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

21 Apr Overview Who, What, When, Where, Why Basics Example Summary

Who Does Crossing-Over Effect? Eukaryotes Limited in Prokaryotes

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

21 Apr Ref: Crossing Over

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

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

21 Apr 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

21 Apr Homologous Chromosomes Exchanging DNA by Crossing Over From:

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

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

The History of Crossing Over

21 Apr Linkage Gregor Mendel, –Patterns of Inheritance Carl Correns, 1900s –Gene Linkage Alfred Sturtevant

Crossing Over Basics

21 Apr Crossing Over Basics Occurs at One or More Points Along Adjacent Homologues during Synapsis Points contact each other DNA is Exchanged

21 Apr Ref: Access Excellence

21 Apr 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

21 Apr 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

21 Apr 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

21 Apr Summary Who, What, When, Where, Why History Basics Example Summary From: