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Beyond Mendel, Sex Linkage, Human Genetics Mendel studied only simple inheritance WELL-DEFINED, DOM/REC Non-Mendelian Inheritance Patterns Incomplete Dominance: INTERMEDIATE HET (Rr = PINK) Homework - perform P, F1, F2 crosses USING SNAPDRAGONS Multiple Alleles: some genes have MORE THAN TWO ALLELES Understand: A, B, O BLOOD TYPING Phenotype Type A Type B Type O Type AB Genotype Understand: A, B, O BLOOD TYPING Phenotype Genotype Type A Type B Type O Type AB AA or AO Understand: A, B, O BLOOD TYPING Phenotype Genotype Type A Type B Type O Type AB AA or AO BB or BO Understand: A, B, O BLOOD TYPING Phenotype Genotype Type A Type B Type O Type AB AA or AO BB or BO OO Understand: A, B, O BLOOD TYPING Phenotype Genotype Type A Type B Type O Type AB AA or AO BB or BO OO AB Codominance: both alleles EXPRESSED/DETECTED (e.g. AB) Nature/Nurture: environment INFLUENCES PHENOTYPE Morgan, Flies, Sex Linkage - 1910s Genes Shown on Chromosomes By now, scientists could see CHROMOSOMES AND MEIOSIS Drosophila melanogaster: FRUIT FLY Autosomes (flies have 3 pairs): NOT GENDER DETERMINING Sex Chromosomes (flies have 1 pair): GENDER DETERMINING, X AND Y Wild Type: DOMINANT (e.g. RED EYES) Mutant: RECESSIVE (e.g. WHITE EYES) Cross 1: True Parentals RED FEMALE X WHITE MALE At first, Morgan assumed eye color was autosomal/Mendelian: F1 = Rr, F2 = 3:1 But F2 was half unexpected: where all females red, MALES 50:50 RED:WHITE Morgan formed a new hypothesis: GENE FOR EYE COLOR ONLY ON X Rule Three: For sex linkage, show alleles on X’s (e.g. XR) - none on Y’s. Prediction must include gender. Use Mendelian letters for genes - not Morgan’s (+/-) naming system. Let’s Show the P X P Cross to F1 P Gametes: red/female X white/male Let’s Show the P X P Cross to F1 P Gametes: red/female X white/male XR Xr Y XR Xr XR XR Xr XR XR Xr Y XRY XRY Predictions: 50% RED FEMALES 50% RED MALES Let’s Show the F1 X F1 Cross to F2 F1 Gametes: Het/Female X Red/Male Let’s Show the F1 X F1 Cross to F2 F1 Gametes: het/female X red/male XR XR Y Xr XR XR XR XR Xr Xr XR Y XR Y Xr Y Predictions: 50% RED FEMALES 25% RED MALES; 25% WHITE MALES Is this consistent with observations? Some Human Genetics Pedigree Analysis: MASTER ALL RULES Make sure you define shaded trait OR write phenotype below each person. The following FYI traits are NOT on exam. Gene Dom Allele Rec Allele Chin Dimple Free Ear Lobes Widow’s Peak Left Thumb Top Iris Pigmentation + + + + + - Sickle Cell Anemia • REC AUTOSOMAL - SOME INC DOM • African Americans - 1/400 • Carriers - 1/10 • Defective HEMOGLOBIN CHAIN • Hom/Rec = LETHAL; Het = WEAK Protects against tropical malaria - thus, selected among many equatorial races. Cystic Fibrosis • REC AUTOSOMAL • European Caucasions - 1/2500 • Carriers - 1/24 • Defective Na/Cl TRANSPORTER • High levels of secreted SALT, MUCUS • If untreated, LETHAL BY AGE 5 Huntington Disease • DOM AUTOSOMAL • Unstable - EXPANDING MUTATION • 30,000 HAVE, 150,000 AT RISK • Gene function unclear • Degenerative BRAIN FUNCTION • No good treatment - LETHAL 35-45 Duchenne Muscular Dystrophy • REC X-LINKED • Male Bias - 1/3500 • Defective anchoring protein between… • CYTOSKELETON AND MEMBRANE • Degenerative MUSCLE DISEASE • No good treatment - LETHAL 20-25
