Question

directions: read and examine the passage and table below. answer the questions that follow. extensive research has been done to find similarities and differences in the dna sequences of different animals. this work is very difficult and time - consuming, but it can help biologists determine the evolutionary ancestry of a species. for example, when investigating the human genome, biologists found that about 99.5% of the dna sequences among humans are the same. considering the wide variety of traits in the human population, we are a lot similar than we are different. humans share approximately 96% of their dna sequences with chimpanzees, 85% with mice, and 75% with chickens. study the table below. organism pair, percentage of dna similarity: a - b, 97%; a - c, 85%; a - d, 50%. 1. which organism is most closely related to organism a? b, c, or d? justify your response. 2. which pair of organisms in the table is least closely related? justify your response. 3. which pair of organisms most likely shares a recent common ancestor? justify your response. 4. suppose another organism, organism x, is discovered. suggest how scientist would use dna comparison to classify organism x?

Explanation:

1. Organisms with higher DNA - similarity are more closely related. Since the DNA similarity between A and B is 97%, which is the highest among the pairs involving A, B is most closely related to A.
2. The pair with the lowest DNA - similarity is least closely related. Among the pairs, A - D has a DNA - similarity of 50%, which is the lowest, so A and D are the least closely related.
3. Organisms with higher DNA - similarity are more likely to share a recent common ancestor. A and B have 97% DNA - similarity, the highest in the table, so A and B most likely share a recent common ancestor.
4. Scientists would compare the DNA sequence of organism X with those of known organisms. The higher the percentage of DNA - similarity with a particular group of organisms, the more likely organism X belongs to that group or is closely related to it.

Answer:

1. Organism B is most closely related to organism A because the DNA - similarity between A and B is 97%, which is higher than the DNA - similarity between A and C (85%) and A and D (50%).
2. The pair A - D is least closely related as they have the lowest percentage of DNA - similarity (50%) compared to A - B (97%) and A - C (85%).
3. The pair A - B most likely shares a recent common ancestor since they have the highest percentage of DNA - similarity (97%) in the table. Higher DNA - similarity indicates a closer evolutionary relationship and a more recent common ancestor.
4. Scientists would extract and sequence the DNA of organism X. Then, they would compare its DNA sequence with the DNA sequences of known organisms. Based on the percentage of DNA - similarity, they would classify organism X. If it has a high percentage of DNA - similarity with a particular group of organisms, it would be classified as closely related to that group.