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lecture_notes_10_26_07 - Genetic Recombination and Linkage...

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Genetic Recombination and Linkage outline – Lecture 8 2007 Genetic Recombination and Linkage [Reading: SS 129-142; CR 277-281] General Recombination: Generation of new combinations of alleles Includes independent assortment Recombination is calculated by evaluation of progeny (or gamete) ratios Evaluation of recombination in diploid organisms requires assessment of alleles from both parents Analysis of recombinants generates linkage groups when genes are on the same chromosome Crossing over between homologues results in chiasmata Chiasmata are observed cytologically as an exchange between chromosomes Linkage as an exception to independent assortment Bateson and Punnett’s unexpected observations in sweet pea Each gene segregates in expected 3:1 & 1:1 ratios, but dihybrid ratio is not 9:3:3:1 Mendel’s dihybrid ratios in the F 2 (9:3:3:1) and BC 1 (1:1:1:1) generations for unlinked genes are altered if genes are linked Parental combinations of alleles are more prevalent with linkage
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