During the S (DNA synthesis) phase at interphase in meiosis I, DNA replication occurs here where the chromosomes are doubled. This phase does not occur in meiosis II. At the end of meiosis II, the chromosome number becomes halved in the sex cells. The cell just goes on to divide to ensure haploidy of chromosomes in the gametes such that the sperm from the male and egg from female are both haploid. Fertilization brings about diploidy of the zygote itself
This is also called light. They can move through empty spaces because do not need a medium and they are the fastest because no matter how far they are they do not get smaller.
