Chapter 17: Processes of EvolutionUnit 6: Evolution

Case 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 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 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 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 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?

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 Equilibrium

Hardy-Weinberg formula:p2 + 2 pq + q2 = 1p + q = 1

where p and q are the frequencies of alleles A and a

You can draw this on a Punnett square:

Natural Selection Natural selection: the differential survival

and reproduction among individuals Natural selection influences all levels of

biological organization Selection can be:

Directional 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 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 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 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 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 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 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 Selection

Stabilizing eliminates the ______________

Figure 17.8a, pg 272

Disruptive 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 Selection

Disruptive selection eliminates _______________________

Figure 17.8b, pg 272

Modes of Natural Selection

Fig 17.4, page 269