Homework2-KEY

Homework2-KEY - H omework #2 K EY I ncluding examples of...

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Homework #2 KEY Including examples of answers that worked from the class (many good ones were submitted, so this is just a small subset of them) ECL242_PHR242 Due Jan 13, 2010 Also not required for homework – just as guides for your reading and preparation for midterm For Ch3 P(ID) Question 4 on page 100 see Answer key excel file “CH3Q4-PID.xls” For homework to hand in, pick any two of the following 4 questions to hand in for homework. You may use the other questions as study questions for yourself. 1. Explain Probability of Identity PID in your own words (chapter 3). The probability of identity is a calculation to estimate the chance that any two individuals in a population have the same genotype (genetic profile over multiple loci). This calculation is a measure of confidence that two samples from a population can be correctly identified as individuals. Information about the population understudy, such as allele frequencies, relatedness and inbreeding should be known to calculate an accurate P ID. The equation by Paetkau and Strobeck (1994) assumes random mating and no inbreeding, situations which may not always be realistic. Waits, Luikart and Taberlet (2001) examined the accuracy of P ID calculations by examining observed and expected values, finding the observed values to be consistently low. They have developed a P ID calculation for siblings with consideration of multilocus genotypes between individuals. Waits L P; Luikart G; Taberlet P. 2001. Estimating the probability of identity among genotypes in natural populations: cautions and guidelines. Molecular ecology 2001;10(1):249-56. The Probability of Identity (P ID ) is the chance that two individuals in a population share the same genetic profile (of the loci that are evaluated). It can be used when the source of the
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DNA sample is unknown, usually as a result of non-invasive DNA sampling. Because many alleles can be shared within a population, it can be difficult to deduce if two DNA samples came from the same individual or not so we use P ID to calculate the probability that the samples share the same alleles. If the P ID is less than 0.05 (or whatever threshold is appropriate for specific question) for a randomly mating population than we can assume the two DNA samples came from different individuals. This probability will be low, and the ability to distinguish individuals will be low, if the available marker is not very polymorphic and therefore many individuals share the same genotype. The use of a highly polymorphic marker, a marker with rare alleles, or a combination of several markers increases the probability of positive identification. To calculate P ID we first need to determine the frequency of each allele at each marker locus in the population. 2.
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Homework2-KEY - H omework #2 K EY I ncluding examples of...

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