A study published in 2000 sequenced part of the mitochondrial cytochrome b gene from 61 brown bears from two sites in Alaska. On
e population of brown bears lives on the coastal mainland of Alaska, while a separate population lives on the ABC islands in southeastern Alaska. Mainland and ABC brown bears differ by 11 fixed nucleotide substitutions in the cytochrome b gene. This suggests that the two brown bear populations represent genetically unique clades. The researchers compared the cytochrome b sequences of the two clades of Alaskan brown bears to those of 55 polar bears. The analysis showed that polar bears and ABC brown bears differ at only three nucleotides in this gene, whereas polar bears and mainland brown bears had more differences. Based on the results of the 2000 study, how should the portion of the tree extending from branch point 7 be altered.
The mainland brow bear and the ABC brown bear, both share common ancestor 7. but, the polar bear also descended from ancestral specie 7. because not all descendant of ancestral specie 7 are included, that group is considered paraphyletic.
