Chapter 17: Processes of Evolution Unit 6: Evolution

Case Study: Rise of the Super RatsCase Study: Rise of the Super Rats  Rats are one of the most notorious pests of all time  Cost us about ____________ each year  Rodenticide warfarin: very effective when first used  Rats developed resistance – inherited gene that made the chemical ineffective  This is an example of: __________________________________

Variation in PopulationsVariation in Populations  _______________ : one group of individuals of the same species in a specified area  Species share:  Morphological traits  Physiological traits  Behavior traits  Populations show variation in traits:  Qualitative: __________________________  Quantitative: _________________________

The Gene PoolThe Gene Pool  The genes of a population comprise the _______ ________, a pool of genetic resources  Alleles are the primary source of variation in appearance  Polymorphism: occurs when genes have three or more alleles that persist in a population with a frequency of at least 1%  Example: _______________________  ________________ : two distinct traits  Example: male / female

Mutations  Mutations are the source of new alleles  We can predict average mutation rates  In humans: ________ mutations per person per generation  Many mutations give rise to structural, functional, or behavioral alterations that reduce an individual’s chance of surviving and reproducing

Mutations  Mutations can be:  ____________ : usually arise from drastic changes in the phenotype  _____________: alter the base sequence of DNA but have no effect on survival or reproduction  ______________: enhances the survival or reproduction – occurs every so often  Natural selection will favor the transmission of beneficial mutations on to the next generations

Stability and Change in Allele FrequenciesStability and Change in Allele Frequencies  Researchers typically track _____________ _________________ in populations (how often a certain allele occurs)  The relative abundance of alleles of a given gene among all individuals of a population  For a starting point, they use a reference called genetic equilibrium, when a population is not evolving with respect to a certain gene  Genetic equilibrium can ONLY be reached when five conditions are met

Genetic EquilibriumGenetic Equilibrium  Genetic equilibrium can occur only when:  Mutations do not occur  The population is infinitely large  The population stays isolated from all others of the same species  Mating is random  All members of the population survive and produce the same number of offspring  In nature, _______________________________

Microevolution  If all 5 conditions are never met, change is occurring within a population  Results in small-scale changes in the population’s allele frequency; called __________________  Four processes of microevolution:  mutation  natural selection  genetic drift  gene flow

When is a population not evolving?When is a population not evolving?  The Hardy-Weinberg Formula can be used to track whether a population is in genetic equilibrium or not  A mathematical formula which tracks allele frequency for a specific trait  Applied rules of probability to sexually reproducing populations and found that the gene pool can only be stable when __________________________  Researchers can use the formula to estimate the frequency of carriers of alleles that cause genetic traits and disorders

Hardy-Weinberg Genetic EquilibriumHardy-Weinberg Genetic Equilibrium  Hardy-Weinberg formula: p pq + q 2 = 1 p + q = 1 where p and q are the frequencies of alleles A and a  You can draw this on a Punnett square:

Natural SelectionNatural Selection  Natural selection: the differential survival and reproduction among individuals  Natural selection influences all levels of biological organization  Selection can be:

Directional SelectionDirectional Selection  Directional selection occurs when allele frequencies shift in a _____________________  Forms at one end of the range of phenotypic variations become more common than the intermediate forms  Examples:  Peppered Moth, pocket mice (predation)  Resistance to antibiotics

Directional SelectionDirectional Selection  Butterfly wing color: medium-blue is between two phenotypic extremes (white and dark purple)  Orange arrows identify which forms are being selected against over time Figure 17.5, page 270

Peppered MothPeppered Moth  Peppered moth: a classic example of the directional selection process  Feed at night and rest on tree trunks during day  Light gray lichens grew on trees  In preindustrial England, light colored moths were the most common  Due to air pollution starting in 1850s, the dominant allele shifted to dark colored moths  Air pollution was _________________________

Peppered MothPeppered Moth  Since the advent of pollution controls starting in 1950s, allele frequency has begun to shift back to light colored moths Figure 17.6, pg 271

Pocket MicePocket Mice  Rock pocket mice in Arizona are another example of directional selection  Light brown granite; dark basalt (lava rock) Figure 17.7, pg 271

Resistance to AntibioticsResistance to Antibiotics  Human activity can also influence directional selection  Antibiotics: toxins that kill bacteria by interfering in physiological processes  Since 1940s, have been widely prescribed in the U.S.  Overuse of antibiotics puts tremendous selection pressure on bacteria  Bacteria divide quickly and form huge populations with great genetic variation  E. coli can divide every _________________  Likely that some will survive antibiotic treatment  Resistant strains are becoming the norm

Selection Against or in Favor of Extreme Phenotypes  Stabilizing Selection: works against phenotypes at the fringes of a range  Disruptive Selection: favors phenotypes at the fringes of a range

Stabilizing SelectionStabilizing Selection  Stabilizing selection: intermediate forms of a trait in a population are favored  Does NOT _______________________________  Examples:  Birth weight for babies – mid-sized babies selected for most often  Body mass size of sociable weaver birds  Body mass represents a trade-off between risks of starvation and predation

Stabilizing SelectionStabilizing Selection Stabilizing eliminates the ______________ Figure 17.8a, pg 272

Disruptive SelectionDisruptive Selection  Disruptive selection: forms at both ends of a range of variation are favored  Intermediate forms are ______________________  Example: selection for bill size in black-bellied seedcracker finch in Africa  Females and males have either large or small bills (no intermediate ones)  2 different types of plants: hard or soft seeds  Feeding performance maintains this dimorphism of beak size

Disruptive SelectionDisruptive Selection Disruptive selection eliminates _______________________ Figure 17.8b, pg 272

Modes of Natural SelectionModes of Natural Selection Fig 17.4, page 269