Meiosis

Nature of science:

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)

• 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.

Applications and skills:

• Skill: Drawing diagrams to show chiasmata formed by crossing over.

Guidance:

• Diagrams of chiasmata should show sister chromatids still closely aligned, except at the point where crossing over occurred and a chiasma was formed.

• Syllabus and cross-curricular links:
• Biology
• Topic 1.6 Cell
• division Topic 3.3
• Meiosis
• Topic 11.4 Sexual reproduction

Aims:

• Aim 6: Staining of lily anthers or other tissue containing germ-line cells and microscope examination to observe cells in meiosis are possible activities.