BIOL 1411 1st Edition Lecture 18Outline of Last Lecture I. Dominancea. Incomplete dominanceb. Co-dominanceII. EpistasisOutline of Current Lecture I. Genetic LinkageLecture- What is the relationship between genes and chromosomes?o Experiments of Thomas Hunt Morgano Established the fly as a model for genetic studies. Confirmed Mendel’s principles of dominance, segregation, and independent assortment; later supported chromosome theory of inheritanceo However, his studies demonstrated some experiments on two or more loci in the fly exhibited patterns inconsistent with the law of independent assortmento Alleles of separate loci were transmitted together to offspring, a phenomenon called linkage- Some alleles do not assort independentlyo 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 groupo Recombinant frequencies can be used to make genetic maps showing the arrangement of genes along a chromosomeo Distance between genes = map unit= 100 x recombinant frequencyo Map Unit also called a centimorgan
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