Ch. 8 Evolution Flashcards
(24 cards)
Microevolution
a generation to generation change in the frequencies of alleles within a population
Allele
alternative forms of the same gene
Gene pool
all the alleles, in all individuals, that make up a population
Sources of Variation: Mutations
→ change in DNA sequence that may have no effects, harm or help fitness
Sources of Variation: Sexual reproduction
→ meiosis scrambles existing alleles
Non random mechanisms of microevolution (3 types of selective pressures)
Natural selection
Directional
→ individuals at one end on the phenotype range have higher fitness
Stabilizing
→ individuals near the center of the phenotype range have a higher fitness (ie. lots of babies)
Disruptive
→ individuals at the upper and lower ends of the [phenotypic range have higher fitness;
may lead to 2 distinct phenotypes
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Pesticide Resistance
→ first time spraying kills 99%, but subsequential sprayings are less effective
→ directional selection (towards resistant pests)
Antibiotic resistance
→ directional selection
Sexual selection
→ individuals with certain inherited traits are more likely to obtain mates than others
Artificial selection
→ humans intentionally breeding plants/animals to produce certain traits (not random)
Random mechanics of microevolution: Genetic Drift
→ change in gene pool due to chance
→ impacts smaller populations
Bottleneck effect
→ population size is reduced therefore gene pool is reduced
→ by chance some alleles will be more frequent than others
→ decreases genetic variation in population (ie. natural disasters)
The founder effect
→ The loss of genetic variation when a new population is established by a very small number of individuals from a larger population
→ The smaller the colony, the less genetic variability
Gene flow
→ involves the random exchanges of genes with another population
→ reduces genetic differences between populations
What is a species
→ biological species concept
Species
a group that have the ability to breed with one another in nature, and produce fertile offspring
Speciation
the process of forming a new species
Microevolution
Small evolutionary changes (ie. allele frequency changes) that result in phenotypic changes of a species
How populations evolve
Macroevolution
Dramatic (large scale) evolutionary changes these include:
Evolution of new major features (ie. wings or venom)
Origin of new species
Extinction of species
Hybrid
an offspring that results from the mating of individuals from 2 different species
→ often infertile (ex. horse + donkey = mule)
Adaptive Radiation
→ new species evolve from common ancestors through genetic drift and adaptation
→ Also known as, divergent evolution, because it leads to the diversification of life
→ organisms arriving in new habitats must adapt to new/unique environments - causing diversification of species
Ie. islands often have species found nowhere else
Convergent evolution
→ distantly-related species that live in similar environments, develop similar adaptations
Ie. sharks, dolphins, and penguins have similarities, but have actually evolved convergently to resemble each other
Convergent evolution produces
Structures (features perform similar function but have evolved completely separately)
The rate of specification (2 types)
Gradualism: evolution by gradual accumulation of small genetic changes over long period of time
Punctuated equilibrium: sudden changes to a species
→ opposite of gradualism
→ theory proposed by paleontologists N. Eldredge and J. Gould
