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lecture_notes_10_15_07 - Mitosis and Meiosis outline...

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Mitosis and Meiosis outline – Lecture 3 2007 Mitosis and Meiosis [Reading: SS 18-31; CR 218-228, 243-249] Mitosis in eukaryotes As a means of reproduction, mitosis is: A mechanism of cellular reproduction to form identical cells A process to condense (shorten) chromosomes and deliver identical copies from a parent cell to two daughter cells Karyokinesis divides the nucleus into two equivalent nuclei Cytokinesis follows, to divide the cytoplasm and separate the divided nuclei and cytoplasm into daughter cells Basic chromosome terminology Nuclear membrane (or envelope) surrounds the chromosomes in interphase A centromere or kinetochore (spindle fiber attachment region of a chromosome) which separates the chromosome into 2 arms (sometimes 1) Chromosomes come in pairs of homologues (equivalent chromosomes from each parent), one from each parent Each homologue forms an identical sister chromatid (copy of a chromosome) during replication (duplication of DNA or chromosomes) Chromatids sometimes are referred to as strands in meiosis n: basic haploid chromosome number, number of chromosomes in a gamete e.g. n = 23 for humans 2n: basic diploid chromosome number, number of chromosomes in a zygote e.g. 2n = 46 for humans n varies as a function of life cycle Chromosome shortening = coiling = condensation ; elongation = uncoiling = decondensation Moving chromosomes – the spindle
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