This verse is a pivotal line in the story of Joseph in Genesis. It's spoken by Joseph's brothers to Joseph himself (though they don't recognize him) when they've traveled to Egypt to buy grain during a famine. Let's break down the meaning:

"We are twelve brothers, sons of our father...": This establishes their family connection and the fact that they are numerous. It highlights that they are a substantial family unit.

"...one is no more...": This is a reference to Joseph himself. The brothers sold him into slavery years ago, and to cover their tracks, they led their father, Jacob, to believe that Joseph was killed by a wild animal. So, from their perspective (and from Jacob's), Joseph is dead.

"...and the youngest is today with our father in the land of Canaan.": This refers to Benjamin, Jacob's youngest and favored son after Joseph's supposed death. Because Jacob is old and has already suffered the loss of one son, the brothers are reluctant to bring Benjamin with them to Egypt, fearing they might lose him too. This creates a central conflict in the narrative.

In essence, the verse is significant for several reasons:

It establishes the pretense of the brothers. They are trying to appear as honest and forthright men seeking grain.
It reveals their past deception. Their statement about the missing brother is a lie they've maintained for years.
It sets the stage for further conflict. Joseph's reaction to this information, especially concerning Benjamin, drives the rest of the narrative. He uses this information to test their character and see if they have changed since they sold him into slavery.
It highlights Jacob's continued grief and favoritism. The mention of Benjamin emphasizes Jacob's love for his youngest son and his reluctance to let him go, setting the stage for Joseph's test.

In short, this seemingly simple verse is packed with information that is vital to understanding the complex relationships and dramatic events that unfold in the story of Joseph and his brothers.