ch13 part 3 - CH 13: Mendel and the gene Last Thursday. 1....

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CH 13: Mendel and the gene 1. Predicting genotypes and phenotypes 2. Mendel’s contributions to genetics 3. Chromosomal theory of inheritance 4. Testing and extending the chromosome theory Last Thursday… Today… 1. Sex linkage & gene linkage 2. Extending Mendel’s rules (+ complexity) 3. Application of Mendel’s rules to humans
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Sex-linkage = genes are carried on the sex chromosomes (females and males w/ different # alleles) Sex Linkage and Gene Linkage Linkage = The physical association of genes on the same chromosome Do these assort independently? Genes that are linked together don’t assort independently unless genetic recombination . Still lower proportion
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Mapping gene loci= linkage maps
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Linkage and Genetic Mapping Genes on a chromosome are arranged in a linear array Distance between genes dictates the frequency of crossing over ( greater distance on the chromosome = >) A genetic map is a map of the relative locations of specific genes on a certain chromosome Figure 9.26 Chromosome g l 17% 9% 9.5% recombination frequencies = % of recombinant offspring among total offspring – represent relative distances between pairs of genes c
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Genes > 50 map units apart assort independently
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? ? ? Which gene (colored band) corresponds to: Ruby eyes: orange band (7.3+6.2) Crossveinless wings: blue band Miniwings: white band HINT: Use the singed bristles row in the table.
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So far: Discrete traits: 2 clear-cut variants Complete dominance/ recessiveness Only 2 alleles per gene Only 1 character controlled by each gene Each character controlled by only 1 gene Review: patterns of inheritance But…we know that there are more complicated patterns of inheritance! Sex-linkage Linkage
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Quantitative variation = differences in degree of variation (not discrete!) (hair color, height, weight) Incomplete dominance Codominance Multiple allelism Polymorphism Pleiotropy Epistasis
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ch13 part 3 - CH 13: Mendel and the gene Last Thursday. 1....

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