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Meiosis, comparison of mitosis and meiosis, genetic variation, independent assortment, crossing over, random fertilization

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Life Science
LIFE 102
Louis Bjostad

25 MarchConcept 133 Meiosis reduces the number of chromosome sets from diploid to haploidLike mitosis meiosis is preceded by the replication of chromosomesMeiosis takes place in two sets of cell divisions called meiosis I and meiosis IIThe two cell divisions result in four daughter cells rather than the two daughter cells in mitosisEach daughter cell has only half as many chromosomes as the parent cellThe Stages of MeiosisIn the first cell division meiosis I homologous chromosomes separateMeiosis I results in two haploid daughter cells with replicated chromosomes it is called the reductional divisionIn the second cell division meiosis II sister chromatids separateMeiosis II results in four haploid daughter cells with unreplicated chromosomes it is called the equational divisionMeiosis I is preceded by interphase in which chromosomes are replicated to form sister chromatidsThe sister chromatids are genetically identical and joined at the centromereThe single centrosome replicates forming two centrosomesProphase IProphase I typically occupies more than 90 of the time required for meiosisChromosomes begin to condenseIn synapsis homologous chromosomes loosely pair up aligned gene by geneIn crossing over nonsister chromatids exchanged DNA segmentsEach pair of chromosomes forms a tetrad a group of four chromatidsEach tetrad usually has one or more chiasmata Xshaped regions where crossing over occurredMetaphase I
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