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Meiosis Lecture Summary.doc

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Western University
Biology 1201A
Richard Gardiner

Meiosis Lecture SummarySexual vs Asexual ReproductionAsexual individual inherits all genes from one parent identical to parent genetic variation comes from mutations reduced ability to evolveSexual getsgenetic variation from one parent different from parents variationLife Cycles a diagrammatic representation of the events in an organismSexual Cycle in Humans somatic cells23 pairs of chromosomes chromosomes have many genes each gene occupies a specific lociaddress on a specific chromosomeshomologous chromosomes have homologous genes at homologous locibut the 2 genes need not to be identical alternate forms of the same genes they are same size same order same loci but different allelesSex Chromosomes different homologous chromosome female XXmale XYAutosomes all other nonsex chromosomesPhases of Meiosis Meiosis 1 reduces ploidy level from 2n too n Meiosis 2 divdes the remaining set of chromosomes in a mitosis like processMeiosis 1 has four phases P M A T during the preceding interphase the chromosomes are replicated to form sister chromatids Prophase I Chromosomes condense and homologous chromosomes pair up to form tetrads in a process called synapsis special proteins attach homologous chromosomes tightly togetherchromatids of homologous chromosomes are crossed chiasmataspindle forms from each centrosomes and spindle fibres attached to Kinetochore on the chromosomes begin to move the tetrads aroundMetaphase I tetrads arranged at metaphase plate microtubules from one pole attach to kine
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