1. MECHANISMS FOR EVOLUTION
CHAPTER 23

2. Objectives State the Hardy-Weinburg theorem
Write the Hardy-Weinburg equation and be able to use it to calculate allele and genotype frequencies
List the conditions that must be met to maintain Hardy Weinburg equilibrium

3. VOCABULARY POPULATION SPECIES GENE POOL GENE FLOW BOTTLENECK EFFECT
FOUNDER EFFECT
HETEROZYGOTE ADVANTAGE
HYBRID VIGOR
STABILIZING SELECTION
DIRECTIONAL SELECTION
DIVERSIFYING SELECTION
SEXUAL DIMORPHISM

4. POPULATION SPECIES GENE POOL
Localized group belonging to the same species
SPECIES
Naturally breeding group of organisms that produce fertile offspring
GENE POOL
Total aggregate of genes in a population at any one time
Most species are not evenly distributed over a geographic range. Individuals are more likely to breed with others from their population center

5. HARDY – WEINBURG THEOREM
Describes a NON-EVOLVING population
In the absence of other factors the segregation and recombination of alleles during meiosis and fertilization will not alter the overall genetic make-up of a population
The gene pool will remain constant unless acted upon by outside agents. No evolution!

6. Imagine an isolated wildflower population with the following characteristics
Diploid with both pink and white flowers
Pink is dominant A and white is recessive a
There are 480 pink flowers and 20 white
320 are AA
160 are Aa
(p + q)2 = 1
p + q = 1
p2 + 2pq +q2 = 1

7. p2 = frequency of AA 2pq = frequency of Aa q2 = frequency of aa
Calculate q2 first
There are 1000 alleles
AA x 2/plant = 640
Aa x 1/plant = 160
800
aa x 2/plant = 40
Aa – 160 x 1/plant =160
200
Frequency of A = 80% and a = 20%

8. Condition for Hardy-Weinburg
Large population
No net mutation
Isolated population
Random mating
No natural selection

9. MICROEVOLUTION LEADS TO MACROEVOLUTION

10. CAUSES OF MICROEVOLUTION
GENETIC DRIFT
BOTTLENECK EFFECT
FOUNDER EFFECT

11. GENE FLOW – genetic exchange between populations due to migration
Mutation – a new mutation that is transmitted in a gamete can immediately change the gene pool
NONRANDON MATING
Breed with other members of the “neighborhood” promotes inbreeding
Assortative mating – mate with others like themselves
NATURAL SELECTION

12. Variation within Populations
Most heritable variation is measured by
Quantitative characters (vary along a continuum ie. Height) are polygenetic
Discrete characters (pink or white) are located on a single gene
Polymorphism – two or more forms of a discrete character are represented in a population

13. GEOGRAPHICAL VARIATION
A cline is a graded change in some trait along a geographical axis.

14. MODES OF SELECTION