BIOL 234 - L6 (post) - Crossing over and linkage Lecture 6...

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Crossing over and linkage Lecture 6 BIOL 234 May 29, 2017
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Learning objectives Use diagrams of meiotic crossing over to understand the consequences of crossing over From analysis of data from a cross, identify scenarios involving linkage Determine the allelic configuration of the individuals in the cross and explain how recombinant configurations were created Calculate the map distance between linked genes Given map distance, predict frequency of parental/recombinant gametes and progeny genotypes BIOL 234 summer 2017 L6 2
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Genotypic ratios and linkage Segregation: 3:1 or 1:2:1 ratio: single nuclear gene, two alleles 9:3:3:1 ratio: two genes, two alleles each, independent assortment Modifications to the 9:3:3:1 ratio are seen with: Linkage Genetic interactions BIOL 234 summer 2017 L6 3
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Crossing over A process of recombination between homologous chromosomes Occurs during prophase I of meiosis Can result in exchange of alleles between non-sister chromatids What does crossing over facilitate? What is required for crossing over? Introduction to Genetic Analysis, 10 th edition BIOL 234 summer 2017 L6 4
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Meiosis 5 Base pairing helps to join homologous pairs of chromosomes BIOL 234 summer 2017 L6
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Meiosis 6 Base pairing helps to join homologous pairs of chromosomes DNA sequences that bind must be complementary Ensures that homologous chromosomes pair BIOL 234 summer 2017 L6 A C G T T G A A C T G T G C A A C T T G A C
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Meiosis 7 Homologous chromosomes are: Correctly paired for metaphase I Aligned for crossing over BIOL 234 summer 2017 L6
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Crossing over oca2 B T/A = brown hair oca2 bl G/C = blonde hair herc2 B C/G = brown eyes herc2 g A/T = green eyes oca2 B herc2 B oca2 bl herc2 g BIOL 234 summer 2017 L6 8
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Crossing over oca2 B herc2 B herc2 g oca2 bl oca2 bl oca2 B herc2 B herc2 g BIOL 234 summer 2017 L6 9
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