1. Genetic Recombination
Jack Cassidy, Jessica Matthews, Keith Murphy, Mike Nickelsburg
Crossing Over
Genetic Recombination

2. Overview Who, What, When, Where, Why Basics Example Summary
Original 2002
Modified by M.Elizabeth

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
Original 2002
Modified by M.Elizabeth

6. 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

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
Original 2002
Modified by M.Elizabeth

9. Homologous Chromosomes Exchanging DNA
by Crossing Over
From:
Original 2002
Modified by M.Elizabeth

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

11. 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

12. The History of Crossing Over

13. Linkage Gregor Mendel, 1823-1884 Carl Correns, 1900s
Patterns of Inheritance
Carl Correns, 1900s
Botonist – cites Mendel and Darwin: cytoplamic inheritance
Alfred Sturtevant, Family horse farm and pedigree study: found traits that travel together = linkage
Original 2002
Modified by M.Elizabeth

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
Original 2002
Modified by M.Elizabeth

16. Ref: Access Excellence
Original 2002
Modified by M.Elizabeth

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
Original 2002
Modified by M.Elizabeth

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
Original 2002
Modified by M.Elizabeth

19. Genes get shuffled when chromosomes exchange pieces
Watch an animation of crossing over with an explanation
of how the concept was discovered at
This web site was produced by the
Dolan DNA Learning Center, Cold Spring Harbor Laboratory
Original 2002
Modified by M.Elizabeth

20. Summary Who, What, When, Where, Why History Basics Example Summary
From:
Original 2002
Modified by M.Elizabeth