<span>He meant the micro-organisms (microbes) are very small living organisms but plays an important role in maintaining life on earth. Microbes fix gases and break down animal matter and dead plants into simpler substances that are used at the beginning of the food chain. Pasteur shows that vaccines against infectious diseases can be manufactured. </span>
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The longitudinal halves of a chromosome that has undergone replication are known as chromatids. They will not be called chromosomes until after they are separated during Mitosis. Mitosis distribute the chromatids to daughter cells as a cell divides. The chromosomes are initially replicated in cells undergoing Meiosis, as in preparation for the mitotic division, but then, these chromosomes are divided twice so that four daughter nuclei are produced, each having the haploid chromosome number.
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Crossing over occurs at the four-strand stage when two homologous chromosomes, each consisting of a pair of sister chromatids, are paired. Each crossover involves just two of the four strands and generates two recombinant strands.
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