Q2 - DNA Barcoding in Persian Gulf Fish

Theoretical 1 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Taxonomy has traditionally been based on morphology. DNA Barcoding is a new approach that aims to allow accurate and relatively simple species identification based on the nucleotide sequence of a 650-bp fragment of the mitochondrial COI gene. The Kimura-2 parameter (K2P) distance is a widely accepted index that reflects the divergence between two DNA sequences. In a study on fish inhabiting the Persian Gulf, over 150 individuals were studied that, based on morphology, represented 83 species. The average of intraspecific K2P distances based on COI sequence was calculated to be 1.15%. The average distance reported in various reputable fish studies in the world has been 0.25%-0.45%. In a study on fish inhabiting the Gulf of Mexico, again over 150 individuals were studied. Based on morphology, these fish represented 76 species, 56 genera, 32 families, 11 orders, and 2 classes. The table below presents K2P distances between specimens at different taxonomic levels.

Using the information and data, determine which of the statements are true or which are false.

A. The evolutionary rate of sequence change in a DNA fragment chosen for DNA barcoding should certainly be more rapid than the evolutionary rate of change in the H4 histone encoding gene.

B. The high average COI intraspecific K2P distance of the Persian gulf study compared to other fish studies could be explained by existence of relatively diverged clusters within one or a few of the nominal species studied (i.e. those based on morphology).

C. The data in table support the proposal that species identification of fish can be made on the basis of COI fragment sequences.

D. Table 1 suggests that COI based barcoding is not appropriate for genus identification.

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Question reproduced from IBO 2018, Theoretical Paper 1, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)