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

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

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

Somatic vs. Reproductive Cells REPRODUCTIVE CELLS (GAMETES) Female gametes: eggs (ova) Male gametes: sperm Characteristics Haploid 1 copy of each chromosome e.g.) Humans = 23

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

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

The Cell Cycle Centrioles replicate

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.

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

4 Phases of Mitosis Prophase Metaphase Anaphase Telophase

Interphase

Prophase Early centrioles

Prophase late

Metaphase

Anaphase

Telophase

Cytokinesis cleavage furrow

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

Difference between Meiosis and Mitosis

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

Stages of Meiosis Meiosis I and Meiosis II 4 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

Meiosis I Interphase Prophase I Metaphase I Anaphase I Telephase I

Meiosis II Prophase II Metaphase II Anaphase II Telephase II

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

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

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

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

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

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

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

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