Chapter 8

Question 1

Gene pool

Answer 1

• frequency of each allele within a population
• evolution is the change in the gene pool of a population over time

Question 2

Define Hardy-Weinberg principle + 5 conditions

Answer 2

• in large populations in which only random chance is at work, allele frequencies are expected to remain constant from generation to generation
  1. no natural selection
  2. population must be very large
  3. no mutations
  4. population must be isolated from other populations (no immigration or emigration)
  5. random mating and no horizontal gene transfer

Question 3

Selective pressures

Answer 3

• may result from any number of biotic or abiotic factors
• can result in different patterns of natural selection

Question 4

Directional selection

Answer 4

• a selection that favors individuals with a more extreme variation of a trait
• results in a shift away from the average
• common in artificial selection

Question 5

Stabilizing selection

Answer 5

• occurs when the average phenotype within a population is favored
• selection against extreme traits

Question 6

Disruptive selection

Answer 6

• favours individuals with variations at opposite extremes of a trait over the average phenotype; favours more than one phenotype

Question 7

Sexual selection

Answer 7

• favours any traits that specifically enhance the mating success of an individual
• leads to males and females of a species evolving appearances and behaviours that differ from each other (sexual dimorphism)

Question 8

Genetic Drift

Answer 8

changes to allele frequency as a result of chance; effects small population more than large population

Question 9

Bottleneck Effect

Answer 9

• occurs when a population undergoes a drastic reduction in size
• caused by chance events (volcanic eruption, hurricane)
• bad luck, not bad genes
• can cause big losses of genetic variation in small populations

Question 10

Example of Bottleneck Effect

Answer 10

• Northern elephant seals have reduced genetic variation
• hunting reduce their population size to 20 individuals at the end of the 19th century
• have since rebounded but have less genetic variation than southern elephant seals

Question 11

Founder effect

Answer 11

• results when a small number of individuals separate from their original population and establish a new population
• this small population size means that the new population may have…
  - reduced genetic variation from original population
  - non-random sample of the genes in original population

Question 12

Example of Founder Effect

Answer 12

• Afrikaner population of dutch settlers in south africa descended from a few colonists
• Today, Afrikaner population have a high frequency of Huntington’s disease because the original settlers carried the gene for Huntington’s disease

Question 13

Gene flow + 2 types

Answer 13

occurs when individuals migrate to/from one population to/from another and interbreed
immigration - individuals enter a population
- possible addition of new genetic material to the gene pool of a population
emigration - individuals leave a popluation
- possible removal of genetic material from the gene pool of a population

Question 14

Mutations

Answer 14

random genetic mutations can introduce new alleles into a gene pool

Question 15

Microevolution

Answer 15

changes in gene (allele) frequencies and phenotypic traits within a population over a relatively short period of time

Question 16

Speciation

Answer 16

the formation of a new species

Question 17

Macroevolution

Answer 17

• major evolutionary change
• applies to the evolution of whole taxonomic groups over long periods of time

Question 18

Biological species concept

Answer 18

• species are groups of individual that can mate and produce fertile offsprings under normal circumstances
• members of different species are reproductively isolated from one another
• popluations have no gene flow between them

Question 19

Reproductive isolating mechanism

Answer 19

• any behavioral structural or biochemical trait that prevents individuals of different species from reproducing together
  Prezygotic mechanisms
  - prevents interspecies mating and fertilization
  Post-zygotic mechanisms
  - prevents maturation and reproduction in offspring from interspecies reproduction (hybrid)

Question 20

Reproductive isolating mechanism

Answer 20

• any behavioral structural or biochemical trait that prevents individuals of different species from reproducing together
  1. Prezygotic mechanisms
  - prevents interspecies mating and fertilization
  2. Post-zygotic mechanisms
  - prevents maturation and reproduction in offspring from interspecies reproduction (hybrid)

Question 21

Prezygotic mechanism - Behavioural isolation

Answer 21

• different species use different courtship and other mating clues to find and attract a mate
• example: male frogs of different species have unique calls that attract females of only their own species

Question 22

Prezygotic mechanism - Temporal isolation

Answer 22

• different species breed at different times of the year
• example: frogs in the same pond may reproduce at different times of the year

Question 23

Prezygotic mechanism - Ecological (Habitat) Isolation

Answer 23

• very similar species may occupy different habitats within a region
• example: two closely related antelope squirrels are on opposite sides of the Grand Canyon

Question 24

Prezygotic mechanism - mechanical isolation

Answer 24

• differences in morphological features may make two species incompatible
• example: pollen sacs in orchids becomes attached to specific insects and not others

Question 25

Prezygotic mechanism - gametic isolation

Answer 25

- males gametes may not be able to recognize and fertilize an egg of a different species - example: many marine animals (ie. coral) release their sperm into open water. The sperm recognize eggs of their own species through chemical markers on the surface of the eggs

Question 26

Postzygtoc mechanism - zygotic mortality

Answer 26

- mating and fertilization are possible. zygotes formed will not survive, embryos will not develop to maturity - example: some species of sheep and goat are able to mate, but the zygote is not viable

Question 27

Postzygotic mechanism - hybrid inviability

Answer 27

- a hybrid individual develops but either dies before birth or, if born alive, cannot survive to maturity - example: when tigers and leopards are crossed, the zygote begins to develop but the pregnancy ends in a miscarriage or still born offspring

Question 28

Postzygotic mechanisms - hybrid infertility

Answer 28

- hybrid offspring remain healthy and viable but are sterile - example: mules are the sterile (63 chromosomes) hybrids offspring of a horse-donkey cross

Question 29

Types of Speciation

Answer 29

allopatric speciation - the formation of a new species as a result of evolutionary changes following geographic isolation sympatric speciation - the evolution of populations within the same geographic area into separate species

Question 30

Adaptive Radiation

Answer 30

- The relatively rapid evolution of a single species into many new species, filling a variety of formerly empty ecological niches - Occurs when a variety of new resources become available that are not being used by other species - example: Darwin’s finches

Question 31

Divergent evolution

Answer 31

- the large-scale evolution from a common ancestor into many different forms - The pattern of speciation (allopatric, sympatric, adaptive radiation) follow this pattern

Question 32

Convergent evolution

Answer 32

the evolution of similar traits in very distantly related species examples : - Birds and insects both have wings yet they are evolved from different ancestors - Sharks and dolphins have similar body shapes

Question 33

Coevolution

Answer 33

- a process in which one species evolves in response to the evolution of another species - Include, predator-prey, plant-pollinator and parasite - hosts relationships