06. Evidence for evolution & mechanisms of evolution Flashcards
What is evolution?
Changes in the genetic make-up of populations over time, sometimes resulting in adaptation to the environment and the origin of new species.
-change in allele frequencies over time
What are the lines of evidence for evolution?
- Structural
- Microbiology
- Direct observation
Homology
The existence of shared ancestry between a pair of structures, or genes, in different taxa.
Example: Despite modifications, all mammals
share several traits
-bone structure
Vestigial structures
-genetically determined structures that are
retained despite having lost some or all of their ancestral function
Vestigial structures in humans (4)
- tail bone - makes sense if we had a tail
- arrector pilli muscle - makes sense if we were covered in fur
- wisdom teeth - makes sense if we had poor oral hygiene
- appendix - makes sense if we had to digest cellulose
Principle of faunal succession:
Sedimentary rock strata contain
fossilized organisms that succeed
each other vertically in a specific,
reliable order
Microbiology evidence of evolution
- all life forms have DNA
- DNA is replicated, translated, and transcribed similarly across all life forms
- Genetic similarity across life forms
Sequence homology
-protein or DNA sequences that are similar due to shared ancestry
Direct observation of evolution
- the evidence for evolution is that we can see it taking place around us!
- Example: mosquito population evolved resistance to the pesticide
What are the units of evolutionary change
Genes
Gene pool
all the alleles for all loci in a population
What happens if the allele frequency changes within the gene pool?
evolution has occurred
What is a population?
A localized group of individuals capable of interbreeding
and producing fertile offspring
What is a prerequisite of evolution?
Variation in heritable traits
Genetic variation
differences in genes or other DNA segments
Sources of genetic variation
- Mutation
2. Recombination
Mutatations
- number one source of all new variation
- mutations can be neutral, deleterious, advantageous
Recombination
the shuffling of existing alleles as a result of sexual reproduction
The Hardy-Weinberg Equation
p^2 + 2pq + q^2 = 1
-Describes the genetic makeup we expect for a population that is not evolving
at a particular locus
-if the population meets HW expectations it is said to be in “HW equilibrium”, otherwise it may not be evolving
What are the 5 conditions a population must meet to be considered in H.W. equilibrium?
- No differences in the survival & reproductive success of individuals
- No movement of individuals into and out of the population
- No mutation
- Population must be large enough to prevent sampling errors
- All mating must be random
What are processes that can change allele frequencies?
- Natural selection
- Genetic drift
- Gene flow
- Mutation
Natural selection is an inescapable conclusion if a population has…
- Variation in traits
- relationship b/w traits and survival and/or reproduction
- Variation can be inherited
How does natural selection involve both chance and sorting?
chance - new genetic variations arise by chance
sorting - beneficial alleles are “sorted” and favored by natural selection
Directional selection
Favors individuals at one extreme end of the phenotypic range
Disruptive selection
Favors individuals a both extremes of the phenotypic range
Stabilizing selection
favors intermediate variants and acts against extreme phenotypes
Sexual selection
- selection for mating success
- can result in sexual dimorphism
Intrasexual selection
-direct competition among individuals of one sex (often males) for mates of the opposite sex
Intersexual selection
-occurs when individuals of one sex (usually females) are choosy in selecting their mates
Genetic drift
A change in the frequency of an allele due to the random effects of finite population size.
- strongest when populations are small
- does not lead to adaptive evolution
Bottleneck effect
Rapid reductions in population size associated with external
pressures on a population
Founder effect
Occurs when a small number of colonizing individuals “founds” a new population in a new area
Gene flow
- movement of alleles among populations
- tends to reduce variation over time
