1. The process of speciation
Section 17.3

2. How does on species become two?
It takes more than just a change in allele frequency caused by genetic drift and natural selection

3. Speciation Speciation is the formation of a new species
Interbreeding links members of a species genetically
Genetic changes can spread through a population over time
But it is possible to split the gene pool
If members of the population stop breeding with each other
The genetic changes will not spread from one group to another
Because the two populations can no longer interbreed, reproductive isolation occurs
When two populations become reproductively isolated, they can evolve into two separate species.

4. Reproductive isolation can occur in a variety of ways
Behavioral isolation
When two population capable of interbreeding develop different courtship rituals or other behaviors
Example – mating song of meadowlarks
Geographic isolation
When two populations are separated by a geogrpahic barrier – such as rivers, mountains or bodies of water
Do not apply to all organisms at any one time, may isolate one organism but link another – e.g. flood
Example – squirrels in the grand canyon
Temporal isolation
When two or more species reproduce at different times
Example – orchids flowering in a forest.

5. Speciation and Darwin’s finches
How have the founder effect and natural selection produced reproductive isolation that could have lead to speciation amongst Galapagos finches?
What has been observed by studying the Galapagos finches is essentially the culmination of all aspects of speciation
Founder effect
Geographic isolation
Changes in the gene pool
Behavioral isolation
Ecological competition

7. Writing assignment: Explain how natural selection and behavioral isolation may have lead to reproductive isolation in Darwin’s finches

8. Molecular evolution
Section 17.4

9. Timing lineage splits
Molecular clock: Stretches of DNA are compared to mark the passage of evolutionary time
Mutation rates in DNA are used to estimate the time that two species have been evolving independently
Neutral mutations have no effect on phenotype, and tend to accumulate in the DNA of different species at a similar rate
By comparing DNA sequences, it is possible to reveal how many mutations have occurred independently in each group
The more differences, the more time has passed since a common ancestor

10. How do you calibrate the clock?
Each genome will have many molecular clocks that ‘tick’ at different rates
Some genes accumulate mutations faster than others
Like second, minute and hour hands on a watch
Different ’clocks’ are used to compare different common ancestors
Researchers check the accuracy of the clock by trying to estimate how often mutations occur
Done by comparing the number of mutations in a particular gene in species whose age has been determined by other methods

11. Where do new genes come from?
Modern genes (our 25,000 working genes) probably descended from a much smaller number in the earliest life forms - How?
One way is through the duplication and then modification of existing genes

12. Copying Genes Most organisms have several copies of various genes
Sometime two copies, sometimes thousands of copies
Where do they come from? Why are they there?
Crossing over of Homologous chromosome sometimes involves the unequal swapping of DNA
One chromosome gets extra DNA
This can carry part of a gene, a full gene, or a longer length chromosome.

13. Duplicate Genes Evolve
Extra copies of genes can undergo mutations that change their function
The original gene is still there, so the new genes evolve without affecting the original gene function or product
Multiple copies of duplicated genes can turn into a group of related genes or a gene family
Members will produce similar, yet slightly different proteins
Our body produces a number of proteins that carry oxygen – the globin family
HOX genes are another gene family

14. Hox genes and evolution
Hox genes determine which parts of an embryo develop arms, legs or wings
Groups of hox genes control the size and shape of these structures
Homologous hox genes shape the bodies of both insects and humans
Although our last common ancestor was over 500 million years ago!
Small changes in Hox gene activity during embryological development can produce large changes in adult animals
One small change to a Hox gene can lead to a large evolutionary difference
Example – UBX gene changes number of legs between insects and crustaceans

15. Timing is everything
Every part of an embryo starts to grow at a specific time, grows for a specific time and stops growing at a specific time
Small changes in starting and stopping times can make a big difference to organisms
Small timing changes can be the difference between long slender fingers and short stubby fingers
Evolutionary development is a new and exciting area of Biology!