Sec4-linkage+what+csome - Independent assortment and...

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Independent assortment and assignment of linkage 1 J.L.Marsh Bio 137B What chromosome is it on?? How to establish Linkage? 2b. What is Mendels 2nd law? Independent assortment Genes on different chromosomes will segregate equally BUT independently AAbb x aaBB --> AaBb x AaBb --> 9:3:3:1 A_B_: A_bb:aaB_:aabb SO WHAT? ? = First step in mapping is to establish linkage to a particular chromsome To do that, we make use of the Principle of independent assortment. It says, alleles of genes ON SEPARATE CHROMOSOMES segregate independently of one another. Today, thinking of chromosomes, we can think of this as the two homologs of different chromosomes assorting randomly or independently. We establish linkage by eliminating different chromosomes as the possible location of a gene. Namely, if our gene of interest assorts independently from alleles of a 'marker' gene already known to be on a given chromosome, that chromosome is eliminated as the site of linkage (with the one proviso that if the chromosome is large and your markers sparse, loci that are far away from each other can assort independently due to recombination). If our gene of interest shows lack of independence from a particular chromosome marker, then that chromosome,is a candidate for the location of the gene. A TYPICAL RESPONSE to the question of how would you find the gene that was mutated in a person with a birth defect is ,”I would sequence their DNA and find the mutated site”. That is like saying there is a house in the USA with a number missing from their address on the door and you saying we will find it by looking at all the 100million houses. More practical is to locate the state (chromosome), whether in Northern CA or SoCal (the chromosome arm) etc. Mendel’s second law can be used to locate a gene locus on a chromosome. MENDELS SECOND LAW & THE RELATIONSHIP BETWEEN INDEPENDENT ASSORTMENT AND LINKAGE GROUPS OBJECTIVES Step 2 in isolating a gene or developing a diagnostic is to determine what chromosome its on.
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This note was uploaded on 10/27/2009 for the course BIO SCI 05580 taught by Professor Marsh during the Fall '09 term at UC Irvine.

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Sec4-linkage+what+csome - Independent assortment and...

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