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Human Genetic Disorders Autosomal Recessive Sickle-cell disease

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Human Genetic Disorders Autosomal Recessive Sickle-cell disease Single amino acid substitution (valine for glutamate) in hemoglobin Causes some erythrocytes to form sickle shape Abnormal erythrocytes slow blood flow and may block capillaries. Human Genetic Disorders Autosomal Recessive - PowerPoint PPT Presentation

Text of Human Genetic Disorders Autosomal Recessive Sickle-cell disease

  • Human Genetic Disorders

    Autosomal RecessiveSickle-cell diseaseSingle amino acid substitution (valine for glutamate) in hemoglobinCauses some erythrocytes to form sickle shapeAbnormal erythrocytes slow blood flow and may block capillaries

  • Human Genetic Disorders

    Autosomal RecessiveSickle-cell diseaseSingle amino acid substitution (valine for glutamate) in hemoglobinCauses some erythrocytes to form sickle shapeAbnormal erythrocytes slow blood flow and may block capillariesMost common in people of African descent (1 in 10 African Americans is heterozygous sickle cell trait)Why so common?May be advantageous in areas where malaria is a problemHeterozygous people more resistant to malaria than homozygous dominant people

  • Fig. 23.17

  • http://upload.wikimedia.org/wikipedia/commons/1/10/Malaria_versus_sickle-cell_trait_distributions.png Malaria Sickle Cell Allele Frequency

  • http://www.cdc.gov/malaria/about/biology/sickle_cell.html

  • Human Genetic Disorders

    Autosomal RecessiveTay-Sachs diseaseAbsence in brain of enzyme that helps to break down membrane lipids and prevents their accumulationAccumulation causes brain damageEspecially common in people of Ashkenazi Jewish (Eastern European) descentPossibly due to population bottleneck during persecution & restriction to ghettos in Middle Ages

  • Human Genetic Disorders

    Autosomal DominantAchondroplasiaAbnormal gene on chromosome 4 skeletal growth disorder dwarfism (relatively normal torso, short arms and legs)Most common growth-related disorderResults from inheritance in

  • Chromosomal Theory of Inheritance

    Proposed in early 1900sUnified understanding of mitosis and meiosis with Mendels work on inheritance

  • Fig. 15.2

  • Linkage and Recombination

    LinkageAlleles dont always assort independentlyTwo genes on same homologous chromosomeLinkage first studied in Drosophila by Thomas Morgan (early 1900s)Worked with wild type and mutant fruit fliesStudied inheritance with two-point test cross between heterozygous individual and homozygous recessive individual

  • Fig. 15.9

  • Linkage and Recombination

    RecombinationOccurs during crossing over in meiosisDrosophila exampleF1 parent produced some recombinant gametes

  • Fig.15.10

  • Linkage and Recombination

    RecombinationGreater distance between genes Greater probability of recombinationDistance between two genes expressed in map units1 map unit = 1% recombination frequency

  • Fig. 15.11

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