SBI3U – Unit 3: Evolution
Date: ____________________
9.2 (Part 1) Speciation: How Species Form
Microevolution

Changes in the _____________________ of a population over time which result in relatively
_______________________________ to the organisms in the population
Macroevolution

Changes in _____________________, which are __________________ enough that, over time,
the newer organisms would be considered an entirely ___________________________.

The new organisms would be _______________________________________________,
assuming we were able to bring them together.
Species

Species - A group of actually or potentially ___________________________________________ that
ordinarily do not interbreed with other such groups even when there is opportunity to do so.
Speciation

The formation of _______________________________________________________________.

The formation of new species is also sometimes called _________________________________.
Types of Speciation
 Allopatric Speciation
The formation of two or more species often requires geographical isolation of subpopulations of the
species.
Only then can natural selection or perhaps genetic drift produce distinctive gene pools.
 Sympatric Speciation
Species diverge while inhabiting the same space and become reproductively isolated
What might keep two subpopulations from interbreeding when reunited geographically? There are
several isolating mechanisms. ____________________________________
Isolating Mechanisms
 Pre-zygotic – Before the zygote is formed
mating is __________________________
 Post-zygotic – After the zygote is formed
mating is not prevented, but the hybrids have _______________________________ (reduced chance of
survival)
Pre-zygotic Isolating Mechanisms – factors which cause species to mate with their own kind
Types of Pre-zygotic
Mechanisms
Description
Example
Post-zygotic Isolating Mechanisms – Genomic incompatibility, hybrid inviability or sterility.
Types of Pre-zygotic
Description
Mechanisms
Section 9.2 p. 363 #13 – 18, p. 365 #19 – 24
Example