Mader: Biology 8th Ed.

Population Genetics

• Genetic diversity in populations changes over generations

• Forces that cause populations to evolve• Allele and genotype frequencies over

generations

Mader: Biology 8th Ed.

Microevolution

• Change in gene frequencies between populations of a species over time

• Hardy-Weinberg Equilibrium• Stable, non-evolving population

Mader: Biology 8th Ed.

The nitty-gritty: p292 of text

• Random mating• No selection (no reproductive advantages)• No mutation• No migration• Large population

Mader: Biology 8th Ed.

Migration aka GENE FLOW

• Amount depends on:– Distance between populations– Ability of individuals/gametes to move

between populations– behavior

• No migration can result in reproductive isolation

Mader: Biology 8th Ed.

Genetic Drift: A result of small populations

• Chance events alter the gene pool

• Bottleneck effect• Founder effect• High level of inbreeding – loss of diversity in

the population

Mader: Biology 8th Ed.

Mader: Biology 8th Ed.

Figure 24.9 Ensatina eschscholtzii, a ring species

How do we define a “species”?

• Morphological species– Cryptic species

• Evolutionary species (fossils)• Biological species

Mader: Biology 8th Ed.

Reproductive Isolation

• Incapable of interbreeding…– Formation of new species…

• SPECIATION

Mader: Biology 8th Ed.

Mader: Biology 8th Ed.

Speciation

The splitting of one species into two or more species.

OR

The transformation of one species into a new species over time.

Mader: Biology 8th Ed.

Modes of Speciation1. Allopatric Speciation (Greek, different

fatherland)—a population forms a new species while geographically separated from its parent population.

reproductive isolation occurs.Examples: squirrels on either side of

the Grand Canyon; pupfish in springs in the deserts of California and Nevada; adaptive radiation in island chains.

Mader: Biology 8th Ed.

Modes of Speciation continued2. Sympatric Speciation (Greek, together,

fatherland)—a population develops two or more reproductively isolated groups without prior geographic isolation. Usually a mutation erects a reproductive barrier between the mutants and the parent population. Best evidence is found among plants where it can occur by means of polyploidy or by hybridization between two species followed by doubling of the chromosome number. These new plants can no longer reproduce with the parent species.

Mader: Biology 8th Ed.

Figure 24.6 Two modes of speciation

Mader: Biology 8th Ed.

Figure 24.7 Allopatric speciation of squirrels in the Grand Canyon

Mader: Biology 8th Ed.

Figure 23.9 Geographic variation between isolated populations of house mice

Mader: Biology 8th Ed.

Figure 24.8 Has speciation occurred during geographic isolation?

Mader: Biology 8th Ed.

Figure 24.13 Sympatric speciation by autopolyploidy in plants

Mader: Biology 8th Ed.

Figure 24.15 One mechanism for allopolyploid speciation in plants

Mader: Biology 8th Ed.

Adaptive Radiation• Is an example of allopatric speciation.• The rapid development from a single ancestral

species of many new species, which have spread out and become adapted to various ways of life.--as the parent population increases in size, daughter populations are subjected to the founder effect and the process of natural selection.--Examples: 13 species of Galapagos finches

20+ species of Hawaiian honeycreeper 500 species of Drosophila in

Hawaii

Mader: Biology 8th Ed.

Types of evolution

• Divergent• Parallel• Convergent

Mader: Biology 8th Ed.

Rates of Evolution

Mader: Biology 8th Ed.

Mader: Biology 8th Ed.

Mader: Biology 8th Ed.

Mader: Biology 8th Ed.

Mader: Biology 8th Ed.