CSI Wildlife: Using Genetics to Hunt Elephant Poachers

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Student Worksheet 2

b. Use the formulas below to calculate the probability of another individual having the same genotype for

each individual locus. Enter the formulas and probability in Table 4.

• If the ivory sample is homozygous for an STR locus, the probability (P

(genotype for locus X)

) that another

individual has the same genotype for the STR locus is:

P

(genotype for locus X)

= (frequency of Allele 1)

2

• If the ivory sample is heterozygous for an STR locus, the probability (P

(genotype for locus X)

) that another

individual has the same genotype for the STR locus is:

P

(genotype for locus X)

= 2 × (frequency of Allele 1) × (frequency of Allele 2)

values for the probability

(0.60)

2

Calculated probability for

the locus

0.36

Table 4. The probability that another elephant in the same population has the same genotype at each individual STR locus,

based on the allele frequencies in Table 3.

c. To determine the probability that another individual has the same genotype for each of the five STR loci

(in other words, the same genetic fingerprint), multiply all the individual probabilities together. What is

the probability that all five match? __________

7. Impressed with your work, your boss now asks you to apply what you have learned to the genotype for the

ivory sample for all 16 STR loci, listed in Table 5 below. The first five STR loci are the same as the ones listed

in Table 4. In addition, your colleague has been able to collect additional samples of elephants from the

same population as the ones shown in Table 2. He now has allele frequency data based on 80 alleles, shown

in the table below.

Table 5. Allele size and frequency for 16 STR loci from a sample of 40 elephants (80 alleles).

a. Compare the frequency of the alleles for STR loci FH19, FH60, FH67, FH71, and FH129 that you

completed in Table 3 with the values in Table 5. Why do you think the values differ?

b. Calculate the probability that another individual has the same genotype at all 16 STR loci by using the

same procedure as Questions 6b and 6c. What is the probability of an identical match with another

elephant at all 16 STRs? __________________