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Mitosis Forming Diploid Cells All Cells Except Gamete Cells (in ovaries and testes) Interphase • 46 chromosomes in humans • Chromatin • Replicates DNA – Sister chromatids – Centromere • Prepares for nuclear division Prophase • Centrioles split and move to opposite ends – Attachment for spindle fibres (“guide wires”) – No centrioles in plant cells • Chromosomes condense • Centromeres attach to spindle fibres • Nuclear membrane dissolves – Separation of chromosomes and cell organelles Metaphase • Chromosomes line up at equatorial plate • Nuclear membrane completely dissolved Anaphase • Centromeres divide • Sister chromatids become singular chromosomes • Chromosomes move to opposite poles • Identical set of chromosomes at each pole Telophase • Chromosomes lengthen • Spindle fibres dissolve • Nuclear membrane forms – 46 chromosomes Cytokinesis • Cytoplasm divides • Furrow develops • Pinch off cell into two parts • Plant cells – cell plate forms between chromatin masses – Cell plate becomes new cell wall Meiosis Forming Haploid Cells Gametes Specific to Meiosis • Two stages of cell division • Chromosome number in daughter cells is half the number in the parent cells • Haploid = n Diploid = 2n n=23 2n=46 Meiosis I • DNA Replication takes place before • Prophase I: – – – – – Nuclear membrane dissolves Centrioles split Chromosomes come together as homologous pairs Spindle fibres form Synapse and crossing over *Tetrad (four chromatids) • Metaphase I: – Homologous chromosomes attach to spindle fibres – Line up along equatorial plate • Anaphase I: – Each chromosome separates from homologue – Move to opposite poles (segregation) • Telophase I: – Nuclear membrane forms – Not identical chromosomes (sister chromatids) – Cytokinesis Meiosis II • DNA does NOT replicate • Prophase II: – Nuclear membrane dissolves – Spindle fibres form – Centrioles move to opposite poles • Metaphase II: – Chromosomes line up along equatorial plate – Attached at centromere (and to spindle fibres) • Anaphase II: – Chromatids break apart – Move to opposite poles – Nuclear membrane forms • Telophase II: – Cytokinesis (cytoplasm seperates) – Four haploid daughter cells • Chromosome number has been reduced to half • These cells may become gametes