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 “CH3Q4PID.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):24956.
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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View Full DocumentDNA sample is unknown, usually as a result of noninvasive 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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 Winter '08
 Scholey
 High mutation rate, DNA Samples, adult feathers, Luikart G

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