egypt centuries later will trace back to these two boys, born to an Egyptian-raised mother and a Hebrew father, between harvest and famine.
The takeaway
The Torah dates births the way it dates covenants. Joseph's children came in the season of abundance, the right time to welcome a life.