Evolution of chromosomes

Evolution occurs also by structural rearrangements
of the genome at the chromosomal level.
Related species, e.g., mammals, differ by the
number of their chromosomes and chromosomal
morphology, but not by the number of
genes, which often are conserved to a remarkable
degree. The human chromosomes 2 and 5
are shown in comparison with the corresponding
chromosomes in three closely related primates,
chimpanzee, gorilla, and orangutan. The
human chromosome 2 appears to have evolved
from fusion of the two primate chromosomes.
The differences in chromosome 5 are much
more subtle. The orangutan chromosome 5
differs from that of man and the other primates
by a pericentric inversion. The banding pattern
of all primate chromosomes is remarkably similar.
This reflects their close evolutionary relationship.