BIOL 1411 1st Edition Lecture 18 Outline of Last Lecture I Dominance a Incomplete dominance b Co dominance II Epistasis Outline of Current Lecture I Genetic Linkage Lecture What is the relationship between genes and chromosomes o Experiments of Thomas Hunt Morgan o Established the fly as a model for genetic studies Confirmed Mendel s principles of dominance segregation and independent assortment later supported chromosome theory of inheritance o However his studies demonstrated some experiments on two or more loci in the fly exhibited patterns inconsistent with the law of independent assortment o Alleles of separate loci were transmitted together to offspring a phenomenon called linkage Some alleles do not assort independently o Test cross heterozygotes at clack locus b b and vestigial locus vg vg crossed with homozygous recessive bb vgvg o 2300 flies scored too many parental types and too few recombinant types observed What is the relationship between genes and chromosomes o Frequency of crossing over between two linked genes is proportional to the distance between them Frequencies of recombinant gametes and resulting non parental offspring are greater for loci that are farther apart Recombinant frequency of recombinant offspring divided by total of offspring recomb total Maximal recombinant frequency is 5 also the expectation under independent assortment These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Absolute Linkage is rare even alleles of different loci that are very close on the same chromosome are sometimes recombined by crossing over male drosophila being the execption What is the relationship between genes and chromosomes o All of the loci on a chromosome form a linkage group o Recombinant frequencies can be used to make genetic maps showing the arrangement of genes along a chromosome o Distance between genes map unit 100 x recombinant frequency o Map Unit also called a centimorgan cM
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