![]() This is why children look a bit like their parents, but not exactly. Crossing over also shuffles the deck of DNA, making new combinations of the differences between the chromosomes that we inherited from our parents. Without crossovers, the wrong number of chromosomes may end up in the sperm or egg cells. The connections provided by crossovers are important for the accurate distribution of chromosomes. In preparation for the first division, chromosomes closely associate into matching pairs and then become connected by crossing-over – the breakage and rejoining of chromosome arms. The process is controlled by proteins including SUMO and ubiquitin. Early on (prophase I) chromosomes form a few crossovers to exchange DNA. To achieve these goals, the meiotic cells go through two rounds of division and a number of preceding stages that you can find in any good biology text book, like these: ![]()
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