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Lab 8: Mitosis, Meiosis, and Chromosomes

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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

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