1. Unit 2: Change and Diversity in Life on Earth
Learning Goal 3: Explain the factors that can lead to speciation.

2. Phenotype Observable characteristics
(green eyes, brown hair, purple flowers, etc.)

3. Genotype
Genetic makeup of an organism determined by a pair of alleles.

4. All in the Genes The genetic make-up of an organism is known as
its genotype.
An organism’s genotype
and the environment in
which it lives determines
its total characteristic traits
i.e. its phenotype.
Genotype
Phenotype
commons.wikimedia.org/wiki/Image:DNA_double_helix_vertikal.PNG

6. DNA The double-helix structure of DNA was discovered in 1953.
This showed how
genetic information
is transferred from
one cell to another
almost without error.
Watson and Crick and their model of DNA
DNA replication
en.wikipedia.org/wiki/DNA

7. Gene Unit of hereditary information Located on a chromosome
Contains DNA
Genes are passed from parent to offspring.

8. Gene Pool
Consists of all the genes that are present in a population.

9. Mutation However, occasional mutations or copying errors
Types of mutation
However, occasional
mutations or copying errors
can and do occur when
DNA is replicated.
Mutations may be caused by radiation, viruses, or carcinogens.
Mutations are rare and often have
damaging effects. Consequently organisms have special enzymes whose job it is to repair faulty DNA.
Mutant fruitfly
upload.wikimedia.org/wikipedia/commons/7/79/Types-of-mutation.png humansystemstherapeutics.com/bb.htm

10. Genetic Variation Mutations
Any change in a sequence in DNA.
Few mutations lead to increased fitness.
Most mutations are harmful.
Species with greater genetic variability are more likely to adapt to changing environments.

11. Variation Nevertheless, some mutations will persist and
increase genetic variation
within a population.
Variants of a particular
gene are known as alleles.
For example, the one of
the genes for hair colour
comprises brown/blonde
alleles.
majorityrights.com/index.php/weblog/comments/racial_variation_in_some_parts_of_the_skull_involved_in_chewing/

12. Natural Selection population by sexual reproduction.
Mutant alleles spread through a
population by sexual reproduction.
If an allele exerts a harmful effect,
it will reduce the ability of the
individual to reproduce and the
allele will probably be removed
from the population.
In contrast, mutants with favorable
effects are preferentially passed on
Selection of dark gene
en.wikipedia.org/wiki/Image:Mutation_and_selection_diagram.svg

13. Natural Selection can affect the distribution of phenotypes in any of three ways:
Stabilizing Selection
Individuals at the middle of the curve have the greatest fitness.
Disruptive Selection
Individuals at either end of the curve have greater fitness than those in the middle.
Directional Selection
Individuals at one end of the curve have a higher fitness than those in the middle or other end.

14. Speciation Formation of a new species
Species: A group of similar organisms that breed together and produce fertile offspring.
Gene pools must become separated for them to become different species.

15. Tigon
Result of male tiger and female lion mating incaptivity. Offspring are infertile.
Separated both geographically and ecologically.

16. Liger
Result of male lion and female tiger mating in captivity. Offspring are infertile.

17. Speciation

18. Reproductive Isolation
Prevention of mating between formerly interbreeding groups. or
The inability of these groups to produce fertile offspring

21. Fig. 23.6
Four species of leopard frogs: differ in their mating calls. Hybrids are inviable.

22. Geographic Isolation Physical barrier divides a population
These two groups are not able to mate => leads to new species

23. These squirrels live on opposite sides of the Grand Canyon
These squirrels live on opposite sides of the Grand Canyon. This is an example of allopatric speciation.

24. Temporal Isolation
When two or more species reproduce at different times.

25. SPECIATION IN DARWIN’S FINCHES
SPECIAITON IN THE GALAPAGOS FINCHES OCCURRED BY:
FOUNDING OF A NEW POPULATION,
GEOGRAPHIC ISOLATION which led to … REPRODUCTIVE ISOLATION and
CHANGES IN THE NEW POPULATION’S GENE POOL due to COMPETITION.