1. Evolution of Populations II

2. Genetic Drift A random change in allele frequency.
(certain individuals leave more descendants than others, just by chance)

3. Because of a random occurrence, the brown allele has become even more common.

4. Genetic Drift: Founder Effect
A small subgroup of a population migrates away, changing allele frequencies.

5. Stickleback Speciation
Lake: evolved away the lower spike.
Ocean: Still has the lower spike

6. Genetic Drift: Bottleneck Effect
A sharp decrease in population size, which could decrease genetic diversity.

7. Bottleneck Effect Example
In 1890, humans hunted the Northern Elephant Seal.
Numbers were reduced to 20 seals.
Their population numbers have since grown to over 30,000.
However, this population has less genetic diversity than the Southern Elephant Seals, who were not hunted as much.

8. Evolution vs. Genetic Equilibrium
Hardy-Weinberg Principle: Allele frequencies will remain constant as long as these 5 conditions hold true:
Random mating
Large population
No movement (in or out of population)
No mutation
No natural selection

9. Isolating mechanisms How does a new species develop? (speciation)
Reproductive Isolation occurs as new species evolve.
Members of two populations cannot or will not interbreed and produce fertile offspring.
Eventually. the populations become so different that they are considered a different species.

10. 3 Types of Reproductive Isolation
1. Behavioral Isolation
Different mating rituals or other behaviors so will not interbreed

12. 2. Geographic Isolation
Two populations are separated by geographic barriers, rivers, mountains, bodies of water.

13. 3. Temporal Isolation
Two or more species reproduce at different times.

14. Hinnies and mules are hybrids resulting from a cross between a horse and an ass or between a mare and a donkey, respectively. These animals are nearly always sterile due to the difference in the number of chromosomes between the two parent species. Both horses and donkeys belong to the genus Equus, but Equus caballus has 64 chromosomes, while Equus asinus only has 62. A cross will produce offspring (mule or hinny) with 63 chromosomes, that will not form pairs, which means that they do not divide in a balanced manner during meiosis.