Re: When does organelle replication happen in Mitosis/Meiosis?

The mitochondria and chloroplasts (if present) are maintained throughout the cell cycle, and replicate independently of the mitosis or meiosis of the cell. Mitochondrial and chloroplast replication also occurs throughout much of the cycle, with some variation between species. During mitosis the mitochondria and chloroplasts present in each dividing cell are distributed between the two daughter cells. Following cell division the number of mitochondria and chloroplasts per cell typically increases by further division of the organelles, accompanied by replication of the respective organellar genomes. Organellar replication is thus distinct from the replication of the nuclear genome (which occurs only during S phase of the cell cycle). In the case of chloroplasts, the intensity of the ambient light as well as the day/night cycle also affect the degree and timing of chloroplast division. For a review of chloroplast replication, see the review by J. V. Possingham in the 1980 Annual Review of Plant Physiology.