During the process of mitosis, which event occurs to each chromosome in the cell nucleus? O Each chromosome breaks apart into individual pieces, called genes
O Each chromosome merges with another chromosome forming a tetrad
O Each chromosome is pulled apart, forming identical chromatids
O Each chromosome is pulled apart, forming two nonidentical chromatids

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genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).

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water, ice, acids, salts, plants, animals, and changes in temperature are all agents of weathering. weathering is the breaking down or dissolving of rocks and minerals on earths surface. once a rock has been broken down, a process called erosion transports the bits of rock and minerals away.