BIO 201 - Quiz 2 (2.1, 2.2, 2.4(first 5 objs))

importance of variation to a population

= differences among individuals in a population

• essential for natural selection

• without variation:

  • no individuals have advantages over others

  • population can no adapt to enviormental changes

• variation increases

  • survival chances of the population

  • ability to respond to disease, climate change, predators, etc

  • Evolution doesn’t create traits when needed

  • The traits must already exist as variation in the population

    • Then natural selection “chooses” the individuals with helpful traits

two types of variation

1. genetic (heritable) variation

• caused by differences in DNA

• passed from parents to offspring

• example: eye color, blood type

2. environmental (non-heritable) variation

• caused by environment, not genes

• not passed to offspring

• example: tan skin, muscle size from working out

heritable vs. acquired traits (HERITABLE TRAITS)

• controlled by genes

• passed to offspring

• example: fur color in animals

heritable vs. acquired traits (ACQUIRED TRAITS)

• developed during life

• NOT passed on genetically

• example: scars, learned behaviors

why is heritable variation required for evolution?

• evolution = change in allele frequencies over generations

• only heritable traits affect allele frequencies

• natural selection acts on genetic variation, not acquired traits

graphing evolutionary change

• x-axis: generations (time)

• y-axis: frequency of a trait or allele

common patterns of graphing

1. directional selection

• traits shift in one direction

2. stabilizing selection

• intermediate traits favored

3. disruptive selection

• extreme favored over average

  • evolution is shown as change in trait frequency over time

why do species look similar?

common ancestry

why are species adapted to environments?

natural selection

why do some species go extinct?

environmental change + inability to adapt

why is biodiversity higher in some areas (like tropics)?

longer evolutionary time + stable environments

challenges in reconstructing evolutionary history

• incomplete fossil records

  • not all organisms fossilize

• convergent evolution

  • unrelated species evolve similar traits

• limited or degraded DNA

• extinction

  • missing links in evolutionary tree

• homoplasy

  • traits appear similar but evolved independently

node

common ancestor

• the closer the shared node —> the more closely related

branch

evolutionary lineage

clade

ancestor + all descendants

sister taxa

closest relatives

root

base (common ancestor of all taxa)

outgroup

• species known to be less closely related

• helps determine:

  • ancestral traits (present in outgroup)

  • derived traits (new traits not in outgroup)

• trait in outgroup = ancestral

• trait only in ingroup = derived

reconstructing phylogeny using molecular data + parsimony

• compare DNA / protein structures

• count difference

parsimony principle

• choose tree with fewest evolutionary changes

• simplest explanation = most likely

drawing phylogeny

1. identify traits (or DNA differences)

2. determine shared derived traits

3. group organisms by similarity

4. draw tree with

• common ancestors at nodes

• derived traits along branches

• important: phylogenies are hypotheses, not absolute facts