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

2. 21 Apr 20022 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. 21 Apr 20025 Ref: http://gnn.tigr.org/whats_a_genome/Chp3_2.shtml Crossing Over

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. 21 Apr 20028 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. 21 Apr 20029 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. Its Why You and I Don’t Look Alike Crossing Over ensures a combination of the maternal and paternal genes we inherited BOTTOM LINE

12. The History of Crossing Over

13. 21 Apr 200213 Linkage Gregor Mendel, 1823-1884 –Patterns of Inheritance Carl Correns, 1900s –Gene Linkage Alfred Sturtevant http://www.oeaw.ac.at/biblio/Archiv/Mendel/mendel.html http://www.library.villanova.edu/html2/blueprints/feb01index.html http://zygote.swarthmore.edu/cleave1.html

14. Crossing Over Basics

15. 21 Apr 200215 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. 21 Apr 200216 Ref: Access Excellence http://www.accessexcellence.org/AB/GG/crossing.html

17. 21 Apr 200217 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. 21 Apr 200218 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. 21 Apr 200219 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. 21 Apr 200220 Summary Who, What, When, Where, Why History Basics Example Summary From: http://www.ultranet.com/~jkimball/BiologyPages/M/Meiosis.html#crossing_over