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Chapter 6-2.docx

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BIOL 2000
Joseph Rasmussen

Chapter 6-2 Lethal Alleles  Causes death of the individual when homozygous  When heterozygous they can still live.  The death is usually not noted as it creates an assumption.  Changes the Mendel 1:3:1 ratio to a 1:2 ratio o Ex. Yellow coat in mice is a recessive lethal allele  Yellow x yellow = 1black: 2 yellow: 1 death o Ex. Tailless, a recessive lethal allele in cats L  M / M= tailless  M /M = lethal Questions 7,8,10,11,12,13,14 Interactions of genes in pathways  Objective 3: Understand how Beadle and Tatum’s experiments led to the idea that multiple genes may control multiple steps in a biosynthetic pathway  Archibald Garrod o Connected a genetic defect to a defect in chemical reactions in the body  George Beadle and Edward Tatum o One-gene-one-enzyme (polypeptide) model o Isolated arginine auxotrophs in Neuspora o Auxotoph- strain bale to grow only on supplemented media o Prototoph (wild type)- able to grow on minimal media o First xrayed to make mutants. Then wild type cross with wild type of opposite mating type grew into fruiting bodies and into microscopic ascospores that were dissected and transferred one by one to culture tubes. o Plated onto:  Mutagenized spores transferred to complete media, then moved to  Asexual spores transferred to minimal media  No growth on minimal media identifies nutritional mutant (if it grew on complete media)  Auxotrophs that cannot grow, tested for growth on various media  To try and figure out the specific mutation that lead to the inability to grow.  If it can grow when given amino acids, that is the issue.  Then put it on the various amino acids to see what helps. o If it can gr
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