04BIS10110152013RecombinLect4

Assortment 2 2 0 e e 0 observed progeny types e

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Unformatted text preview: or linkage (p.48-50) Chi-square ­ When the RF values of recombinant progeny (i.e., those not When exhibiting the parental phenotypes) approach 50%, it is difficult to distinguish between independent assortment (interchromosomal recombination) and intrachromosomal recombination between two “linked” loci. This can be seen from the test cross data for the following three loci. from AB ab x ab ab Phenotypes 1159 1017 17 12 12 2205 BC bc x bc bc Phenotypes AB 770 ab 716 Ab 401 nonparentals aB 318 aB 2205 BC bc Bc Linked or Linked bC Unlinked? Unlinked? BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 48 Chi-square test for linkage Chi-square ­ The likelihood of linkage can be tested using the The Chi-square test (page 127). The test begins by Chi-square making a hypothesis. For example: making q “ The B, C loci are unlinked and located on the separate chromosomes.” chromosomes.” ­ Next, the Chi-square formula is used to compare the Next, observed number of progeny types to the expected number of progeny types, assuming independent assortment (1:1:1:1). assortment 2 χ= 2 Σ (0 - E) E 0 = observed progeny types E = expected progeny types based on the hypothesis Σ = sum of calculations for each progeny types sum BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 49 Chi-square test for linkage Chi-square ­ Calculating χ2 Calculating for all 4 progeny types, assuming independent assortment or a 1:1:1:1 ratio. With 2205 total progeny, independent assortment would produce an expected ratio of: 551 : 551 : 551 : 551 (2205÷4) (2205÷4) χ2 = ( 0 - E 1 )2 (0 - E2)2 (0 - E 3 )2 (0 - E 4 )2 + + + E1 E2 E3 E4 BC bc Bc bC (770 - 551)2 (716 - 551)2 (401 - 551)2 (318 - 551)2 551 551 551 551 2 + + + χ= 551 551 551 551 χ2 = 87.0 + 49.4 + 40.8 + 98.5 = 276.5 BIS101­001, Spring 2013—Genes and...
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