An explanation for gene frequencies, genotype, and phenotype coming into equilibrium within a population as genes are passed from generation to generation in absence of evolutionary forces
;HARDY-WEINBERG EQUILIBRIUM;For it to hold true (never is 100%), we must assume:
Population is infinitely large
Mating is random and occurs in proportion to frequencies of genotpyes within popuation
If a population is in genetic equilibrium, two results may be expected:
1) frequencies of alleles do not change from one generation to the next
2) genotypic frequencies will be in the proportion p2, 2pq, and q2 after one generation and will remain in these frequencies as long as equilibrium is maintained
;;Variation within a population
Seldom constant from one generation to the next.; Results from:
Gene mutation
Nonrandom mating/reproduction
Differential survival of individuals
Fecundity rates
;;Genetic Variation and Population Size
Reduced genetic variation can be due to three factors
Inbreeding
Genetic Drift
Neighborhoods and effective population size
;Genetic Variation and Population Size;Inbreeding
Mating among close relatives
Occurs mostly in social animals
Survivorship declines as inbreeding increases
;Genetic Variation and Population Size;INBREEDING EFFECTS
More inbred, the quicker the variation in a population drops
Juvenile mortality increases in captive/inbred populations
Most pronounced in small populations
Has important ramifications in real world
;Genetic Variation and Population Size;GENETIC DRIFT
Changes in allelic representation by chance alone
Sampling error
All of an individual’s genes will be represented somewhere among its gametes, but not in any two of them
Genetic Variation and Population Size Genetic fixation &Founder’s Principle
Genetic fixation: permanent loss of an allele within a small population (result of genetic drift)
Founder’s principle: small group of colonists from a population establish new population in unfilled habitat
Genetic Variation and Population Size PROBABILITY
Higher in small populations
Likelihood of rare alleles increases in small/isolated populations vs.
large populations
Small populations will lose % of their variation over time
Can be countered by immigration
Genetic Variation and Population Size 50 Rule
Populations under 50 suffer highly from genetic drift
Seems insignificant but is magnified over time
Genetic Variation and Population Size Neighborhoods & effective population size
Large populations have genetic risks if mating takes place in neighborhoods
Some animals only breed within a small distance of birthplaces
Some individuals breed, others don’t
Genetic Variation and Population Size;Neighborhoods ; effective population size;NE = (4NMNf)/(NM+Nf)
NE: Effective population size (breeding individuals)
Vital for conservation projects
NM: Number of breeding males
Nf: Number of breeding females
;SELECTION
Changes in population gene pool over time may be due to selection
;;MODES OF SELECTION;Directional, Stabilizing, Disruptive
Directional: favors one extreme phenotype at the expense of all others
Stabilizing: favors the average expression of an optimum intermediate at the expense of both extremes
Disruptive: favors both extremes, although not necessarily to the same extent, at the expense of the average
;MODES OF SELECTION;Group Selection
Selection operatin on a population as a unit depends upon:
More than 1 group within a large entity (subpopulation within a regional population)
Different frequencies of adaptive alleles in groups
traits will benefit the group at the expense of individual
altruistic
;MODES OF SELECTION;Kin Selection
Selection acting on small groups of closely related individuals
Theoretically increases the average genetic fitness of the group at the expense of some individuals
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Wynne-Edwards
Came up with Group slection
Most groups of individuals purposely control their rate of consumption of resources; and rate of breeding to ensure group would not become extinct
There should be no selfish behavior
Should avoid competition
;Group and Kin Selection Background;Individual Selection
Individuals are selfish and act only in their best interest
Mutation Example:
Bird lays only two eggs, plenty of resources
ensures replacement of parents, prevents explosion
Mutation allows 3 eggs, still plenty of resources
larger broods get same advantage, max # of offspring
;Arguments AGAINST Group Selection;IMMIGRATION;
Selfish individuals can migrate into the area.
Never isolated
Arguments AGAINST Group Selection;INDIVIDUAL SELECTION
For group selection to work, some groups must die out faster than others.
In nature, whole groups don’t die out – individuals do so they would be the more powerful evolutionary force
Arguments AGAINST Group Selection RESOURCE PREDICTION
For group selection to work, individuals must be able to assess and predict future availability of food and the population density within their own habitat.
Little evidence that organisms can.
ALTRUISM
Giving a benefit without any reward or where there may even be a cost
Behaviors include:
Grooming, cooperation, give warning signals
Explained in genes
ALTRUISMCoefficient of relatedness
Each parent gives .5 of their genes
Coefficient of relatedness (r): probability that a parent and offspring share a copy of a particular gene
If an organism can pass on its genes through parental care, it can pass them on by caring for siblings, nieces, nephews, and cousins
ALTRUISMInclusive & Direct Fitness, Kin Selection
Inclusive Fitness: pass on genes by other than direct means
Direct Fitness: genes passed on to children
Kin Selection: selection for a behavior that increases inclusive fitness relative to direct fitness
EVOLUTION
MICROevolution: change in gene frequency in a populationMACROevolution: change at the species level and above
SPECIATIONBiological
A group of actively or potentially interbreeding populations that are reproductively isolated from other such groups
SPECIATIONMorphological
Discrete units to which specific names have been given
System of classification defined by Carl vonLinne
SPECIATIONSibling
Morphologically similar or identical natural populations that are reproductively isolated
SPECIATIONSympatric
Origin of isolating mechanisms within the dispersal area of the offspring of a single cline
Takes place in center of patchy environment
Results in formation of multiple sibling species
SPECIATIONAllopatric
Separation of a widely distributed population by some extrinsic barrier that interrupts gene flow
SPECIATIONParapatric
Evolution of a species as a continuous population in a continuous cline
Differs from founder effect:
1) No spatial isolation is required, 2) level of vagility is low, 3) Reproductive isolating mechanisms arise by selection at same time genetically unique individuals colonize or exploit a new environment
GEOGRAPHIC VARIATION
Significant differences often exist among populations or different geographic regions
Variants reflect the environmental selective forces acting on genotype
CLINE
Continuous variation across a species’ geographic range results from the intergradation of gene pools between local populations
;;CLINE;The result of…
Result of phenotypic response to environmental selective pressures that vary on a gradient;/ continuum
Most prevalent among organisms with continuous ranges over a continental area
Usually associated with an ecological gradient such as temperature, moisture, altitude, light
;;GEOGRAPHIC ISOLATE
A population or group of populations that is prevented by some extrinsic barrier from effecting a free flow of genes with others of the same species
;GEOGRAPHIC ISOLATE;Subspecies
An aggregate of local populations of a species inhabiting a geographic subdivision of the range of a species and differing taxonomically from other populations of the species
;GEOGRAPHIC ISOLATE;Geographic Races
Populations connected by intermediate forms or intergrades, so that it is virtually impossible to separate them
;GEOGRAPHIC ISOLATE;Polymorphism
The occurrence of several distinct forms of a species in the same habitat at the same time
Forms are distinct and the characteristic involved are discontinuous – NO overlap
;SPECIATION;Asexual
Species which may reproduce themselves in some nonsexual manner
Agamospecies
Those which lack true sex reproduction
Reproduce via runners, bulbs, corms
Self-ferilization
;MECHANISMS OF SPECIATION;Polypoidy
Spontaneous generation of new species through alteration of chromosome numbers
;MECHANISMS OF SPECIATION;Autopolypoidy
Formed by doubling the chromosomes in any individual of the species
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;MECHANISMS OF SPECIATION;Allopolyploidy
Formed by doubling the chromosomes of a hybrid individual
;MECHANISMS OF SPECIATION;Adaptive radiation
Direction and degree to which a population diversifies
Influenced by the preadaptability of the species population to a new situation
By selective pressures of climate and competition
By the availability of ecological niches
;MAINTENANCE OF SPECIES;Isolating mechanisms
The means by which species maintain diversity
;MAINTENANCE OF SPECIES;Ecological mechanisms
Include habitat isolation and temporal/seasonal isolation
;MAINTENANCE OF SPECIES;Ethological mechanisms
Differences in courtship and mating behavior
;MAINTENANCE OF SPECIES;Mechanical Isolating mechanisms
Structural differences that make copulation or pollination between closely related species impossible
;MAINTENANCE OF SPECIES;Reduction of Mating Success
Does not prevent waste of gametes but highly effective in preventing crossbreeding
