When gene duplication occurs to its ultimate extent by doubling all genes in a genome

The gene duplication occurs to its ultimate extent by doubling all genes in a genome during mitosis.

Explanation:

Mitosis is a process by which an Eukaryotic organism divides its cells into two cell keeping all the genetic setup and the genetic configurations same. During mitosis, at first, during the G0 phase of mitosis, the cell prepares itself for mitosis, where it duplicates its DNA and some of the other proteins required during cell division.

During the mitosis these DNAs concentrate as different chromosomes and are separated and pulled apart into two different poles by spindle fibers and two new cells are eventually formed. Thus, during mitosis, cells produce ultimate gene duplication.