CHROMOSOMES, MITOSIS, MEIOSIS, AND MENDELIAN GENETICS MODULE 8:

MODULE 8: PART I Chromosomes and Mitosis

Objectives After completing this lab topic you should be able to : After completing this lab topic you should be able to :  Describe the activities of chromosomes, centrioles, and microtubules in the cell cycle, including all phases of mitosis.  Describe differences in mitosis and cytokinesis in plant and animal cells.

MITOSIS: A process of cell (nuclear) division characterized by a sequence of distinctive stages that conserve chromosome numbers by equally allocating replicated chromosomes to each of two daughter cells, occurring in somatic cells.

CHROMOSOMES: CHROMOSOMES:  Long, threadlike associations of genes found in the nucleus of all eukaryotic cells and most visible during mitosis and meiosis. Chromosomes consist of DNA and protein.

Ploidy (N): Term used to describe the number of chromosomes of a certain type. Most organisms are DIPLOID (2N), which means their chromosomes occur in pairs; for example a human has 46 chromosomes OR 23 pairs of chromosomes, (N=23; 2N=46). Polyploidy: A chromosomal alteration (e.g, mutation) in which organism possesses more than two complete chromosome pairs. (i.e., TRIPLOID (3N), TETRAPLOID (4N), etc.).

THE CELL CYCLE: An ordered sequence of events in the life of a dividing cell, composed of the G1, S, G2, and M. G1. S, and G2 are collectively called as Interphase (I). The MITOTIC PHASE (M) consists of MITOSIS (KARYOKINESIS = division of nucleus) and CYTOKINESIS = division of cytoplasm.

1. PROPHASE: In nucleus -nucleolus dissappear. -each duplicated chromosome appear as two identical sister chromatids joined at the centromere. In cytoplasm -the centrosome moves away from each other. -the spindle fibers attach to the chromosomes at kinetochore site of the centromeres.

2. METAPHASE: -the centriole pairs are now at opposite ends, or poles, of the cell. -chromosomes are aligned with one another at the equatorial (the metaphase plate) of the cell.

. ANAPHASE: -each chromatid (now is considered as a full- fledged chromosome) move towards the opposite poles. -by the end of this phase, the two poles have equivalent and complete collections of chromosomes.

4. TELOPHASE followed by CYTOKINESIS: - chromosomes gather at the two poles. - nuclear envelopes are formed in this process which is followed by cytokinesis or division of cytoplasm which result in formation of two daughter cells that have same number of chromosomes.

CYTOKINESIS: 1). Animal type cytokinesis: - occurs by process called cleavage. - a contractile ring, pinch the parent cell to form cleavage furrow that becomes deep and pinch the two daughter cells away. 2). Plant type cytokinesis: - no cleavage furrow. - occurs by formation of cell plates across the midline of the parent cell. - the cell plates fuse together and separate the two daughter cells.

Example of Mitosis in a plant cell:

Example of Mitosis in an animal cell:

Today’s lab will entail the following: Lab exercise to mimic mitosis using pipe cleaners and beads (handout). Lab exercise to mimic mitosis using pipe cleaners and beads (handout).