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Unformatted text preview: Genetics and Evolution Pamela Diggle ([email protected]) Office: Ramaley C287 Office hours: Thursday and Friday 1-2 or by appointment INTRODUCTORY MATERIAL An example of the genetics and evolution of two inter-related diseases Sickle cell disease is a form of anemia It is the most common inherited blood disorder in the US It affects 72,000 Americans It affects 1 in 500 African Americans Fig 5.21 Sickle-cell disease. These sickled cells become stuck in small blood vessels, causing a "crisis" of pain, fever, swelling, and tissue damage that can lead to death. Capillary with red blood cells: www.tigr.org/tdb/ edb/pfdb/disease.html Fig 5.21 Sickle-cell disease and hemoglobin structure • Single amino acid substitution in one protein of hemoglobin • Causes cell to “sickle” and reduces oxygen carrying capacity Fig 17.23 Sickle-cell disease is caused by a single mutation Why does sickle cell persist in human populations? The distribution of the sickle cell gene coincides with the distribution of malaria Malaria is caused by a plasmodium parasite The parasite is carried by the female anopheles mosquito Each year 400 million people contract malaria About 2-3 million of these die from the disease Most malaria fatalities are children The sickle cell gene confers resistance to malaria! Humans carry two copies of each gene SS are susceptible to malaria Ss are resistant to malaria and slightly anemic Ss have sickle cell disease Most survivors are carriers When carriers have children All three genotypes are produced Fig 23.13 The sickle cell gene is maintained by stabilizing selection ON TO MITOSIS Chapter 12--Mitosis and the Cell Cycle Read page 218 to 223 and pages 232-233 Review the Summary of Key Concepts on page 234 for section 12.1 and 12.2 Self-quiz (page 234): 3, 4, 9, 10, 11 From this lecture you should know: What the cell cycle is and what occurs during each of the phases of the cell cycle The stages of the mitotic phase and the defining features of each stage The end products of mitosis and cytokinesis The difference between a chromatid and chromosome Two types of nuclear division Mitosis Products are genetically identical Same number of chomosomes Same genes Produces somatic cells Meiosis Products are genetically different One half the number of chromosomes Different complement of genes Produces gametes Mitosis and meiosis are usually followed by cytokinesis, the division of the cytoplasm Mitosis + cytokinesis + cell enlargement = growth in multicellular organisms Mitosis + cytokinesis + cell enlargement = reproduction in unicellular organisms Fig 12.5 Mitosis is part of the somatic cell cycle Mitosis and cytokinesis = the mitotic phase The mitotic phase alternates with interphase Interphase is divided into three subphases G1 = Gap 1--cell growth, biosynthesis S = synthesis phase--DNA synthesis, duplication of chromosomes G2 = Gap 2--cell growth, biosynthesis Differentiation Cell cycle ceases. Cell becomes specialized for particular function (liver, kidney, etc.) DNA duplication occurs during S phase Chromosomes are long strands of DNA There are usually multiple chromosomes in a eukaryotic cell Each chromosome exists as a long strand of DNA Following duplication of a chromosome, it exists as two chromatids closely attached to each other Chromatids are tightly attached to each other at the centromere Fig 12.6 G2 of interphase Cell enters G2 with 2X the amount of DNA Each chromosome has been copied exactly Each chromosome consists of two chromatids Chromosomes not condensed Nucelar envelope is intact Fg 12.6 Prophase DNA begins to condense by coiling Each chromosome still consists of two chromatids Mitotic spindle forms from microtubules Fig 12.4 DNA duplication occurs during S phase Condensation begins in prophase Condensation is completed in prometaphase Fig 12.6 Prometaphase Nuclear envelope fragments Chromosomes fully condensed Centrosomes at poles Some microtubules extend from poles of the cell toward equator Some microtubules attach to chromosomes Mitotic spindle consists of microtubules attached to chromosomes and some not attached Fig. 12.6 Metaphase Nuclear envelope is completely gone Chromosomes at equator = metaphase plate Fig. 12.7 Metaphase What it really looks like under a light microscope Fig. 12.6 Anaphase Chromatids separate One chromatid from each pair moves to opposite pole=>Genetic material is equally distributed Each chromatid is a chromosome as soon as it separates from its sister Fig 12.6 Telophase and Cytokinesis Telophase Nuclear envelope forms around the chromosomes at each pole Chromosomes less condensed Two new genetically identical nuclei! Cytokinesis Division of the cytoplasm Differs in plants and animals Two new cells! Fig 12.6 Review Fig. 12.5 In multicellular organisms most cells will eventually stop dividing and differentiate Fig. 12.19 Some cancers occur when control of the cell cycle is lost ...
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This note was uploaded on 04/09/2008 for the course EBIO 1050 taught by Professor Basey,john during the Fall '08 term at Colorado.
- Fall '08