Brooker_Chp5_MappingP - Chapter 5 Eukaryotic Gene Mapping...

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Chapter 5 Eukaryotic Gene Mapping
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Gene mapping / chromosome mapping - Historically, based on recombination events during meiosis Determine the linear order of linked genes within one chromosome Why bother ?? GENETIC MAPPING
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Allow an understanding of genetic organization and complexity Improve understanding of evolutionary relationships among species Useful in diagnosis, and perhaps, treatment of inherited diseases Helpful in predicting likelihood of specific trait inheritance - Human genetic diseases - Agricultural applications Genetic maps can be useful
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Each gene has its own unique locus at a particular site within a chromosome
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Establishing the distance between linked genes
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Map distance = Number of recombinant offspring Total number of offspring X 100 By convention 1 map unit = 1% recombination frequency 1 m.u. = 1 centimorgan (cM)
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Genetic mapping experiments are typically accomplished by carrying out a testcross Consider two linked genes affecting bristle length and body color in fruit flies e = ebony body color e + = gray body color s = short bristles s + = normal bristles One parent displays both recessive traits ( ss ee ) Second parent is heterozygous for the two genes Genes for s and e are linked (i.e., on one chromosome)
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Chromosomes are the product of a crossover during meiosis in the heterozygous parent Recombinant offspring are fewer in number than nonrecombinant offspring cis vs. trans allele arrangement
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Experimental data used to estimate distance between the two genes Map distance = Number of recombinant offspring Total number of offspring X 100 12.3 cM separate the s and e genes 76 + 75 542 + 537 + 76 + 75 X 100 = = 12.3 % = 12.3 m.u.
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  • Spring '08
  • SAXENA
  • Genetics, Alfred Sturtevant, recombinant offspring

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