Introduction What is Genetics? What level of organization is being examined? –molecular, cellular, species, or population What is the purpose of this lab?
Somatic versus Reproductive Cells Somatic cells: –all except the reproductive cells –2 copies of each chromosome –diploid –example: in humans, the diploid number is 46 Reproductive or sex cells: –haploid –1 copy of each chromosome
Nuclear Division Mitosis –prior to mitosis chromosomes are duplicated –nuclear division in somatic cells –genetic info from parent to daughters –cancer: uncontrolled cell division
Nuclear Division Meiosis –prior to meiosis: chromosomes are duplicated – nuclear division in the sex cells –genetic diversity
Cytokinesis division of the cytoplasm occurs at the end of mitosis occurs at the end of meiosis I occurs at the end of meiosis II
Interphase no nuclear or cell division DNA replication, chromosome duplication, and cell growth chromosomes, not visible inside nucleus but can see nucleolus inside nucleus
Mitosis Four phases of mitosis: –prophase –metaphase –anaphase –telophase End result of mitosis: 2 daughter cells
Prophase Duplicated chromosomes condense and become visible as sister chromatids joined at the centromere nuclear membrane disintegrates; neither the nucleus nor the nucleolus is distinct spindle apparatus of the cell is formed
Early prophase Prophase Chromatin condenses into discrete chromosomes –two identical sister chromatids –joined at the centromere
Metaphase Chromosomes are aligned along the cells equator at their centromeres spindle fibers are visible
Metaphase Chromosomes convene on the metaphase plate, an imaginary equator located between the two poles of the spindle. Centromeres are aligned, and sister chromatids of each chromosome straddle the metaphase plate. Metaphase plate Spindle fibers
Anaphase Migration of the chromosomes: –centromeres split –move along the spindle fibers towards opposite poles –pulling the sister chromatid Each chromatid -- a chromosome
Anaphase The sister chromatids separate from each other and move along the spindle fibers towards opposite poles. Each chromatid is now considered a chromosome. Early anaphase Anaphase Spindle poles
Anaphase Late anaphase By the end of anaphase, each pole has an equivalent and complete set of chromosomes.
Telophase Chromosomes are aggregated at the poles and begin to thin out and extend in length new nuclear membrane forms; nucleolus and nucleus begin to reappear spindle disintegrates cytoplasm divides (cytokinesis occurs); daughter cells begin to form
Telophase Late telophase Cytokinesis begins, separating the cytoplasm into 2 daughter cells. Telophase The daughter nuclei begin to form at the two poles Nuclear membranes begin to form chromosomes lose their distinct appearance.
Daughter Cells Telophase formation of 2 daughter cells Each daughter cell has same genetic material as parent
Meiosis: Reproductive or Sex Cells Gametes – female gametes: eggs or ova (ovum, singular) – male gametes: sperm – HAPLOID, have 1 copy of each chromosome (i.e., 1/2 as many chromosomes as somatic cells) – example, in humans, the haploid number is 23.
Meiosis in the Lily Anther Lily anther: –male reproductive organ in flowering plants. –meiosis takes place –result: haploid pollen grains
Meiosis in the Lily Anther A very thin cross-section of a lily anther stain it examine with a compound light microscope:
Meiosis in the Lily Anther Each anther contains 4 pollen sacs where meiosis takes place.
Meiosis in the Lily Anther Study the various phases of meiosis in prepared slides of the lily anther. look at the cells inside the pollen sacs locate the different phases.
Stages of Meiosis Meiosis consists of meiosis I and meiosis II and both have 4 stages leading up to the actual cell division. Meiosis I:Meiosis II: Prophase IProphase II Metaphase IMetaphase II Anaphase IAnaphase II Telophase ITelophase II
Meiosis: Prophase I Chromatin condenses into discrete chromosomes. Chromosome is actually composed of 2 sister chromatids. Homologous chromosomes come together as pairs.
Meiosis: Metaphase I Metaphase plate Spindle fibers Chromosomes are arranged on the metaphase plate, still in homologous pairs. Spindle fibers from each pole attach to one chromosome of each pair of the homologue.
Meiosis: Anaphase I each homologous pair of chromosomes separate and move toward opposite poles. each chromosome still consists of 2 sister chromatids joined together at the centromere.
Meiosis: Telophase I Haploid Chromosomes have moved to opposite poles. Cytokinesis separates the cytoplasm into 2 daughter cells. Each cell is now haploid.
Meiosis: Prophase II In prophase II, the chromatin again condenses so the chromosomes have a distinct shape.
Meiosis: Metaphase II In metaphase II, chromosomes align on the metaphase plate.
Meiosis: Anaphase II sister chromatids separate, and move towards opposite poles sister chromatids are now individual chromosomes.
Meiosis: Telophase II Haploid nuclei begin to form at opposite poles, and cytokinesis occurs 4 daughter cells, each with the haploid number of chromosomes.
Meiosis I: Review Prophase IMetaphase I Telophase I Anaphase I
Review: Meiosis II Prophase IIMetaphase II Anaphase IITelophase II
Chromosomes and Genes one long strand of DNA associated proteins –chromatin thousands of genes gene –discrete unit of heredity locus –physical location of a gene
Homologous Chromosomes, Genes, and Alleles Chromosome pair: –homologous chromosomes pair has genes at the same loci – alleles –may be the same or different
Human Genetics Genotype –heterozygous –homozygous Phenotype Observe traits and identify which form you possess Make a table
Extra 21st chromosome Heredity and Genetic Disorders Video, Healthy, Heredity, and Genetic Disorders
Mechanics of Mitosis Answer questions –use instructional materials available video: Mechanics of Mitosis posters Photo Atlas of Biology
Mitosis in the Onion Root Tip Todays lab exercises –examine the tip of an onion root –find and identify the 4 different phases of mitosis. Root tips are useful material because the cells are frequently dividing as the root grows.
Growth and Mitosis in Onion Root Tips A) Examine onion (Allium) root tip under low power objective (10x) –answer questions B) Examine same slide under high power objective (40x) –follow instructions
Meiosis: The basis of Genetic Inheritance and Sexual Reproduction Mechanics of Meiosis –Answer questions use instructional materials available –video: Mechanics of Meiosis –posters –Photo Atlas of Biology
Meiosis and Gamete Formation in Lily Anthers Observe first and second meiotic division in demonstration slides Note: DO NOT move the slides out of position Use only FINE focus