1. Lab 8: Mitosis, Meiosis, and Chromosomes
Rationale:
We will investigate the processes wherein cells produce genetically identical daughter cells and the mechanisms of heredity and variation within organisms

2. Purpose of Lab 8 exercises:
ID stages of mitosis and meiosis
Locate the stages of mitosis on an onion root tip
Find and describe the stages of meiosis in lily anthers
Describe polytene chromosomes isolated from Drosophila

3. Somatic vs. Reproductive Cells
SOMATIC CELLS Are all body cells except reproductive cells
Characteristics
Diploid
2 copies of each chromosome e.g. Humans: = 46

4. Somatic vs. Reproductive Cells
REPRODUCTIVE CELLS (GAMETES) Female gametes: eggs (ova) Male gametes: sperm
Characteristics
Haploid copy of each chromosome e.g.) Humans = 23

5. Chromosomes and Genes
Chromosome Long strand of DNA and associated proteins
Chromatin Complex of DNA and protein
Gene Discrete unit of heredity Specific nucleotide sequence
Locus Physical location of a gene on a chromosome

6. MITOSIS Biological significance:
The common mechanism in eukaryotes for partitioning the genetic material equally at cell division.

7. The Cell Cycle
Centrioles replicate

8. The Cell Cycle Interphase- 75% of cell life cycle G1: rapid growth
S: DNA replicates ; centrioles replicate.
G2: cell prepares for cell division; microtubular structures form.

9. The Cell Cycle Cell Division
Mitosis: cell divides its nuclear components (chromosomes).
Cytokinesis: cell divides its cytoplasmic components.

10. 4 Phases of Mitosis
Prophase
Metaphase
Anaphase
Telophase

11. Interphase

12. Prophase
Early
centrioles

13. Prophase
late

14. Metaphase

15. Anaphase

16. Telophase

17. Cytokinesis
cleavage furrow

18. Experiment 1: Mitosis in the Onion Root Tip
Examine onion root tip
Identify the 4 different phases of mitosis
Region with high cell division
Root tips:
Useful because cells are frequently dividing
Use the very tip of the root
Apical meristem
Root cap

19. Difference between Meiosis and Mitosis

20. Meiosis Follow behavior of chromosomes through sexual cycles
Makes gametes haploid
Gametes only cells in human body not produced by mitosis

21. Stages of Meiosis
Meiosis I and Meiosis II stages leading up to the cell divisions These stages are called prophase, metaphase, anaphase, and telophase
Prophase I Prophase II
Metaphase I Metaphase II
Anaphase I Anaphase II
Telophase I Telophase II

22. Meiosis I
Interphase
Prophase I
Metaphase I
Anaphase I
Telephase I

23. Meiosis II
Prophase II
Metaphase II
Anaphase II
Telephase II

24. Meiosis: Prophase I & Metaphase I
Chromatin condenses into discrete chromosomes
Homologous chromosomes pair up—crossing over can occur: genetic diversity
Chromosomes align on the metaphase plate as homologous pairs
Spindle fibers from each pole attach to one chromosome of each homologue
Metaphase plate
Spindle fibers

25. Meiosis: Anaphase I
The 2 chromosomes of each homologous pair separate Move toward opposite poles
Haploid
The chromosomes moved to opposite poles
Cytokinesis separates the cytoplasm into 2 daughter cells
Each cell is haploid

26. Meiosis: Prophase II The chromatin again condenses into chromosomes
The chromosomes align on the metaphase plate

27. Meiosis: Anaphase II
Sister chromatids separate Move toward opposite poles Sister chromatids are now individual chromosomes
Haploid
Nuclei begin to form at opposite poles Cytokinesis occurs
4 Haploid daughter cells

28. Experiment 2: Meiosis in the Lily Anther
Today: Look at prepared slides of Lily Anther Male reproductive organ where meiosis occurs Pollen grains (gametes) are haploid
Very thin cross-section of stained lily anther

29. Meiosis in the Lily Anther
Each anther contains 4 pollen sacs
Look at cells in pollen sacs Pollen grains will be in different stages of meiosis

30. Experiment 3: Polytene Chromosomes of Drosophila
Today: Examine prepared slides of polytene chromosomes found in Drosophila melanogaster (fruit fly)
Located specifically in:
The gut.
Malphigian tubules (excretory organs) of larvae.
Footpads of adults.
Salivary glands of larvae

31. Polytene Chromosomes of Drosophila
Giant chromosomes
Have undergone many rounds of DNA duplication without cell division
Large size
Easily visible under the compound light microscope
Amenable for various genetic studies