Some human traits and diseases are completely heritable, some partially

1. Some human traits and diseases are completely heritable, some partially heritable, and some are not influenced by genes at all Results of class survey

2. Results of class survey

3. II. Mitosis and Meiosis

4. II. Mitosis and Meiosis Human karyotype (a photograph of the matched chromosomes) 22 pairs of homologous chromosomes (one paternal, one maternal) 1 pair of sex chromosomes

5. II. Mitosis and Meiosis A cell cycle

6. II. Mitosis

7. II. Mitosis Replication of the DNA of each chromosome. In the form of chromatin, DNA is NOT condensed. It is long and stringy.

8. II. Mitosis Figure depicts two chromosomes (long and short), and male (blue) and female (orange) homologous copies of those chromosomes sister chromatids Note that the chromosomes have been duplicated. The two members of the duplicated pair are known as sister chromatids. Centrioles migrate to opposite poles of the cell. Centrioles may be responsible for organizing microtubules into spindle fibers.

9. II. Mitosis Figure depicts two chromosomes (long and short), and male (blue) and female (orange) homologous copies of those chromosomes Period of movement of sister chromatids to the equatorial plane of the cell. Movement occurs by binding of microtubules to the kinetochore, a centromeric structure composed of layered proteins.

10. II. Mitosis Figure depicts two chromosomes (long and short), and male (blue) and female (orange) homologous copies of those chromosomes Note that homologous pairs of chromosomes do not pair up This is important because they do pair up in Meiosis I

11. II. Mitosis Figure depicts two chromosomes (long and short), and male (blue) and female (orange) homologous copies of those chromosomes The sister chromatids of each chromosome disjoin. For complete disjunction to occur, each centromeric region must be split in two, signaling the initiation of anaphase. Once anaphase occurs, each sister chromatid is referred to as a daughter chromosome.

12. II. Mitosis and Meiosis Basic chromosome anatomy

13. II. Mitosis cytokinesis - division or partitioning of the cytoplasm

14. II. Mitosis

16. II. Mitosis and Meiosis

17. II. Mitosis and Meiosis homology search begins synapsis, crossing over chiasmata visible Unlike Mitotic Prophase, members of each homologous chromosome synapse and crossing over (i.e. recombination) occurs

18. II. Mitosis and Meiosis alignment of tetrads is random, resulting in random separation of dyads. This is the basis for the Mendelian postulate of independent assortment. a single centromere holds the sister chromatids together. It does not divide during Meiosis I. The separation of homologous chromosomes during Anaphase I is referred to as disjunction Meiosis I

19. II. Mitosis and Meiosis The products of Meiosis I are two cells, each with a pair of recombined homologous chromosomes. Each pair is referred to as a dyad. The two chromosomes that make up the pair are also referred to as sister chromatids. The products of Meiosis II are four cells (two cells from each of the cells produced by Meiosis I), each with a single recombined chromosome. These chromosomes are referred to as monads.

20. II. Mitosis and Meiosis The development of gametes varies during spermatogenesis and oogenesis In humans, the first division of all oocytes begins in the embryonic ovary, but arrests in Prophase I. Meiosis resumes just prior to its ovulation.