Biology Reference
In-Depth Information
Homo
Homo
Pan
Pan
Addition of
juxtacentromeric
heterochromatin
(secondary constriction)
Fusion
Gorilla
Gorilla
Paracentric inversion
Pongo
Pongo
Pericentric inversion
P
apionini
Papionini
Cebidae
Cebidae
Pericentric
inversion
Heterochromatin
changes
Cercopithecini
Cercopithecini
Fission
Changes in
centromere location
by activation/inactivation
mechanisms
Pericentric inversion
Fusion
1
2 chromosomes
2
Homo
Homo
Pan
Pan
Addition of terminal
heterochromatin
Gorilla
Gorilla
Addition of terminal
heterochromatin
Pongo (Sumatra)
Paracentric
inversion
Pongo
Pericentric inversion
Pericentric inversion
Pericentric
inversion
Pongo (Borneo)
Papionini
Papionini
Cebidae
Cebidae
Pericentric
inversion
Pongo
(Borneo)
Cercopithecini
Cercopithecini
Centric fission
At least 2
chromosomes
Complex
structural
reorganizations
Complex
reorganizations
Papio
Fusion (
)
At least 2 chromosomes
At least 2 chromosomes
3
7
Figure 2.5.
Chromosome evolution in primates. Evolution of chromosomes 1, 2, 3, and 7.
The main reorganizations that took place are indicated in the phylogenetic trees (redrawn
from Clemente
et al.,
1990).
at 2q13 rather than by translocation after chromosome breakage. This fusion has
subsequently been confirmed by chromosome painting (Arnold
et al
., 1995;
Wienberg
et al
., 1994) and since it accounts for the reduction in chromosome
number from 24 pairs in the great apes (chimpanzee, orangutan, and gorilla) to 23
pairs in humans, it must have been a relatively recent event. Fusion must have
been accompanied or followed by inactivation or removal of one of the ancestral
centromeres. Consistent with this postulate, IJdo
et al
. (1991) found evidence by
hybridization for the residual presence of an ancestral centromere at 2q21.
Clearly, this reduction in chromosome number would have been a critical event
during the speciation process; if it was not in itself responsible for bringing about
reproductive isolation, it would certainly have helped to maintain it.
Another major chromosomal rearrangement to have occurred in the great apes
is to be found in the gorilla. Using human chromosome-specific libraries as
probes for
in situ
hybridization, Stanyon
et al
. (1992) described a reciprocal
