During which phase of the cell cycle is a cell's dna copied?

The answer to this question will be "Mitosis." During Mitosis the DNA cell is replicated during the cell cell cycle. Mitosis is basically cell division that equals two copied daughter cells with the same amount of chromosomes as each other during the cell cycle.

Hope this helps.

not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.