Question: Which of the following introduce genetic variation in an organisms's gametes, ensuring that no gametes have a full set of chromosomes from either the original egg or the original sperm that made the organism? Independent assortment - in Metaphase 1, either the paternal (from sperm) or the maternal (from egg) copy of each chromosome may line up on either side of the metaphase plate, so the resulting cells going into Meiosis 2 have a combination of paternal and maternal chromosomes. Crossing over - genetic material is exchanged between the maternal and paternal copy of each homologous chromosome, so each resulting chromosome is different from the parental copies. During DNA replication of the S phase, each chromosome is copied to make two sister chromatids. The centrosomes that organize the microtubules of the meiotic spindle replicate. Need Assignment Help?