Two loci are considered linked if there is less than

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Unformatted text preview: and females of a species –  in male insects: no recombina*on •  use a test cross: •  AB/ab female x ab/ab male •  assump*on: no viability differences among genotypes in the F2 an example in D. melanogaster •  recombina*on rate between rosy and ebony on the X chromosome rosy homozygote wild type wild type ebony homozygotes hkp://www.sciencephoto.com/image/442308/530wm/C0118963- Ebony_body_varia*on- SPL.jpg hkp://www.biochem.arizona.edu/miesfeld/teaching/Bioc471- 2/pages/Lecture18/ Lecture18.html P genera*on ry + / ry + ♀ X + e/+ e ♂ F1 genera*on ry + / + e ♀ X ry e/ry e ♂ double mutant “tester strain” possible F2 offspring types genotypes phenotype ry +/ry e rosy eyes, wild type body color PARENTAL PARENTAL + e/ry e wild type eyes, ebony body color + +/ry e wild type eyes, wild type body color RECOMBINANT ry e/ry e rosy eyes, ebony body color RECOMBINANT data from a test cross PARENTAL RECOMBINANT genotypes phenotype number ry +/ry e rosy eyes, wild type body color 52 + e/ry e wild type eyes, ebony body color 64 + +/ry e wild type eyes, wild type body color 12 ry e/ry e rosy eyes, ebony body color 17 total 145 what is the recombina*on rate between the rosy and ebony loci? # recombinants = 17+12 = 39 total # offspring = 145 recombina*on frequency = 39/145 = 0.20 or 20% what are the units of recombina*on? •  cen*Morgans (cM) –  also called map units (m.u.) •  for small distances, d, in cM –  cM = percent recombina*on •  for larger distances, approaching the maximum between two loci (50 % recombina*on) –  map func*on is needed –  takes into account mul*ple crossovers –  with increasing distance, increasing probability of mul*ple c...
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This document was uploaded on 02/27/2014.

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