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BIOS 2011 Lab 3 Mitosis and Meiosis

BIOS 2011 Lab 3 Mitosis and Meiosis - Exercise 3 Mitosis...

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Exercise 3 Mitosis & Meiosis 27 MITOSIS AND MEIOSIS in Alium cepa (onion) root tip and Lilium longiflorum (Asiatic lily) anther Learning Objectives: 1. To learn about the process of mitosis. 2. To learn about the process of meiosis. 3. To learn how to prepare slides of onion root tips and meiocytes from lily anthers for observation using a compound microscope. 4. To become familiar with (and respectful of) the use of a compund microscope. 5. We'll be extracting DNA from your ants and running the PCR reactions. Read the procedure for those steps in the PCR lab. (Lab 5) Readings: Hillis, Sadava, Heller, and Price, Principles of Life , 2012. Pages 132-139. Appendix C, Use of the Light Microscope. Assignment: You will be provided with a worksheet to collect data and record your observations during the lab; this assignment is to be completed and turned in before you leave. There will also be a 10-point identification quiz at the end of the lab. PART ONE: MITOSIS IN ONION ROOT TIPS INTRODUCTION The Karyotype The cells of all eukaryotic organisms exhibit a species-specific genome . That is, all conspecific individuals share equivalent sets of genes , which exist in alternate forms called alleles . Simply defined, a gene is a sequence of DNA that codes for a polypeptide. Genes are organized into chromosomes , which are comprised of DNA and various proteins known as histones and non-histones. This nuclear genetic material is sometimes referred to as chromatin because it can be recognized with certain stains. The number of chromosomes is the same for all members of a particular species. At certain stages of cell division chromosomes can be distinguished one from another by identifiable characteristics such as length and position of centromeres. A complete description of
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Exercise 3 Mitosis & Meiosis 28 the number and kinds of chromosomes present in a eukaryotic cell is referred to as the karyotype of that species. Haploidy and Diploidy The term ploidy refers to the number of sets of chromosomes present in a cell; a rule of thumb is to count centromeres to determine ploidy number. Most of the cells that make up an organism, the somatic cells , are diploid . In other words, they are 2N; they contain two complete sets of chromosomes, two copies of each gene. Each chromosome of one set is matched by another chromosome in the other set; the chromosomes of such a pair are called homologous chromosomes , or homologues . Ultimately, each set of chromosomes, each homologue, is derived from one of the individual's parents. Other cells of the organism are involved with sexual reproduction and are haploid (1N). These are the gametes. There is a halving of the chromosome number so that there is only one complete set per cell. Each type of chromosome within the cell is without a homologue. This will be addressed further in the discussion of meiosis.
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