1. Cell division

    1. Cell cycle

    2. Events in Mitosis

      1. Prophase

      2. Metaphase

      3. Anaphase

      4. Telophase

      5. Cytokinesis

  2. Meiosis

    1. Importance

      1. Provides a mechanism of mixing so as to obtain one haploid genome from each parent.

      2. Production of gametes and their specialization

    2. Events

      1. Prophase I

        1. Leptotene (condensation)

        2. Zygotene (pairing) synapsis; the formation of the synaptomenal complex

        3. Pachytene (recombination), rDNA amplification, histone synthesis, LONG

        4. Diplotene (synthesis) - chiasmata (attachments) form, mRNA rRNA, LONG

        5. Diakinesis (recondensation)

      2. Reductional division .

      3. Equational division.

      4. Nondisjunction.

  3. Mutations affecting these processes

  4. Sex linkage

    1. Some genes segregate according to the sex of the organism

    2. The pattern of sex determination depends on the organism

      1. Flies and people XX vs XY

      2. Worms XX vs XO

      3. Moths and birds ZW vs ZZ

    3. The difference can be through homogametic and heterogametic individuals or through dosage.

  5. Bridges used nondisjunction to draw the most convincing link between genes and the chromosomes

    1. Obtained rare red eyed sterile males (w+) or white-eyed females (wwY)

    2. Confirmation of genotype by histology

    3. Further testing of exceptional females which were mated to w+Y males

    4. Conclusions

      1. Chromosomes are the repository of genetic information

      2. At least one X chromosome is essential

      3. In Drosophila the Y chromosome is essential only for male fertility

      4. In Drosophila being tripleX is lethal.

  6. Consequences of having sex chromosomes signal sexual differentiation.

    1. Genetically they lead to a different type of expression (criss-cross)

    2. Developmentally the chromosomes need not be the repository of sex determining genes (although they may: compare the human Y to the Drosophila Y). Rather the chromosomes serve as a signal.

    3. Because the chromosomes are the signal, individuals of one sex and only one copy of a gene while the other has two.

    4. Therefore, a mechanism must exist to compensate for this dosage difference. In fact several mechanisms exist

  7. Nondisjunction can occur with non-sex chromosomes. These produce aneuploid individuals

    1. Types of changes

      1. Nullisomic

      2. Monosomic

      3. Trisomic