crossing over genetic recombination jack cassidy, jessica matthews, keith murphy, mike nickelsburg
TRANSCRIPT
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Crossing OverCrossing OverGenetic RecombinationGenetic Recombination
http://library.thinkquest.org/19037/genome3.html
Jack Cassidy, Jessica Matthews, Keith Murphy, Mike Nickelsburg
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Original 2002Modified by M.Elizabethwww.marric.us/HS_4_crossing_over
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Overview
• Who, What, When, Where, Why• Basics• Example• Summary
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Who Does Crossing-Over Effect?
EukaryotesLimited in Prokaryotes
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What is Crossing Over?
The exchange of chromosomal segments between two non- sister
chromatids
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5Ref: http://gnn.tigr.org/whats_a_genome/Chp3_2.shtml
Crossing Over
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When Does it Happen?
During Prophase I of MeiosisRemember the differences between
Mitosis and Meiosis?
Meiosis increases genetic diversity in a speciesMitosis creates genetically identical daughter cells
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Where does Crossing Over Occur?
Genetic swapping occurs between paired homologous chromosomes in our sex cells
—The Egg and Sperm
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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
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Homologous Chromosomes Exchanging DNA by Crossing Over
From: http://www.ultranet.com/~jkimball/BiologyPages/M/Meiosis.html#crossing_over
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Why Does Crossing Over Occur?
To provide genetic variation during meiosis
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Its Why You and I Don’t Look Alike
Crossing Over ensures a combination of the maternal
and paternal genes we inherited
BOTTOM LINE
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The History of Crossing Over
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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://www.oeaw.ac.at/biblio/Archiv/Mendel/mendel.html
http://www.library.villanova.edu/html2/blueprints/feb01index.html
http://zygote.swarthmore.edu/cleave1.html
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Crossing Over Basics
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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
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Ref: Access Excellencehttp://www.accessexcellence.org/AB/GG/crossing.html
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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
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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
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Genes get shuffled when chromosomes exchange pieces
Watch an animation of crossing over with an explanationof how the concept was discovered at
http://www.dnaftb.org/dnaftb/11/concept/index.html
This web site was produced by theDolan DNA Learning Center, Cold Spring Harbor Laboratory
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Summary
• Who, What, When, Where, Why• History• Basics• Example• Summary
From: http://www.ultranet.com/~jkimball/BiologyPages/M/Meiosis.html#crossing_over