1. Chapter 16

2. Section 1

3.  Population genetics – the study of evolution from a
genetic point of view
 Microevolution – a change in the collective genetic
material of a population

4.  Variations in genotype arise in three main ways
 Mutation – a random change in a gene that is passed on
to offspring
 Recombination – the reshuffling of genes in a diploid
individual
 Random pairing of gametes – the union of a
particular pair of gametes is matter of chance

5.  Gene pool – total genetic information available in a
population
 Allele frequency – number of a certain allele divided by
the total number of alleles of all types in the population
 Phenotype frequency - number of individuals with a
particular phenotype divided by the total number of
individuals in the population
 All allele and phenotype frequencies must add up to 1

7.  Genotype frequencies remain the same from
generation to generation unless acted on by outside
influences
 Known as Hardy-Weinberg Genetic
Equilibrium, and it is based on a set of assumptions
about an ideal hypothetical population that is not
evolving

8. Conditions required for genetic equilibrium:
1. No mutations
2. Individuals neither enter nor leave the population
3. The population is large
4. Individuals mate randomly
5. No natural selection

9. Section 2

10.  Spontaneous mutations occur constantly, at very low
rates under normal conditions
 If an organism is exposed to mutagens, mutation rates
can increase significantly
 Mutations can affect genetic equilibrium by producing
totally new alleles for a trait

11.  Gene flow – process of genes moving from one
population to another
 Occurs through migration of individuals, dispersal of
seeds or spores, etc.

12.  Genetic Drift – phenomenon by which allele
frequencies in a population change as a result of
random events, or chance
 Small populations usually exhibit a large degree of
genetic drift
 Large populations maintain a small degree of genetic
drift
 Founder effect - occurs when a new colony is started
by a few members of the original population

13.  Mate selection is often influenced by geographic
proximity and traits that are similar to their own
 Sexual selection is the tendency for females to
choose the males they mate with based on certain
traits

14.  Stabilizing selection – individuals with the
average form of a trait have the highest fitness

15.  Disruptive Selection – individuals with either
extreme variation of a trait have greater fitness than
individuals with the average form of a trait

16.  Directional Selection – individuals that display a
more extreme form of a trait have greater fitness than
individuals with an average form of the trait

17. Section 3

18.  Speciation – the process of species formation
 Results in closely related species

19.  Morphological Concept of Species
 Species defined primarily according to structure and
appearance
 Limitations:
 Phenotypic differences among individuals in a single
population
 Some organisms that appear different enough to belong to
different species interbreed

20.  Biological Species Concept
 A species is a population of organisms that can
successfully interbreed but cannot breed with other
groups
 Limitations:
 Not useful for extinct organisms or for organisms that do not
reproduce sexually
 Our modern definition of species includes components
of both the morphological and biological species
concepts

21.  Speciation begins with isolation
 In isolation, two parts of a formerly interbreeding
population stop interbreeding

22. Geographic Isolation Allopatric Speciation
 Physical separation of  Happens when species
members of a population arise as a result of
geographic isolation

23. Reproductive Isolation Sympatric Speciation
 Results from barriers to  Occurs when two
successful breeding subpopulations become
between population reproductively isolated
groups in the same area within the same
 Caused by: geographic area
 Disruptive selection  Ex: 2 types of insects
 Unrecognized mating that live on different
call plants in the same area
 Different times of peak
mating activity