Types of speciation
*remember, speciation is
the formation of a new
species
 1. sympatric
 2. allopatric
sympatric
 New species develops when
members of a population
develop a genetic difference
that prevents them from
reproducing with members of
the original species.
 Occurs due to reproductive
isolation, not geographic
 Far more common in plants
Polyploidy
 is the presence of extra sets of
chromosomes due to accidents during
cell division
 Many important crops (oats, cotton,
potatoes, tobacco, and wheat) are
polyploids
Sympatric speciation by polyploidy
(in plants)
 Sometimes hybrids between two parental
flowering plants are formed.
 This can happen because plants can‘t choose
whom to mate with (i.e. pollinators or wind may
move pollen between flowers of different
species
 Hybrids may be sterile if paternal and maternal
chromosomes are incompatible and cannot pair
in meiosis.
 But sometimes, chromosome sets “accidentally“
double (polyploidy)
 This doubling results in compatible partners
 Plants can self-pollinate, produce seeds, and so
propagate: a new species has formed
 Between 30 and 50% of angiosperm plant species
Allopatric speciation
 Occurs when two populations
are geographically isolated
from one another. They are
separated by distance or an
impassable barrier.
Allopatric speciation
 Occurs when a physical barrier
cuts a breeding population in two.
 Example: Grand Canyon squirrels
Kaibab squirrel
Abert squirrel
Figure 24.5
(a) Allopatric speciation.
A population forms a
new species while
geographically isolated
from its parent population.
(b) Sympatric speciation.
A subset of a population
forms a new species
without geographic
separation.