Question

Most DNA-based phylogenetic analyses place humans and chimpanzees (including bonobos) as each other's closest relatives, but a persistent minority of studies place gorillas and chimpanzees as sharing a common ancestor that was not a human ancestor. The reason is incomplete lineage sorting, which simply means that ________.

1) the ancestral species of all great apes was genetically variable at some loci, and each descendant species lost different random combinations of ancestral alleles

2) the labs that sequenced great ape DNA made a simple procedural error

3) mitochondrial genes can become unlinked and be inherited by independent assortment

4) primate lineages are not completely reproductively isolated and can hybridize

5) coding regions of the primate genome are more likely to give false results than noncoding regions such as SINEs

Answer 1

Incomplete lineage sorting is the reason some studies show gorillas and chimpanzees sharing a common ancestor exclusive of humans. It occurs when an ancestral species has genetic variation, leading descendants to inherit different combinations of alleles, complicating phylogenetic analyses.

Step-by-step explanation:

The reason that some DNA-based phylogenetic analyses place gorillas and chimpanzees as sharing a common ancestor that was not a human ancestor, instead of humans and chimpanzees being each other's closest relatives, is due to incomplete lineage sorting. This phenomenon means that the ancestral species of all great apes was genetically variable at some loci, and each descendant species lost different random combinations of ancestral alleles. Essentially, because the ancestral population had genetic diversity, not all of its genetic traits were passed on uniformly to descendant species, leading to a pattern where some ancient alleles are found in one species but not in another, which can complicate the reconstruction of evolutionary relationships.