Before mitosis and meiosis I, DNA is duplicated.
Explanation:
Cells go through a cell cycle from the time they are created until they die. This cycle has different stages or phases, known as G1, S, G2 and M. During G1, the cell prepares to divide, producing the proteins needed. After that, it enters the S phase, which is when the cell duplicates all its DNA. Then follows the G2 phase, it also prepares for cell division. Then follows the M phase, which is the division of the cell nucleus where the two copies of its genetic material that were created during the S phase are distributed, thus forming two genetically identical daughter cells in mitosis, which is the type of cell division that takes place on somatic cells.
Prophase is the first stage of mitosis, so when the cell enters this stage, it will have twice as much genetic material (which doubles during the S phase of the cell cycle). Also, an achromatic spindle is formed, the nuclear membrane disappears and the chromosomes condense. The next stage is metaphase, where the duplicated chromosomes line up in the center of the cell. Then during anaphase, the microtubules of the cell separate the chromosomes in opposite directions, towards the poles of the cell. Finally, during telophase, the nuclear membrane is re-formed and chromosomes are already in each newly formed daughter cell. So, now each daughter cell will have its own copy of genetic material, since it was duplicated during the S-phase.
For the formation of gametes, a similar process called meiosis occurs, consisting of meiosis I (chromosomes are separated) and meiosis II (sister chromatids of the same chromosome are separated). During the S phase, before meiosis I occurs, DNA is also duplicated. The process of meiosis is similar: prophase, metaphase, anaphase, telophase (the only difference is that during prophase, an exchange of genetic material occurs between the two homologous chromosomes). Then, at the end of meiosis I, two daughter cells are formed, each of which received half of the genetic material that was duplicated in the parent cell. This is the same amount of DNA that the daughter cells get during mitosis. During meiosis II, the sister chromatids are separated, forming two more daughter cells but they will have half of the genetic material, since there is no DNA duplication between meiosis I and II. So, this division is different. However, before mitosis and meiosis I, DNA duplication takes place.
