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The doctoral student has gathered all the data together and is defending his findings at a gathering of scientists. He begins his concluding remarks with this statement: “My belief concerning the coughing frog is that it should be…”

Which statement is the one he most likely made?

The Coughing Frog

Use the passage below, as well as the original reading, to answer this question.

Scientists use a number of pieces of evidence to determine if an organism should be classified as its own species. These pieces of evidence almost always include making comparisons between the new organism and other species who are similar to the new organism. One such comparison can be made by looking at DNA sequences between organisms, scientists can not only determine species origin, but they can also determine how closely related species are and gather knowledge about an organisms evolutionary history.

The doctoral student has drawn blood samples from each of five organisms: The coughing frog, a Northern Leopard Frog, a Southern Leopard Frog, the American Bullfrog, and a chicken. Using the latest in automated techniques, he sequenced DNA from an area in the first chromosome from each organism. Using a sophisticated database, he was able to compare the sequences of each of the species to the others. The goal of the comparison was to show the per cent homology (likeness) between the sequences. The results of the comparison are shown in the chart below:

Per Cent Homology between DNA Sequences Taken From Chromosome #1 Blood Samples

Organism Coughing Frog NOrthern Leopard Frog Southern Leopard Frog Bullfrog Chicken
Coughing Frog 100 92 88 70 14
Northern Leopard Frog 92 100 93 74 16
Southern Leopard Frog 88 93 100 72 18
Bullfrog 70 74 72 100 21
Chicken 14 16 18 21 100

“classified as a member of the Northern Leopard frog species, based on the fact they share a high percentage of DNA homology and identical VB gene sequences.”


“classified as a member of the Southern Leopard Frog species, based on the fact they share a high percentage of DNA homology and identical PC gene sequences.”


“classified as a new species, as the DNA homology and gene sequence evidence show that it is its own unique organism.”


“classified as a unique species, as it is more closely related to a bullfrog than either type of leopard frog, based on the DNA homology sequence comparisons.”

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