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Crossing Over

Crossing Over

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Crossing Over

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  1. Jack Cassidy, Jessica Matthews, Keith Murphy, Mike Nickelsburg Crossing Over Genetic Recombination http://library.thinkquest.org/19037/genome3.html

  2. Overview • Who, What, When, Where, Why • Basics • Example • Summary

  3. Who Does Crossing-Over Effect? Eukaryotes Limited in Prokaryotes

  4. What is Crossing Over? The exchange of chromosomal segments between two non- sister chromatids

  5. Crossing Over Ref: http://gnn.tigr.org/whats_a_genome/Chp3_2.shtml

  6. When Does it Happen? During Prophase I of Meiosis Remember the differences between Mitosis and Meiosis? Meiosis increases genetic diversity in a species Mitosis creates genetically identical daughter cells

  7. Where does Crossing Over Occur? Genetic swapping occurs between paired homologous chromosomes in our sex cells—The Egg and Sperm

  8. Egg and Sperm • Chromosomes pair • Chromosomes may swap genetic material • New genetic material has been acquired from the other homologue • NOTE: Genes that have a tendency to remain together during crossing over are said to be linked—we will talk about this concept during Crossing Over Basics

  9. Homologous Chromosomes Exchanging DNA by Crossing Over From: http://www.ultranet.com/~jkimball/BiologyPages/M/Meiosis.html#crossing_over

  10. Why Does Crossing Over Occur? To provide genetic variation during meiosis

  11. BOTTOM LINE Its Why You and I Don’t Look Alike Crossing Over ensures a combination of the maternal and paternal genes we inherited

  12. The History of Crossing Over

  13. Linkage • Gregor Mendel, 1823-1884 • Patterns of Inheritance • Carl Correns, 1900s • Botonist – cites Mendel and Darwin: cytoplamic inheritance • Alfred Sturtevant, 1891-1970. Family horse farm and pedigree study: found traits that travel together = linkage http://zygote.swarthmore.edu/cleave1.html http://www.library.villanova.edu/html2/blueprints/feb01index.html http://www.oeaw.ac.at/biblio/Archiv/Mendel/mendel.html

  14. Crossing Over Basics

  15. Crossing Over Basics • Occurs at One or More Points Along Adjacent Homologues during Synapsis • Points contact each other • DNA is Exchanged http://waynesword.palomar.edu/images/cross3.jpg

  16. Ref: Access Excellence http://www.accessexcellence.org/AB/GG/crossing.html

  17. Crossing Over Basics • Gene Mapping • Tracking crossing over helps determine where genes are located on the chromosome • Genes that are far apart have a GREATER chance of crossing over • Genes that are closer have a LESS LIKELY chance of crossing over • Genes that stay together are said to be LINKED • One gene can be identified as a MARKER that can infer the presence of the other gene • This can be used in identifying disease predisposition

  18. Crossing Over Basics • Gene Mapping • Tracking crossing over helps determine where genes are located on the chromosome • Genes that are far apart have a GREATER chance of crossing over • Genes that are closer have a LESS LIKELY chance of crossing over

  19. Genes get shuffled when chromosomes exchange pieces Watch an animation of crossing over with an explanation of how the concept was discovered at http://www.dnaftb.org/dnaftb/11/concept/index.html This web site was produced by the Dolan DNA Learning Center, Cold Spring Harbor Laboratory

  20. Summary • Who, What, When, Where, Why • History • Basics • Example • Summary From: http://www.ultranet.com/~jkimball/BiologyPages/M/Meiosis.html#crossing_over