BIOL 1107 1nd Edition Lecture 31 Outline of Last Lecture I Sex Chromosomes II Human Inheritance III Pedigree Outline of Current Lecture I II Crossing Over Prophase I Genetic Recombination and Mapping Genes Current Lecture I Crossing Over Prophase I Genes on the same chromosome inherited together Crossing over occurs at prophase I and allows shuffling of genes to take place Metaphase I homologous chromosomes lining up on metaphase plate Anaphase II sister chromatids separate Crossing over the exchange of corresponding segments of DNA molecules by nonsister chromatids o in effect end portions of two nonsister chromatids trade places each time a crossover occurs o it is completed while homologs are in synapsis held tightly together by proteins along their lengths o Synapsis ends in mid prophase and the chromosomes in each pair move apart slightly 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 II Predicted ratios o If genes were located on different chromosome 1 1 1 1 o If genes are located on the same chromosome and parental alleles are always inherited together 1 1 0 0 no crossing over occurs Genetic Recombination and Mapping Genes TH Morgan s Fly Experiment see image above recall that most of the offspring from the test cross for body color and wing size had parental phenotypes That suggested that the two genes were on the same chromosome since the occurrence of parental types with a frequency greater than 50 indicates that the genes are linked About 17 of the offspring however were recombinants Faced with these results Morgan proposed that some process must occasionally break the connection between specific alleles of genes on the same chromosome Subsequent experiments demonstrated that this process now called crossing over accounts for recombination of linked genes Recombinant chromosomes resulting from crossing over may bring alleles together in new combinations and the subsequent events of meiosis distribute the recombinant chromosomes to gametes Spotting Recombination check elc New for question o Which of the following are parental 2 ABc black long four no recombination of it occurred
View Full Document
Unlocking...