1. Chapter 11
11.1 & 11.3

2. Starter Write & Answer
Name and graph the three ways natural selection can change the distribution of traits.
How might the overfishing of large pink salmon affect salmon size in future generations? Which pathway of natural selection is this?
Woodpeckers with extremely large beaks are unable to fit their beaks into small holes and retrieve bugs. Woodpeckers with very small beaks are unable to reach bugs that have crawled to the back of holes and tunnels. What will happen to the woodpecker population? What pathway of natural selection is this?

3. Genetic Variation in Populations
A population shares a common gene pool
gene pool - the combined alleles of all the individuals in a population

4. Genetic Variation increases the probability that some individuals will survive
Genetic variation leads to phenotypic variation
Phenotypic variation is necessary for natural selection
Genetic variation is stored in the population’s gene pool

5. Allele Frequencies measure genetic variation
measures how common an allele is in a population
can be calculated for every allele in a gene pool

6. Genetic variation has several sources:
Mutation (a random change in DNA) – can form a new allele, can be passed on to offspring
Recombination (parents’ alleles recombined in offspring)

7. Natural Selection is not the only mechanism through which populations evolve
Gene Flow : the movement of alleles between populations
Occurs when individuals join other populations and reproduce
Gene flow keeps neighboring populations similar
Low Gene Flow increases the chances that two populations will evolve into different species

8. Genetic Drift
Genetic drift is a change in allele frequency due to chance
Bottleneck Effect: a random/destructive event reduces a population’s size
The Founder Effect: genetic drift that occurs after a small number of individuals colonize a new area

9. Genetic Drift
The illustration to the right represents the bottleneck effect. An event reduces the population size, reducing the variation. Here, the “red” alleles are eliminated.
The illustration to the left represents the founder effect – a new population of flowers is founded, without the “orange” allele.

10. Genetic Drift has negative effects on populations
less variation, less likely that individuals can adapt
harmful alleles may be more common in the population

11. Sexual Selection
Sexual Selection occurs when certain traits increase mating success
Occurs due to the higher cost of reproduction for females than males
Males produce sperm continuously
Females are more limited in number of potential offspring

12. Two types of Sexual Selection
Intrasexual selection: competition among males
Intersexual selection: males display certain traits to females