Slide 110.1 An Inherited Hemoglobin Variant Causes Sickle Cell DiseaseThe First Patient with Sickle Cell DiseaseSlide 4Symptoms of SCDHemoglobin StructureThe Globin GenesGlobin Gene MutationsCause of Sickle Shape in Red Blood CellsIndividuals Heterozygous for the Mutant GeneSlide 11Gel ElectrophoresisThe Technique of Gel ElectrophoresisMaterials for Gel ElectrophoresisParameters of Separation of Molecules in the GelGlobin Protein Variants Can Be Separated by Gel ElectrophoresisSlide 17The Use of DensitometryHemoglobin Peptide Fingerprint AnalysisChromatographySlide 21The Nature of the SCD MutationIdentification of DNA Sequence VariationSingle Nucleotide PolymorphismsAdditional Approaches to SNP IdentificationRestriction Fragment Length PolymorphismsSlide 27Slide 28Slide 29Slide 30General Properties of Restriction EnzymesSlide 32RFLPs and SNPsMolecular ProbesGeneral Protein StainsInnovations in Gel ElectrophoresisDevelopment of Molecular ProbesElectrophoretic Analysis of Sickle Cell DiseaseSouthern Blot Analysis of -Globin VariationSlide 40Western Blot Analysis of -GlobinSlide 42Variant Globin GenesMalaria As an Agent of Natural SelectionMalaria InfectionHeterozygous AdvantageHeterozygote Advantage and Equilibrium FrequencyImportant Findings about Heterozygote AdvantageEvolution of  C and  E C and  ESlide 51Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachCHAPTER 10The Integration of Genetic Approaches: Understanding Sickle Cell DiseaseCopyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach10.1 An Inherited Hemoglobin Variant Causes Sickle Cell Disease2• Sickle cell disease (SCD), also called sickle cell anemia, has been intensively studied for more than a century.• SCD is potentially fatal.•Autosomal Recessive Disorder.• Caused by a structural abnormality in hemoglobin (Hb) that affects its ability to carry oxygen.•There are hundreds of variant hemoglobin alleles worldwide.• SCD variant is just one.Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachThe First Patient with Sickle Cell Disease•Walter Noel, a man of African origin, was the first person to be identified with SCD in New York in 1904. •The physician who first examined him was Ernest Irons.•Irons examined a blood sample from Noel and observed that many of the red blood cells had a peculiar shape, elongated shape.3Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachThe Disorder Was Named for the Unusual Deformity of the Red Blood Cells•Noel recovered from the initial bout of the illness, but died nine years later.•In 1910, James Herrick, who supervised Ernest Irons, published a paper describing the case-this was the first clinical description of SCD.•The disease was named “sickle cell anemia” a few years later.4Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachSymptoms of SCD5•SCD patients experience severe muscle pain when the sickle-shaped blood cells in their circulation are numerous enough to impeded blood flow in smaller vessels. • Reduced blood flow deprives surrounding tissues of oxygen, causing pain and long-term damage. •Sickled red blood cells are easily damaged and are removed from the circulatory system, and often cannot be replaced and quickly enough, leading to chronic anemia.Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachHemoglobin Structure6•Hemoglobin molecules are tetramers with two protein chains with 2 different globin genes, a- and b- globin This arrangement is the most common form and is called hemoglobin A (HbA).•Each protein in Hb carries one iron-containing molecule of heme, which reversibly binds to oxygen and pick up carbon dioxide.Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachThe Globin Genes•The a- and b-globin genes are members of a group of genes with strong structural & functional similarity.•The genes are organized similarly with 3 exons (coding regions) and 2 introns (spacing regions).•The a-globin gene encodes a protein 141 amino acids long; the b-globin encodes one 146 amino acids long.7Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachGlobin Gene Mutations8•At present, nearly 500 different allelic variants of a- and b-globin genes are known.•Nearly all are rare; some exist in just one family line.•More common variants have been well studied and provide examples of some hereditary processes.•SCD is a common hereditary anemia caused by a single base-pair substitution in the b-globin gene.•The mutant allele is called b S, while the normal allele is called b A •Individuals with SCD carry two b S alleles and so have genotype b S/b SCopyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachCause of Sickle Shape in Red Blood Cells9•When two abnormal b-globin proteins join two normal a-globin proteins, the hemoglobin molecules are structurally and functionally abnormal.•The instability of the abnormal hemoglobin molecules can cause them to collapse into linear crystal-like molecules.•This causes the deformation of the red blood cells into the characteristic deformed shape.Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachIndividuals Heterozygous for the Mutant Gene10•Individuals heterozygous for the mutation (carriers of SCD) have genotype b S/b A•Some of their hemoglobin molecules carry defective b-globin proteins.•Because most of their red blood cells are normal, they do not develop anemia. •They are sometimes identified as having sickle cell trait because they may have mild symptoms.Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach10.2 Genetic Variation Can Be Detected by Examining DNA, RNA, and Proteins11•There are numerous molecular genetic techniques available to researchers.•Some of them have been used to analyze the b S and b A alleles•Some can be applied to various types of DNA sequence variation.Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachGel Electrophoresis•In 1949 James Neel used transmission genetic analysis to demonstrate that SCD is a recessive disorder.•The same year, Linus Pauling and colleagues published the first molecular description of SCD and used the term molecular disease to describe it.•They