Rare exception 1haploinsufficiency tt because half the

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Unformatted text preview: exception #1—haploinsufficiency tt • because half the amount of protein is insufficient, the mutant acts as a dominant → alleles designated t, T TT wild type short tail mutant threshold amount of functiona l “t” protein genotype: normal tail short tail tt Tt TT rare exception #2—no threshold e.g., snapdragon flower color CR: enzyme that makes red pigment Red CRCR x Pink CRCI Ivory CICI Amount of red pigment CI: no enzyme activity no threshold! Genotyp CRCR CRCI CICI e: heterozygote has intermediate phenotype… this is called incomplete dominance rare exception #3—“poisonous” subunits …also called dominant-negative mutations Amount of active protein threshold aa Aa AA why does Aa have so little activity? “wt” phenotype “mutant” phenotype example: “poisonous” subunits alleles: protein subunits: assembled enzyme: phenotype: wild type mutant heterozygote has mutant phenotype Main Symptoms: • tall • long narrow face • long arms and legs • possible problems with other organs example: Marfan syndrome (some forms) result from a dominant-negative mutation in the fibrillin 1 (FBN1) gene ? http://www.marfansyndrome.info/; http://www.nps.gov/liho/history...
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