Genetic Linkage Part 3 - MappingPowerPoint PresentationSlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Genetic Linkage Part 3 - Mapping1. Mapping a three-point crossQuiz Sept. 16, 20131)Map the following three genes (A, B and C) on a chromosome.A – B = 5 muA – C = 30 muB – C = 17 mu2) How do you know which gene is in the middle if you do a 3 point cross?yellow – white recombinant frequency = 0.5%white – miniature recombinant frequency = 34.5%yellow – miniature recombinant frequency = 35.4%•Single crossovers can be used to determine the distance between two linked genes, but double crossovers (DCOs) can be used to determine the order of three genes on the chromosome•The expected frequency of double-crossover gametes is much lower than that of either single-crossover gamete class•To study double exchanges, three pairs of genes must be investigated, each heterozygous for two alleles•In three-point mapping, the parent must be heterozygous for all three genes under consideration•As in two-point mapping, the definitive experiment is a test cross with a homozygous recessive. •The noncrossover test cross phenotypes occur in the greatest proportion of offspring•The double-crossover phenotypes occur in the smallest proportion•The distance between two genes in a three-point cross is equal to the percentage of all detectable exchanges occurring between them and includes all single and double crossoversFigure 5.8© 2012 Pearson Education, Inc.Figure 5.10Figure 5.11© 2012 Pearson Education, Inc.Figure 5.13Problem 14 from the end of chapter 5 problems:In Drosophila, a cross was made between females – all expressing the three X-linked recessive traits scute brisltes (sc), sable body (s), and vermilion eyes (v) – and wild-type males. In the F1, all females were wild-type, while the males expressed all three mutant traits. The cross was carried to the F2 generation (and remember, this is a test cross, since the males are recessive), and 1000 offspring were counted, with the results shown below.Phenotypes offspringsc s v 314+ + + 280+ s v 150sc + + 156sc + v 46+ s + 30sc s + 10+ + v 14a) Using proper nomenclature, determine the genotypes of the P1 and F1 parents.b) Determine the sequence of the three genes and the map distances between them.Exam Question:In 1923, Bridges and Morgan reported the following data from Drosophila that were collected after a test cross involving an F1 fly heterozygous for three recessive mutant phenotypes; claret (ca), ebony (e), and rough (ro). Wild type 49Ebony 1Claret 395Rough 119Ebony, rough 370Ebony, claret 89Rough, claret 1Ebony, rough, claret 66 Use Chi Square analysis to test the hypothesis that the ebony gene obeys Mendel’s Law of Random Segregation.Construct a genetic map of these three loci showing the distances between loci in map units.Exam Question:Three recessive traits in maize plants are as follows: yellow seedlings are recessive to green seedlings, clear kernels are recessive to colored kernels, bronze plant color is recessive to normal color. A normal colored plant with green seedlings and clear kernels was crossed with a bronze plant with yellow seedlings and colored kernels. The F1 plants were then crossed with a plant homozygous mutant for all three loci and the following results were obtained: 1,138 normal, green seedlings, clear kernels 72 bronze, green seedlings, clear kernels 295 bronze, green seedlings, colored kernels 1,127 bronze, yellow seedlings, colored kernels 67 normal, yellow seedlings, colored kernels 289 normal, yellow seedlings, clear kernels 7 normal, green seedlings, colored kernels 5 bronze, yellow seedlings, clear kernels Use Chi Square analysis to test the hypothesis that the seedling and kernel color genes obeys Mendel’s Law of Independent Assortment.The seedling color gene is located at position 7 on Chromosome 9 of the corn genome. Use this information to draw a map indicating where all three genes are located on Chromosome