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

Overview Who, What, When, Where, Why Basics Example Summary Original 2002 Modified by M.Elizabeth www.marric.us/HS_4_crossing_over

Who Does Crossing-Over Effect? Eukaryotes Limited in Prokaryotes

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

Crossing Over Ref: http://gnn.tigr.org/whats_a_genome/Chp3_2.shtml Original 2002 Modified by M.Elizabeth www.marric.us/HS_4_crossing_over

When Does it Happen? Meiosis increases genetic diversity in a species 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

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

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 Original 2002 Modified by M.Elizabeth www.marric.us/HS_4_crossing_over

Homologous Chromosomes Exchanging DNA by Crossing Over From: http://www.ultranet.com/~jkimball/BiologyPages/M/Meiosis.html#crossing_over Original 2002 Modified by M.Elizabeth www.marric.us/HS_4_crossing_over

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

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

The History of Crossing Over

Linkage Gregor Mendel, 1823-1884 Carl Correns, 1900s 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 Original 2002 Modified by M.Elizabeth www.marric.us/HS_4_crossing_over http://www.oeaw.ac.at/biblio/Archiv/Mendel/mendel.html

Crossing Over Basics

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 Original 2002 Modified by M.Elizabeth www.marric.us/HS_4_crossing_over

Ref: Access Excellence http://www.accessexcellence.org/AB/GG/crossing.html Original 2002 Modified by M.Elizabeth www.marric.us/HS_4_crossing_over

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 Original 2002 Modified by M.Elizabeth www.marric.us/HS_4_crossing_over

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 Original 2002 Modified by M.Elizabeth www.marric.us/HS_4_crossing_over

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 Original 2002 Modified by M.Elizabeth www.marric.us/HS_4_crossing_over

Summary Who, What, When, Where, Why History Basics Example Summary From: http://www.ultranet.com/~jkimball/BiologyPages/M/Meiosis.html#crossing_over Original 2002 Modified by M.Elizabeth www.marric.us/HS_4_crossing_over