10.1 Meiosis

Essential idea:  
Meiosis leads to independent assortment of chromosomes and unique composition of alleles in daughter cells.
Understandings: Nature of science:
    Chromosomes replicate in interphase before meiosis.

    Crossing over is the exchange of DNA material between non-sister homologous chromatids.

    Crossing over produces new combinations of alleles on the chromosomes of the haploid cells.

    Chiasmata formation between non-sister chromatids can result in an exchange of alleles.

    Homologous chromosomes separate in meiosis I.
    Sister chromatids separate in meiosis II.

    Independent assortment of genes is due to the random orientation of pairs of homologous chromosomes in meiosis I.

    Making careful observations—careful observation and record keeping turned up anomalous data that Mendel’s law of independent assortment could not account for. Thomas Hunt Morgan developed the notion of linked genes to account for the anomalies. (1.8)
Applications : Guidance:
      Diagrams of chiasmata should show sister chromatids still closely aligned, except at the point where crossing over occurred and a chiasma was formed.

    Skill: Syllabus and cross-curricular links:
      Drawing diagrams to show chiasmata formed by crossing over.

    Biology
    Topic 1.6 Cell division
    Topic 3.3 Meiosis
    Topic 11.4 Sexual reproduction

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    HL Topic 10 Genetics Copyright © by Alex Black. All Rights Reserved.

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