Lecture 15 - Crossing-over Meiotic crossing-over : breaking...

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Lecture 15: (more) Linkage Crossing over in meiosis what really happens Key words: Key Figures: Recombination 17.5 Cross-over Holliday Junction Double strand break repair model Spo11 (an endonuclease) Practice problem ; None
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y+ w+ m+ Last lecture: Recombination frequency reflects how far apart genes are on the chromosome. Close together :will be inherited together ->more parental types -> recombinant types 1% Far apart : ‘linkage’ tends to break ->fewer parental types than above ->more recombinant types 33% Why?
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Recombination : -The process by which offspring derive a combination of genes different from that of either parent. -The generation of new allelic combination. -In higher organisms, this can occur by crossing-over .
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y+ w+ m+ y w m Normally , the order of genes along the chromosome is the same on homologs X chromosomes in fly
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w+ m+ w m Parental types: w+ m+ w m w+ m w m+ Recombinant types: w+ m w m+ Meiotic
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Unformatted text preview: Crossing-over Meiotic crossing-over : breaking and rejoining of maternal and paternal chromosomes (homologs) that results in the exchange of corresponding sections. Review prophase of meiosis I Remember - Crossing-over in Meiosis I Cross-over here - During pairing of homologs y+ w+ m y w m+ y+ w+ m y w m+ y+ w+ m y w m+ Cross-over anywhere Why? Any Cross-over event here will recombine y+ and m Genes far apart can recombine from many cross over events. Closer genes recombine only if cross-over happens to be between them y+ w+ m+ y w m Must cross-over here to recombine w+ and y Can use recombination frequency between gene pairs to find their arrangement on chromosomes; mapping (next lecture) The current model of meiotic recombinatio n The Double stranded break repair model The structure of a Holliday Junction...
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Lecture 15 - Crossing-over Meiotic crossing-over : breaking...

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