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Chapter 4a-4.docx

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BIOL 2000
Joseph Rasmussen

Chapter 4a-4 Clicker question  Genes for curly wings (cy) and ebony eye color (e) are 20 m.u apart. Two trans-dihybrid individuals are mated to produce F2 progeny. What will the frequency of individuals homozygous recessive for both genes in the F2?  cy= curly cy+= wild type  e = ebony e+= wild type  cy+ / e + X cy+ / e+  To get recessive homozygous for both we need a recombination.  Frequency for F1 recombination is 20% (two kinds)  To get one recombination is 10%  F2 is 10% multiplied by 10% =1% Why did we calculate the map distance of 8.6 cM?  By comparing the parental cases to the DCO classes, we can recognize the gene in the middle, because its alleles switch places relative to the outer two genes in the DCO class o Crossed twice between CER3 and LFY and YI Rules for a three-point test cross:  There should be 8 phenotypic classes o Two cubed combinations  Progeny classes are grouped in pairs = reciprocal cross over events o Represent the two halves of the cross over events o Don’t group by numbers, but by cross over events  LFY CER3 yi pairs with lfy cer3 YI  Largest classes are the parental  Smallest classes are the double cross-over classes (DCO) Recombinant frequency between outer genes  = sum of frequency between outer genes  = (sum of SingleCrossOver classes) + 2(sum of DoubleCrossOver classes)/total o = (26+32+11+17) + 2(1+1) o = 0.9 o =map distance = 9cM  450 lfy CER3 YI are in trans( lfy to CER3/YI) and cis (CER3 and YI)  462 LFY cer3 yi are in trans (LFY to cer3/yi) and cis (cer3 and YI) o DCO = 1 lfy cer3 yi all in cis o DCO= 1 LFY CER3 YI all in cis  LFY/l
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