I am very confused about crossing over. It is said that crossing over increases genetic variation as it is a combination of paternal and maternal chromosomes. However, crossing over occurs in meiosis 1 but meiosis 1 occurs before fertilisation, so my question is how are there paternal chromosomes in an egg cell prior to fertilisation.
when they say paternal chromosome, they mean chromosome of the father of the organism. Not the father of the offspring of the specific organism. During meiosis ,in order to form the gametes, the chromosomes of the mother and the father of a specific organism interact, because homologous chromosome pairs consists of a pair of the organism's fathers chromosomes, and the mother's. please tell if you still don't get it.