Ch 6 Exam 2 Flashcards
Genetic drift occurs when..
Random or chance events determine which alleles are passed to the next generation
What is a problem of small sample size?
Genetic drift
Genetic drift has four effects on small populations:
- causes allele frequencies to fluctuate at random
- reduces genetic variation
- frequency of harmful alleles can increase
- differences between separate populations can increase -> genetically “drift” apart
All by chance
Fixation
When an allele reaches 100% frequency or disappears completely
Loss of ___ ___ reduces ability of population to respond to changing environmental conditions.
Genetic variation
Increase of ___ ___ can reduce survival and reproduction.
Harmful alleles
Genetic or population bottleneck -
Population may experience sharp reduction in population size
___ may also decrease genetic diversity and spread deleterious alleles.
Inbreeding
Founder effect -
When only a small number of individuals migrate or are otherwise isolated from parent population
Gene flow -
Occurs when alleles are transferred from one population to another via migration or gamete dispersal
Migration -
Movement of individuals
Gamete dispersal -
Movement of gametes
Gene flow has two effects:
- separate populations become more similar
- new alleles can be introduced into population from outside
___ ___ is the only evolutionary mechanism that consistently causes adaptive evolution.
Natural selection
___ are features of organisms that improve their ability to survive and reproduce in their environments.
Adaptations
Micro evolution -
Evolution on small scale on relatively short timeframe
Is natural selection a random process?
No
By consistently favoring individuals with certain alleles, natural selection causes ___ ___.
Adaptive evolution
Clines -
Gradual changes in a characteristic over a geographic region
Phenotypic plasticity -
One genotype produces different phenotypes in different environments
___ ___ can limit how well populations adapt to their environment.
Gene flow
Gene dilution -
Introduce alleles that are not adapted to local conditions
Natural selection does not result in..
A perfect match between organisms and their environment
Constraints on evolution:
- lack of genetic variation
- evolutionary history
- ecological trade-offs
___ does not drive mutation.
Need
Example of constraint from lacking the right genetic variation
Initially, mosquito population lacked alleles that provided resistance to pesticides, so the pesticides were effective
Example of constraint from evolutionary history
Dolphins evolved from terrestrial animals
They have lungs and cannot breathe underwater
What are the creative processes in evolution?
Brings about great chances by modifying traits that are already present, not by creating advantageous traits
Selection is more of an “editing” process than a “creative” process
Adaptations represent ___ in abilities of organisms to perform different and sometimes conflicting functions.
Compromises
Example of constraint from ecological trade-offs
Trade-off between survival and reproduction in female red deer
Adaptive evolution highlights connection between ___ and ___.
Ecology and evolution
Long-term patterns of evolution are shaped by large-scale processes such as..
- speciation
- mass extinction
- adaptive radiation
Species -
Groups of organisms whose members have similar characteristics and can interbreed
Speciation -
Process by which one species diverges into two or more species
Speciation most commonly occurs when a ___ prevents gene flow between two or more populations of a species.
Barrier
Key step in speciation is evolution of ___ ___ that prevent breeding with parental species.
Reproductive barriers
Pre-zygotic -
Prevents mating or fertilization
Post-zygotic -
occurs when population accumulates so many genetic differences that they cannot produce viable, fertile offspring if they mate with parental species
Examples of pre-zygotic reproductive barriers -
- geographic isolation
- ecological isolation
- behavioral isolation
- temporal isolation
- mechanical isolation
- prevention of gamete fusion
Examples of post-zygotic reproductive barriers -
- hybrid embryos do not develop properly
- hybrid adults do not survive in nature
- hybrid adults are sterile or have reduced fertility
Geographic isolation -
Species occur in different places
Ecological isolation -
Species utilize different resources in the habitat
Fruit flies grown on different food sources
Behavioral isolation -
Species have different mating rituals
Fruit flies get separated by lava, each evolve their own mating beats -> wings, stomping feet, rubbing of legs
Females will recognize beats of their species
Temporal isolation -
Mating or flowering occur during different seasons or at different times of the day
Coral
Mechanical isolation -
Structural differences prevent mating or pollen transfer
Duck penis is twirled so only fits in certain duck vaginas
Evolutionary tree -
Branching diagram that represents the evolutionary history of a group
The closest living relatives of pinnepeds are the ___ family.
Weasel
Macroevolution -
Change over a large scale
The first organisms were ___
Prokaryotes
The oldest multicellular fossils are ___ years old.
2.1 billion
Red algae
Animals first appeared how long ago?
600 million years
A variety of fossils illustrate ___ ___ in the origin of tetrapods from fishes.
Transitional steps
Fossil record documents ___ mass extinction events.
Five
Increases in diversity over a relatively short time period are called __ __.
Adaptive radiations
Finches of the Galápagos Islands
Soft-bodied animals predominant in the ___.
Precambrian
Hard-bodied animals appeared during the ___ ___.
Cambrian explosion
“Arms race” between predators and prey
- early predators equipped with adaptations for capturing large prey provided powerful selection pressure that favored heavily armored prey species
- that armor, in turn, promoted further increases in the effectiveness of the predators
Coevolution -
reciprocal evolutionary change in interacting species
Rise of a new species in one group can lead to increased diversity of other groups
Example :
When apples were introduced into North America
Some apple maggot fly populations switched from eating Hawthorn to apple
Probably forming a new species
___ ___ leaves spatially isolated patches that can affect evolutionary processes.
Habitat fragmentation
Human actions that affect environment can alter the three main mechanisms of evolution:
Natural selection
Genetic drift
Gene flow
Speciation reversal -
Fusing two previously isolated species, and thus reducing biodiversity
