Lecture 22 exam 2

Lecture 22 exam 2 - Biology 313 Lecture 22 Oct 15, 2010...

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Biology 313 Lecture 22 Oct 15, 2010
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Chapter 7 : Linkage, Recombination and Gene Mapping 4 major topics Linkage Crossing over & recombination frequencies Gene mapping: two point testcross Gene mapping: three point testcross
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9 steps to map genes using a three point testcross (p. 181) Example is Drosophila: what is the genetic map in the region of chromosome 3 for the genes: scarlet eyes (st), recessive to red eyes (st+) ebony body color (e), recessive to gray (e+) small bristles (called spineless) (ss) recessive to normal bristles (ss+)
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STEP 1 Write out genotypes of original parents used to produce the triply heterozygous individual in the testcross; assume genes are in coupling (cis). The testcross allows the recessive and dominant alleles to be expressed in the F1!!!
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We don’t know the gene order, we are guessing here!!!!
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STEP 2 Write out the phenotypes and numbers of progeny produced; there should be 8 classes of progeny. Correlate the phenotypes with the appropriate genotypes.
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Genes are still ordered arbitrarily Data are ordered arbitrarily
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STEP 3 Rank the numbers of progeny from highest to lowest: Determine which are the Parental (NCO)* progeny: these are the two most common phenotypes Determine which are the DCO progeny: these are the two least common phenotypes * NCO = non crossover
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1 (most) 2 3 4 7 8 (least) 5 6 RANK Gene order is still arbitrary
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1 (most) 2 3 4 7 8 (least) 5 6 RANK Parental progeny DCO progeny
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This note was uploaded on 10/06/2011 for the course BIO 313 taught by Professor Rodermel during the Spring '11 term at Iowa State.

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Lecture 22 exam 2 - Biology 313 Lecture 22 Oct 15, 2010...

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