EVOLUTION and SPECIATION

Gene Pool Combined genetic information (traits) of all members Allele frequency is number of times traits occur

Variation in Populations 2 processes can lead to this: Mutations - change in DNA sequence Gene Shuffling – from sexual reproduction

Genetic Drift changes populations Random change in allele frequency causes an allele to become common

Founder Effect: a cause of genetic drift caused by a limited number of individuals separating from a parent population

Gene Flow: genetic exchange due to the migration of fertile individuals or gametes between populations (reduces differences between populations)

Nonrandom mating: inbreeding and assortive mating (both shift frequencies of different genotypes)

Natural Selection: environment acts upon populations and determines traits best fit for success.

Sexual selection Sexual dimorphism: secondary sex characteristic distinction Sexual selection: selection towards secondary sex characteristics that leads to sexual dimorphism

Genetic Change in Populations Occurs when there is a change in the relative frequency of alleles

Phenotype Expression Depends on how many genes control that trait

Single-Gene vs. Polygenic Traits 2 Distinct Phenotypes Polygenic: Many Phenotypes (EG: tongue rolling)

Natural Selection: Peppered Moth

Conditions needed for Genetic Equilibrium

SPECIATION THE FORMATION OF A NEW SPECIES IF NEW SPECIES EVOLVE, THE POPULATIONS BECOME REPRODUCTIVELY ISOLATED REPRODUCTIVE ISOLATION – MEMEBERS OF TWO POPULATIONS CANNOT INTERBREED AND PRODUCE FERTILE OFFSPRING (HYBRIDS)

3 ISOLATING MECHANISMS…….. BEHAVIORAL ISOLATION- CAPABLE OF BREEDING BUT HAVE DIFFERENCES IN COURTSHIP RITUALS (Example: MEADOWLARKS) GEOGRAPHICAL ISOLATION – SEPARATED BY GEOGRAPHIC BARRIERS LIKE RIVERS, MOUNTAINS, OR BODIES OF WATER (Example: SQUIRREL) TEMPORAL ISOLATION – TWO OR MORE SPECIES REPRODUCE AT DIFFERENT TIMES OR SEASONS

Fig. 23.6 Four species of leopard frogs: They differ in their mating calls. Hybrids are inviable (die).

These squirrels live on opposite sides of the Grand Canyon These squirrels live on opposite sides of the Grand Canyon. This is an example of allopatric speciation.

Table 23.1a

Table 23.1b

Tigon Result of male tiger and female lion mating in captivity. Offspring are infertile. Separated both geographically and ecologically.

Liger Result of male lion and female tiger mating in captivity. Offspring are infertile.

Hawaiian Honeycreepers An possible example of adaptive radiation. These species may have diverged from a common ancestor (founder species). FOUNDER SPECIES

SPECIATION IN DARWIN’S FINCHES SPECIAITON IN THE GALAPAGOS FINCHES MAY HAVE OCCURRED BY: - FOUNDING OF A NEW POPULATION, - GEOGRAPHIC ISOLATION which led to -- REPRODUCTIVE ISOLATION and CHANGES IN THE NEW POPULATION’S GENE POOL due to COMPETITION.

Evidence Cited for Evolution Fossil Record Geographic Distribution of Living Species Homologous Body structures Similarities in Embryology

Evidence of Evolution? Fossil Record provides evidence that living things have become extinct Fossils show the history of life on earth and how different groups of organisms have survived over time

Marsupial Mammals Convergent Evolution Placental mammals and Flying Squirrel Sugar Glider Marsupial Mammals Convergent Evolution and Analogous Structures Placental mammals Mammalia Rat-like common ancestor?

Haeckel’s Drawings