In parapatric
speciation, the new species evolve from
contiguous populations. A single species expands to inhabit a new and different environment. As selection worked on the
population in the new area, different genes would accumulate in it and the two populations would diverge to become adapted
to their respective environments. If they diverged almost to be different species, the border would be recognized as a
hybrid zone.
The mitochondrial
control region is the main region
involved in the regulation and initiation of mtDNA replication and transcription and the only major non-coding area in
animal mtDNA. Animal mt DNA is a circular molecule of 15-20 kb in length and in vertebrates it contains genes for 22
tRNAs, 2 rRNAs and 13 mRNAs coding for proteins involved in electron transport and oxidative phosphorylation.
A basal haplotype clade is a set of unique DNA sequences (SNPs or single
nucleotide polymorphisms) shared by the greatest number (all) members of a sub-group within a
sampled population. For example, two sequenced DNA fragments from different individuals of a single species, AAGCCTA to AAGCTTA, contain a
difference in a single nucleotide. In this case we say that there are two alleles : C and T,
or 2 version of the same DNA sequence. Sets of these alleles make up the haplotype.
Maximum likelihood estimates a statistical test
A mismatch distribution is a tabulation of the number of pairwise differences
among all DNA sequences in a sample.
In a population that has been stationary for a long time these distributions
from nonrecombinant DNA sequences
become ragged and erratic, whereas a population that has been growing
generates mismatch distributions that
are smooth and have a peak. The position of the peak reflects the time of the
population growth. The signature of
an ancient population expansion is apparent even in the low-resolution mtDNA
typings described by Merriwether
et al. (1991). The smoothness of the mismatch distribution, an indicator of
population expansion, is hardly
affected by population structure, whereas mean sequence divergence increases
in a pooled sample from highly
isolated subpopulations.
Glossary to
understand abstract