CONTENT I. Sexual and Asexual Reproduction

Transcription

1 Chapter 8 Cellular Reproduction: Cells from Cells Objectives: 1. Define any new terms related to cell division. 2. Use a table to compare and contrast mitosis and meiosis. 3. Use drawings to compare and contrast the different phases in mitosis and meiosis. 4. Use a drawing to describe the parts of a chromosome. 5. Define cancer and make a list of its characteristics. 6. Explain how sexual reproduction leads to species diversity. 7. List examples and consequences of deviations from the normal sex chromosome number. 8. Use a table to indicate the advantages and disadvantages of sexual and asexual reproduction. CONTENT I. Sexual and Asexual Reproduction II. The Cell Cycle III. Mitosis IV. Cancer Cells V. Meiosis: The basis of sexual reproduction. VI. Comparing Mitosis and Meiosis VII. Deviations from the normal chromosome number. I. Asexual and Sexual Reproduction A. Asexual: DNA is a single, circular chromosome attached to the membrane. Parent cell divides in half; offspring are genetic replicas of the parent cell because all the chromosomes come from a single parent. Observed in prokaryotic cells, in yeast ( budding ), and other eukaryotic singlecelled organisms, such as amoebas binary fission. B. Sexual: requires fertilization of an egg by a sperm. Somatic (any cell except egg & sperm), cells in the multicellular organism reproduce by mitosis for the purpose of growth and maintenance; gametes egg & sperm are produced by meiosis, which occurs in reproductive organs (ovaries and testes in humans). Eukaryotic DNA is found as free-floating linear chromosomes within the nucleus. The long, linear strand is wrapped around histones (proteins) forming nucleosomes. These keep DNA untangled, ordered, and in an efficient package. The end tips of the DNA are called telomeres. Chromatin condenses and forms a supercoil called the chromosome. Sketch a simple DNA molecule showing chromatin, chromosome, histones, nucleosome, and telomeres. II. The Cell Cycle A. Interphase: cell growth and preparation to divide 1. G1 (Gap 1): cell growth and maintenance (neurons and heart cells spend most of their time here). Appropriate environment trigger synthesis. Takes about 12 hrs. 2. Synthesis (S): every chromosome is copied by replication (see section below). Before replication, chromosomes are long & linear, after replication they are paired by holding Page 1 of 5

2 them near the center via the centromere (section of DNA that holds chromosomes together). Takes about 6 hrs. a) Unwinding: Unwind and separate DNA by specific enzymes b) Rebuilding: DNA polymerase adds complementary nucleotides to each template: A-T, C-G. This enzyme also proofreads and corrects mistakes. Sketch a replicated chromosome and label sister chromatids and centromere. 3. G2 (Gap 2): growth continues, preparation for division. Shorter than G1. Takes about 6 hrs. B. Mitotic phase (M): cell division (~30 min.): nucleus of parent cell duplicates followed by the cytoplasm and plasma membrane: cytokinesis (separation of organelles, cytoplasm, cell membrane). Checking: 1. Define telomere 2. What organisms go through binary fission and what organisms show mitosis/meiosis? 3. Describe how the DNA is found in prokaryotes and eukaryotes. What is the function of histones? 4. What is the difference between asexual and sexual reproduction? 5. Difference between somatic and sex cells 6. Define cell cycle. Describe the structure of a replicated chromosome. 7. Define DNA replication. Provide a brief description of the process, include DNA polymerase. III. Mitosis replaces worn-out old cells with fresh new duplicates. A. Process by which existing somatic cells generate new, genetically identical cells. Apoptosis: programmed cell death (especially those in the digestive tract and liver). B. Details of Mitosis: 4 steps: 1. Prophase: (preparation) nuclear membrane breaks down, sister chromatids condense, spindle fibers form. 2. Metaphase: (middle) sister chromatids line up in the middle of the cell 3. Anaphase: (apart) sister chromatid pairs are pulled apart by spindle fibers. 4. Telophase: (two nuclei) chromosomes uncoil as nuclear membrane is reassembled. C. Cytokinesis: cytoplasm and organelles have duplicated and are divided into equal two parts. Cell splits in two. Sketch & label the steps of mitosis as the cell comes from interphase. Briefly describe what happens at each step. Page 2 of 5

3 IV. Cancer Cells. Unrestrained cell growth and division caused by disruption on DNA to regulate division. Second cause of death in the US (heart disease is #1), more than 20% of all deaths. 1. Characteristics of cancer cells: loose contact inhibition and ignore high density signal; divide indefinitely (normal cells divide ~50 times) due to telomere rebuilding. Two kinds of tumors: Benign: cell mass that doesn t spread (moles, warts). Malignant: cells spread through circulatory system: metastasis, 2. How does it cause cell death? By pressure on neighboring tissues and disruption of vital processes. 3. Treatment: surgical removal or kill/slow down cell division. To kill or slow down: chemotherapy (more generalized damage) and radiation (more localized damage). These interfere with rapid cell division. 4. Side effects: reduced red blood cells shortness of breath & fatigue; reduces platelets and white blood cells increased bruising and infection; reduced hair follicle cell growth hair loss 8. Define apoptosis. 9. Describe the steps in mitotic division and identify them in a picture. 10. Define cancer and provide characteristics of cancer cells. 11. What is the difference between benign and malign tumors. How does cancer cause death? 12. Provide two side effects for cancer treatment. V. Meiosis: The basis for sexual reproduction: reduction of genome in half. A. Sexual Reproduction: fusion of 2 reproductive cells in fertilization. To avoid chromosome overload meiosis: process by which organisms make special reproductive cells, which have only half as many chromosomes as somatic cells. Diploid cells have 2 copies of each chromosome (i.e. 46 chromosomes in humans), whereas haploid cells have one copy (i.e. 23 chromosomes in humans). B. Human Life Cycle: 1. A sexually mature adult develops from a zygote. All trillions of somatic cells replicate through mitosis (46n) 2. Haploid (1n) gametes are produced in the gonads (ovaries produce eggs and testes produce sperm) during sexual maturity. 3. Fertilization of the egg produces a zygote (2n) that, through mitotic division in embryonic development, grows into a human baby. More mitotic division of somatic cells and meiotic division of gametes produce another sexually matured human being. C. Meiosis 1. Meiosis I: homologues separate a) Prophase I: chromosomes condense, spindle forms, crossing over of chromatids in homologues, nuclear membrane disintegrates (i.e. a bit of DNA from father is inserted into mom s chromosome). Crossing over doesn t create new alleles but it does create new combination of alleles on a chromatid, increases diversity. b) Metaphase I: Homologues line up at the center, random, independent assortment of homologues. c) Anaphase I: Homologues separate to opposite poles. d) Telophase I & cytokinesis: nuclear membrane reassembles, chromosomes may unwind slightly and cytoplasm finishes dividing into 2 daughter cells 2 diploid cells. 2. Meiosis II: sisters chromatids separate a) Prophase II: chromosomes in both daughter cells condense b) Metaphase II: sister chromatids line up at the center c) Anaphase II: sister chromatids separate to opposite poles Page 3 of 5

4 d) Telophase II & cytokinesis: nuclear membrane reassembles and cytoplasm finishes dividing in both cells. Total = 4 haploid cells. Sketch & label the phases of Meiosis I and Meiosis II and indicate where Crossing Over & Independent assortment occur. Meiosis I Meiosis II Progenitor cell, Diploid, 2N PI, Crossing over, Recombination MI, Homologues align in the middle, Independent assortment AI Homologues separate TI, New nuclei for new chromosomes Cyt PII, MII, AII TII & Cyt D. Benefits and Costs of sexual reproduction A. Benefits: Genetic variation through 1.crossing over (in prophase I), 2.random reassortment of homologues (in anaphase I), 3.alleles come from 2 parents. This variability enables populations of organisms to cope better with changes in the environment. In asexual organisms, this may be a disadvantage, as offspring is an exact copy of the parent cell. 4. Random fertilization: you are 1/64,000,000,000,000 (one in 64 trillion combinations!). 3. Costs: dangers associated with mating rituals (vulnerability, disease), it takes time and energy to find a partner, this energy may be used for reproduction by asexual organisms. 16. Define: meiosis, haploid, diploid, homologous chromosomes (aka homologues), sister chromatids. 17. Explain the process of meiosis by dividing it into meiosis I and II. Include terms like crossing over and random separation. Identify the location of haploid and diploid cells in the process. 18. How many haploid cells are produced through meiosis? How is this different from mitosis? 19. Provide 3 differences between male and female gametes. 20. How is genetic variation possible in sexual reproduction? Name 2 disadvantages of sexual reproduction. VI. Comparing Mitosis & Meiosis Specific for what type of cell? Purpose of cell division: Mitosis Meiosis Number of divisions: How chromosomes line up in metaphase (Mit) and metaphase I (Mei)? Diploid or Haploid parent cell? Diploid or Haploid daughter cells? Are daughter cells identical to parent cell? Are daughter cells identical to each other? How many daughter cells? Page 4 of 5

5 VII. Deviations from the normal chromosome number lead to problems Non-disjunction: homologous chromosomes fail to separate during meiotic I or meiosis II A. Abnormal number of autosomal chromosomes. Down syndrome: syndrome caused by non-disjunction of chromosome 21, aka trisomy 21; it affects 0.05% of children (<1/2000) born to women under the age of 30. First described in 1866 by Dr. John Langdon Down. The risk increases as the mother gets older (80/1000 for women at age 50). 1. Characteristics: learning disabilities, flat facial profile, heart defects, increased susceptibility to respiratory difficulties. Non-disjunction can occur during anaphase I or anaphase II 2. Risks: older females. As women age, their gametes tend to have more errors. Meiosis of her eggs began near the time the woman was born and they may not complete it until the age of 40 or more. In males, new sperm cells are produced every 2 weeks after puberty. B. Abnormal number of sex chromosomes. 1. Turner syndrome: XO, short size, ovaries don t mature, incomplete development of sex organs, some learning difficulties. Frequency 1/5000 births. 2. Klinefelter syndrome: XXY, develops as male, feminized, smaller testes, long limbs, language impairments. Frequency 1/2000 births. 3. Super males : XYY, taller than average, moderate to severe acne, slightly lower intelligence. Frequency 1/2000 births. 4. Meta females : XXX, may be sterile, no obvious physical or mental problems. Frequency 1/1000 births. 21.What are the factors that lead to genetic variation? 22. What does meiotic division achieve as compared to mitosis? 23.What are autosomal and sex chromosomes? 24. How is Down syndrome caused? 22. Provide 4 examples of mutations caused by the number of sex chromosomes. Answer questions 1-8, 10, on pages Homework : 6 points, Due: next meeting Chapter 9 1) Sketch Figure 8.15, page 134 to compare mitoses and meiosis. Use a white sheet of paper (use the whole sheet) and your color pencils. Write the description of each step as it is indicated in the textbook. 2) Define 10 new vocabulary words from chapter 9 on the back of the white sheet you used above. Pick those terms that present the highest difficulty to understand. Do YOUR best! Page 5 of 5