Assessing character state polarity with ape chromosomes
The following figure (Yunis and Prakash 1982 Science 215:1525-1530) shows a stylized representation of G-banded chromosomes of four great ape species, namely human, chimp, gorilla, and orangutan. Taken individually, each set of homologs could be used to reconstruct rearrangements that have taken place during the divergences of the four species.
|For example, the difference between human and chimp chromosomes 4 could be explained by a pericentric inversion.|
See if you can identify, in homolog sets 1-4, cases that represent examples of insertion, telomeric fusion, inversion, or translocation. Can you use each set of homologs to infer a phylogeny of the apes?
1. How would we determine what bands represents states of a homologous character?
2. What can we infer about the polarity of the states (pleiomorphies, apomorphies)?
3. Are the four phylogenies congruent?