CSI Wildlife | Case Two | Building a Reference Map: Review

Building a Reference Map

Let's Review:

A researcher collected DNA from five dung samples in an elephant population. She amplified the sequence corresponding to the STR locus called "Marker X" and determined each allele's size using gel electrophoresis. The data are shown in the table. Samples that have an identical fragment for both alleles are homozygous for Marker X. If the alleles are different, the individual is heterozygous.

Dung Sample	Allele 1	Allele 2
1	237 bp	237 bp
2	252 bp	245 bp
3	255 bp	252 bp
4	252 bp	252 bp
5	245 bp	237 bp

Which of the lanes shown at left below (scroll down to view) corresponds to the Marker X profile for this population?

A. Lane A
B. Lane B
C. Lane C
D. Lane D

Try again. Look at the allele sizes in the table and look for a lane that has all of them.

Correct. Lane C has bands corresponding to allele sizes 237 bp, 245 bp, 252 bp, and 255 bp, which are all the alleles in the table.

Based on these five samples, which allele has the highest frequency in this population?

A. 237 bp
B. 252 bp
C. 255 bp
D. 245 bp

Try again. The allele with the highest frequency is the most common allele in the table.

Correct. The 252-bp allele is the most common in the population. Its frequency is 4/10 = 0.4 or 40%.