Chimpanzee Genome
559
Tab. 1
Comparative DNA sequence data sets to resolve the phylogeny of humans, chimpanzees,
and gorillas.
Number of
genomic loci
Total compared
length [bp]
Numbers of loci supporting phylogeny
a
(H,C)G
(H,G)C
(C,G)H
(H,C,G)
45
46 855
23
8
8
6
53
24 237
31
10
12
0
51
62 530
26
10
12
3
Notes
:H:human;C:chimpanzee;G:gori
l
la.
a
The grouped species shared a common ancestor after the separation of the third species.
(H,C,G) represents those loci that could not resolve the phylogeny (trifurcation).
sequences (gene trees) can differ from the
species tree. Mainly two problems need
to be considered: Frst, sampling only a F-
nite number of nucleotides from a locus
produces a stochastic sampling error and
thus, bears a probability to infer an incor-
rect gene tree; second, the model where
the time point at which corresponding
DNA sequences from different species last
shared a common ancestor is identical to
the time point of speciation is too sim-
plistic. ±igure 3 shows an example where
the presence of sequence variants of the
analyzed locus in the ancestral popula-
tion in combination with lineage sorting
can cause gene tree–species tree incon-
gruities. Especially for species where the
amount of genetic polymorphisms in their
ancestral population was high and the time
between subsequent speciation events was
short – both seem to apply to the common
ancestor of chimpanzees, humans, and
gorillas – lineage sorting renders phyloge-
netic conclusions based on only a single
locus unreliable. Therefore, a joint analy-
sis of multiple independent DNA sequence
data sets was required to eventually end the
debate concerning the phylogeny of homi-
noids with sufFcient statistical support.
Humans are the closest relatives of chim-
panzees and based on molecular evidence,
both species separated approximately 4.6
to 6.2 million years ago. The likewise es-
timated date for the speciation of gorillas
ranges from 6.2 to 8.4 million years be-
fore present.
1.3
Genetic Diversity
DNA sequence evolution is a continual
process in time. Therefore, DNA sequence
Fig. 3
Gene tree–species tree
incongruities due to ancestral
polymorphisms and lineage
sorting. The gray and black lines
represent the species tree (true
phylogeny) and the gene tree
respectively.
Time
Gorilla
Chimp
Human
Speciation
Speciation
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