1. Speciation & macroevolutionary change

2. Allopatric Speciation
Most common form of speciation
Due to geographically isolation
- Gene flow between them stops between populations
- Genetic differences emerge
- Small populations = FOUNDER EFFECT (different allelic frequencies when populations separated)

4. Sympatric Speciation
Populations in same habitat become reproductively isolated from each other
Related to polyploidy (offspring born with twice the normal number of chromosomes!)
These individuals can’t mate with original population
Super rare!
Mostly seen in plants as it’s easier for them to self-fertilize

5. Comparing Allopatric & Sympatric Speciation

6. 1. Heterochrony
Developmental change in the timing of events leading to changes in size and shape
Timing of when genes are expressed
Two main components:
(i) the onset and offset of a particular process
(ii) the rate at which the process operates
*Allometric growth and Paedomorphism are examples of heterochrony! Let’s take a look…

7. 2. Allometric Growth Varied rates of growth in certain organisms
Ex. the claw of fiddler crab grows much larger and faster than the rest of the crab

8. 3. Paedomorphism
Organism becomes reproductive sooner than an ancestral species (due to mutation)
Body is still in its juvenile form when the animal becomes sexually mature; body development then STOPS
Ex. Mud puppy
(salamander)
retains juvenile
gills externally

9. Ex. Many domestic dog breeds (Canis lupus familiaris), derived from wolves (Canis lupus), exhibit paedomorphy with respect to adult wolves

10. 4. Homeotic Genes
Genes which regulate the development of anatomical structures
Regulation is done via the programming of various transcription factors by the homeotic genes
These affect genes through regulatory genetic pathways

11. Imagine what can happen if a mutation occurs to one of these…
Example: Hox Genes
Group of related genes that control body plan of an embryo along head to tail axis 
Hox proteins determine type of segment (ex. Legs, wings, antennae, etc)
Initiate identity of a segment but not the actual segment, itself
Imagine what can happen if a mutation occurs to one of these…