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Rest of Chapter 5

Human recombination studies Mapping by tetrad analysis in fungi Analysis of ordered tetrads Other features of recombination. Rest of Chapter 5. In humans, progeny numbers are small. Matings cannot be arranged for experiments.

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Rest of Chapter 5

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  1. Human recombination studies Mapping by tetrad analysis in fungi Analysis of ordered tetrads Other features of recombination. Rest of Chapter 5

  2. In humans, progeny numbers are small. Matings cannot be arranged for experiments. Coupling (AB/ab) vs. repulsion (Ab/aB) heterozygotes cannot be distinguished most of the time. Pedigrees can be pooled. Human pedigrees and mapping

  3. Lod scores

  4. Haploid organisms can have genetic maps made by using spore analysis. No testcrosses are needed. (review of fungal biology) Fungi in genetic studies

  5. The life cycle of the baker’s yeast (Saccharomyces cerevisiae)

  6. Types of tetrads PD = parental ditype NPD = Nonparental ditype (no linkage, PD=NPD) (with linkage, PD>NPD) TT = Tetratype tetrad

  7. Tetrad analysis of unlinked genes using unordered asci For unlinked genes, parental ditype (PD) (having 2 kinds of spores) and nonparental ditype (NPD) asci are produced in equal proportion For unlinked genes, recombination between one of the genes and its centromere produces tetratype asci (TT) having 4 kinds of spores

  8. Tetrad analysis results for linked genesin unordered tetrads-1 No crossovers or 2-strand double crossovers result in parental ditype (PD) asci. One recombination between the genes results in tetratype (TT) asci

  9. Tetrad analysis results for linked genesin unordered tetrads-2 Three-strand double crossovers give the same result as a single crossover, tetratype asci (TT). Four-strand double crossovers give non-parental ditype (NPD) asci. As a result, for linked genes, PD >> NPD.

  10. Map distance=(½)[TT]-2[NPD]+4[NPD]/total ={(½)[TT]+3[NPD]/total # of tetrads }x 100 Mapping with unordered tetrads:

  11. A branch diagram for analyzing unordered tetrads data

  12. The life cycle of an ascomycete fungus with ordered tetrads

  13. Analysis of ordered tetrad data Ordered tetrads allow one to map the distance between a gene and its centromere. No crossover between a gene and its centromere gives first division segregation. A crossover between a gene and its centromere gives a second division segregation.

  14. Recombination within genes Mitotic recombination Other types of recombination studies

  15. Fine structure mapping allows mapping the internal structure of a locus. Cistron – defines one genetic function = mutations that fail to complement The term comes from cis and trans. Lozenge gene in Drosophila:

  16. X + lzBS+ + + +lzgv X X ___________ x _______________> Y ct +lzg ct-lz=7.7 cM lz-v=5.3 cM 134 out of 16,000 progeny had normal eyes Frequency of recombination=0.008 What happened? X ct ++ + in all nonlozenge females and X + lzBSlzg v in 5 males with ‘new’ lz phenotype.

  17. Somatic recombination (mitotic crossover) can lead to twin spots

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