module 5 Flashcards
1835
Charles Darwin visited the Galapagos Islands and became convinced various populations evolved from ancestral form.
1838
After reading an essay by Thomas Malthus, he theorized some individuals would have a competitive advantage conferred by favorable characteristics.
Expression and Environment
because environmental condition show continious _____
changes in conditions can cause the _____ produced by a given ____ to ______
- Environmental conditions can show continuous variation:
- temp
- precipitation
- sunlight
- predation level
Changes in conditions can cause the phenotype produced by a given genotype to vary continuously
Phenotypic plasticity
Ability of one genotype to give rise to different phenotypes under different environmental conditions
Norm of reaction
smaller norm of reaction
-larger norm of reaction
- Set of phenotypes expressed by a single genotype across a range of environmental conditions
- leads to an increase in fitness under current environmental conditions
- smaller norms of reaction-continuous - less affect to phenotype-lower fitness
- larger norms of reaction-more of a slope-bigger change in phenotype-higher fitness
Developmental plasticity
phenotypic changes cannot be reversed.-adjust to the conditions of when they were born, do not adjust again later in life
Low light vs. high light conditions
Acclimation
- -Phenotypic plasticity in response to current environmental conditions that is reversible
- Seasonal changes in temperature tolerance in fish
- Upper and lower limits to temperatures they can tolerate
- Limits change as water temperature changes with the seasons
A species is rarely composed of a single, continuous interbreeding population
- Usually a group of subpopulations
- –Local populations of interbreeding individuals
- –Linked by movement of individuals
Genetic variation can be found
- within subpopulations-gene pools
- among subpopulations = genetic differentiation within that larger population
what is a Gene pool and what are the two ways it is measured
-sum of all genetic information (all alleles) across all individuals in a population
Usually measured in two ways
-allele frequency
-genotype frequency
Phenotypic evolution
result of changes in
- Change in mean or variance of phenotype of a trait across generations
- Result of changes in allele frequencies
- -From differences in fitness among genotypes
Natural selection acts directly on
directly on the phenotype
Peter Grant and Rosemary Grant
- Studied finches on the Galapagos Islands for over 20 years
- Observed and documented a shift in physical characteristics during a period of extreme climate change
- Variation exists in beak size in Darwin’s medium ground finch (Geospiza fortis)
- This characteristic has high heritability
Stabilizing Selection
- Acts to impede changes in a population by:
- Acting against extreme phenotypes
- Favoring average phenotypes.
Directional Selection
- Leads to changes in phenotypes by
- Favoring an extreme phenotype over other phenotypes in the population.
Disruptive Selection
- Creates bimodal distributions by:
- Favoring two or more extreme phenotypes over the average phenotype in a population.
Hardy Weinberg principle states that:
In a population mating at random in the absence of evolutionary forces, allele frequencies will remain constant.
Hardy Weinberg Conditions
- Random Mating
- No Mutations
- Large Population Size
- No Immigration
- Equitable Fitness Between All Genotypes
Likely, at least one of these conditions will not be met and allele frequencies will change.
Potential for evolutionary change in natural populations is very great.
-potential for evolution is great
Hardy-weinberg requires what in mating:
Equal participation in mating
Lack of consistent choice in mating-random mating
Sexual Selection
occurs when
-Occurs when mates chosen non-randomly
-Certain individuals have greater chance of obtaining mate
May be based on:
-Perceived Quality
-May or may not indicate fitness
Proximity
-Inbreeding
Assortative Mating
choose mates based on their
Individuals in choose mates based on their phenotype
-Reflects their genotype
If mating is random
Chance that an individual mates with another individual is equal to
Chance that an individual mates with another individual is equal to the frequency of the genotype of that individual in the population
Nonrandom mating changes genotype frequencies but
does not (usually) change allele frequencies
Different types of assortative mating include:
Positive
-Mates are phenotypically more similar than expected by chance;
–Increases the frequency of homozygotes
Common
-In many cases is related to timing of reproduction
–Flowering time in plants
Negative
-Mates are phenotypically less similar than expected by chance
-Increases the frequency of heterozygotes
Inbreeding
increases
can lead to
- Individuals mate with other members of the population who are more closely related to them than expected by random chance
- –Increases homozygosity at all genes
- Can lead to inbreeding depression
- -Offspring are more likely to be homozygous for harmful recessive alleles
- -Can lead to reductions in fertility, vigor, fitness and even death
Small populations have
genetic drift
Genetic drift
Random processes (event) can change gene frequencies
Habitat Fragmentation
- Reduces habitat availability & Connectedness
- -Separates Populations
- -Decrease Local Pop. Size -> Isolated Gene Pools
- Genetic drift reduces genetic diversity within natural populations.
what kind of correlation is between population size and genetic diversity
-Found significant positive correlation between
Population size and genetic diversity
Picea chihuahuana
Restricted to peaks of Sierra Madre Occidental in N. Mexico
Ledig et.al.
Examined populations to determine if the species has lost genetic diversity
As consequence of reduced population size.
Immigration
- high rates
- low rates
-Most populations Open.
–Individuals move between sub-populations
–Rate of interchange important.
–High rates ->common gene pool
—Less likely to cause change
—-Sub-pop Gene Pools Similar
Low rates ->genetic divergence
Immigrants likely to enter with different allelic frequencies
Leads to Evolution
Natural Selection Differential Survival & Reproduction some individuals produce\_\_\_\_\_ due to \_\_\_\_ offspring \_\_\_\_ to reproduce
natural selection can:
____
conserve what
Some individuals produce more offspring
Due to Phenotypic Characteristics & Environment
Offspring live to reproduce
Natural selection can:
Disfavor, favor
Conserve the genetic make-up of a population.
Hardy-Weinberg Violations Lead to Evolutionary Change
-Mechanisms of Evolution If H-W Violated : No Mutations -> Mutation No Immigration -> Gene Flow Large Population Size -> Genetic Drift Random Mating -> Sexual Selection Equitable Fitness-> Natural Selection
Natural selection
-changes what frerquencies
can result in ____ to environment
depends on ____ of trait
- Changes genotypic and phenotypic frequencies in populations
- Can result in adaptation to the environment.
- Depends on heritability of trait.
h2 = VG / VP
VG : Genetic variance
VP: Phenotypic variance
h2=natural selection
Variation in Plant Populations
distinctive ____
genetically distinct ____
- Many plant species differ dramatically in form along a Cline
- –From one elevation to another.
Clausen et.al. found evidence of adaptation by ecotypes to local environmental conditions in Potentilla glandulosa.
- –Distinctive ecotypes.
- —-Genetically distinct geographic varieties
In general, genetic variation is lower in:
Isolated island populations
Smaller island populations
Genetic Drift & Bottlenecks Greater
Reduced genetic variation indicates a ______ potential to evolve
Reduced genetic variation indicates a lower potential for a population to evolve.
Environments are dynamic
Natural selection favors different phenotypes under
the fitness of a particular phenotype varies depending on the
- Natural selection favors different phenotypes under different environmental conditions
- –the fitness of a particular phenotype varies depending on the environment
- Fitness limitations of a phenotype under different environmental conditions are the result of trade-offs imposed by constraints
Morphology and diet
represent a trade-off that constrains the evolution of adaptations
Finches provide examples of evolution occurring at three levels of organization
within a population
among subpopulations within a species
among species
adaptive radiation
-multiple species within a single lineage that exploit different features of the environment
Darwins theory of natural selection
- organisms begat like organisms
- chance variation between individuals -some are heritable
- more offspring are produced each generation than can survive
- some individuals because of physical or behavioral traits, have a higher chance o surviving than others in the same popoulation- traits more favorable than others
What is Evolution?
Any kind of change in heritable traits within a population across generations.
Development of Theory of Natural Selection (Darwin & Malthus) -
Darwin’s theory of natural selection stretches Malthus’s principle beyond the boundaries of the human population and political economy. Darwinian theory of natural selection made the connection between organisms and their environments stronger than they had ever
Mendelian genetics
Augustinian Monk Studied garden pea (Pisum sativum). Discovered characteristics pass from parent to offspring in form of discrete packets called genes. Exist in alternate forms - alleles. Some prevent expression of others.
