(1) An interrupted mating procedure was employed to map the following genes: car
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(1) An interrupted mating procedure was employed to map the following genes: carA, cysE, hisB, ivIA, leuC, pabB and serD. An Hfr strain wild-type for each of these genes was mated to an F- strain mutant for all with the following results Minutes that bacterial cells were alowed to mate before conjugation was halted Percent of surviving colonies with the following genotypes carA +hisB MAleuC pabB serD 1002 75 100 26 00 52 55 100 54 55 100 0 100 0 100 0 100 0 100 0 17 100 0 100 0 25 100 0 83 100 24 84 80 100 57 25 100 100 57 (a) The procedure requires the use of at least one more gene to be feasible, what kind of gene is this and what should you know about its location? (b) What is the order of genes on the chromosome and the approximate map distance in minutes they are (c) It is impossible to accurately map some of the genes. Which ones, why, and how could you go about mapping them more accurately?Explanation / Answer
A genetic map used to locate a gene or group of genes and their relative distances.
The chromosome consists of the number of genes, located adjacent to each other along with noncoding regions among them. The gene order is nothing but the sequential order of the locus of genes present on a chromosome. The gene order describes relatively, which genes are away from each other or which genes are adjacent, which comes first, which comes in the middle and which comes away from others etc.
Map distance: It is a measure of relative distance between two genes. It describes whether genes are linked or independent. it depends upon the number of recombinants in an offspring. If the distance between two genes is 1 map unit it indicates that the percentage of recombinants(crossing over products) is one.
c) Genetic maps are not universally accurate for all genes, for complex Mendelian traits it is impossible to plot an accurate genetic map. The errors may be resulted because of genotyping errors or from the use of a limited number of informative meioses to generate maps. the problems in identifying the recombinants, assembling them in order and errors in measuring distances may lead to inaccurate maps. The accuracy of the map can be improved by expanding the experiment size and applying statistical methods to analyse the data. For example, higher genetic map accuracy is possible by creating maps using the method in which a likelihood-ratio criterion of ?3, as opposed to using a minimum-recombination map.
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