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BIOL 205
Ian D Chin- Sang

BIOL205:week 5, lecture 14 The colors of peppers are determined by the interaction of several genes Nature of Mutations (alleles) • wt: no change, or the wild-type sequence (100% function) • intermediate: partial loss of function eg. a change in an amino acid that is not too important for the protein ◦ it can still fold up and function but may not function at 100% • null: complete loss of function of the protein. eg. a deletion of the gene, a change in crucial amino acid, a truncated protein because of an early stop codon (0% function) • most null alleles lead to recessive phenotypes: • +/null = “wild-type” • null/null= mutant Why? Because most genes are haplosufficient, one copy is good enough Null mutations of haplosufficient genes are recessive • Null mutations of haploinsufficient genes are Dominant (rare). • +/null = mutant phenotype • why? because one good copy of the gene is not good enough. • Q. Can you get Dominant mutations in haplosufficient genes? ◦ Yes, but these are not caused by null alleles. • These are special mutations— “dominant gain-of-function alleles” → Muller, H. J. 1932. Dominant mutations in haplosufficient genes: null • normally a haplosufficient gene : +/D = wild-type • but some rare dominant alleles (D ) in the same gene • will give a mutant phenotype: +/D = mutant phenotype • hypermorph (overactive function): eg. mutation that stabilizes the protein, or causes an enzyme to be always active (> 100% function) • many oncogenes are hypermorphic alleles (ex: genes says when to divide, increases promoter affinity, etc.) Antennapedia “antenna foot” Antennapedia is a transcription factor which controls the placement of legs → promoter “on inappropiately” • reason for this happening: jumping gene, • but it turns out antennapedia: region flipped and lost its promoter and now is under control of promoter that drives the expression in the head • +/null: wildtype • null/null: instead of leg → antenna • antennapedia: role is to block antenna to come out of second thoraxic segment • Neomorph (novel function) ◦ eg. amutation in a gene such that it is expressed at a different time or tissue • for example a gene under control of a new promoter. eg.Antennapedia • Antimorph (dominant negative):Amutation that makes a spoiler product: eg. proteins that normally function as dimers or in a protein complex Two models for dominance of a mutation Dominant negative mutation:dominant b/c one dose ofmutationmeans proteindoesn't work (poison) → DOM Dominant negative (DN) mutations in collagen Collagen trimer - Osteogenesis Imperfecta (OI C. elegans R
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