(1) modern discipline (1930s) that synthesizes Mendelian genetics and Darwin's theory of natural selection, (2) studies gene pools of a collection of individuals, (3) resolved that quantitative characteristics are the result of an interaction of many genes
what did Darwinian thought stress?
(1) quantitative characteristics, (2) variations in gradations, (3) natural selection involves a continuum of traits
what did Mendelian thought stress?
(1) traits exist as discrete units (genes), not a continuum, (2) no gradations of traits
why must natural selection act with genetic variation to produce evolution?
natural selection provides conditions in which certain types of genetic variation are favored over others
total of all alleles present in a population
(1) change in a population's gene pool from one generation to the next, (2) individuals are selected, while populations evolve
argued that if Mendel's theory was correct, recessive traits should disappear from a population altogether, leaving only dominant traits
(1) mathematically demonstrated that in a nonevolving population, the relative frequency of dominant and recessive alleles should not change from generation to generation, (2) demonstrated that Mendel's discrete units could be maintained from generation to generation
came to the same conclusion as Hardy, independently
(1) developed by Hardy and Weinberg, 1908, (2) showed mathematically that Mendelian genetics and Darwinian selection were not mutually exclusive, (3) the sexual shuffling of alleles because of meiosis and random fertilization does not affect the overall allelic composition of a population, (4) according to this theory, in a randomly mating population with no evolution or selection, the relative gene frequency will stay the same from generation to generation, (5) provides a base line for tracking the genetic structure of a population
although Hardy's mathematical solution was a way to explain why dominant genes do not "take over" a population, why is it not realistic?
solution depends on a non-evolving population and in reality all populations are evolving to some extent
when the population is in equilibrium, no matter what the generation level, the allelic frequency remains what percent dominant and recessive?
50% dominant, 50% recessive
p^2 + 2pq + q^2 = 1,
p = frequency of the dominant allele,
p^2 = frequency of the homozygous dominant genotype
q = frequency of the recessive allele,
q^2 = frequency of the homozygous recessive genotype
what are the five criteria for maintaining Hardy-Weinberg equilibrium in a population?
(1) large population size, (2) no gene flow in or out of the population, (3) no mutation, (4) random mating, (5) no natural selection
what happens when any of the five criteria for maintaining Hardy-Weinberg equilibrium are not met?
microevolution occurs, and the Hardy-Weinberg equilibrium is no longer in effect
a change in gene frequency in a population that occurs over a relatively short period of time -- no more than a few generations
by being able to pinpoint factors that will change gene frequencies, what can we make predictions about?
the causes of evolution
why are large populations less likely to undergo genetic drift?
large populations have a higher amount of variation between individuals than small populations
the Hardy-Weinberg equation works to predict genotypes in a population only if what remains constant?
what are the five causes of microevolution?
(1) genetic drift, (2) gene flow, (3) mutations, (4) non-random mating, (5) natural selection
(1) changes in the gene pool (frequency of alleles) of a reduced population due to chance alone, (2) events such as natural disasters, disease, or human interference may cause genetic drift by reducing the size of the population by killing individuals unselectively (at random), (3) the gene frequency of the reduced population will no longer be representative of the original population, (4) may reduce variability as the gene pool loses rare alleles
what two situations can lead to genetic drift?
(1) bottlenecks, (2) founder effect
occurs when the genetic make-up of the small surviving population is no longer representative of the original colony
occurs when the gene pool of a newly formed colony is not representative of the original population
(1) changes in the gene pool because of migration of fertile individuals or gametes, (2) if the gene flow between two populations is extensive, a single genetically homogeneous population will result
(1) changes in an organism's DNA, (2) can create a new allele, and the immediate effect is very small in the gene pool, (3) if the new allele is selected for, however, microevolution can occur
occurs when an individual chooses a mate based on specific criteria, which can result in microevolution
the differential success in the reproduction of different phenotypes resulting from the interaction of organisms with their environment, (2) when selection causes a change in the gene frequency of a population, microevolution occurs
why is natural selection so important in microevolution?
natural selection is the only factor that acts as an adaptive force, influencing which individual characteristics are passed on
describes the change in populations of organisms over Earth's history
why are meaningful mutations very rare?
most genes and therefore most mutations are never expressed
a group of organisms that belong to the same species and live in the same geographic area
the existence of two or more inherited forms of a trait in a population
is present when two or more inherited forms of a trait are maintained in a population at constant frequencies over time
what are the two main sources of variation?
(1) mutation, (2) sexual recombination
(1) the appearance of new gene combinations, (2) recombination can occur during meiosis, either by crossing over or by the formation of new chromosome combinations
what are the three forms of natural selection that causes microevolution?
(1) stabilizing selection, (2) directional selection, (3) diversifying selection
(1) the extremes are selected against, and the average is selected for, (2) example: birth weights of humans
one extreme is selected for, and the opposite extreme is selected against
the extremes are selected for, and the average is selected against
influences evolution by propagating traits deemed favorable by the opposite sex, not necessarily the environment
varieties will be selected for, or against, based on what?
based on their ability for survival in a particular environment at a given moment
what are four reasons why natural selection cannot produce the perfect organism?
(1) evolution is based on history (evolution concerns modification of existing structures, and these modifications are constrained because of the limitations imposed by the existing structure), (2) new organisms are compromised in terms of their phenotypes (certain adaptations, especially anatomical structures, are mutually exclusive), (3) not all evolution is adaptive (genetic drift), (4) selection can only act upon existing alleles
why is "species" hard to define?
it is a population-level phenomenon, and populations are complex and constantly changing
what are five working definitions/concepts of "species"?
(1) biological species concept, (2) morphological species concept, (3) recognition species concept, (4) cohesion species concept, (5) ecological species concept
what do the five definitions/concepts of "species" all share?
share the common theme of genetic isolation
biological species concept
(1) two organisms are in the same species when they can produce fertile, viable offspring in free-ranging conditions, (2) emphasizes reproductive isolation, (3) limitation is that the concept does not work for classifying extinct or asexually reproducing species
morphological species concept
(1) species are classified based upon anatomical differences, (2) most species that have been classified to date have been categorized by this method, especially extinct species or fossil remains of a lineage, (3) limitation is that the concept assumes that morphological differences are the result of substantial genetic differences between individuals
recognition species concept
(1) species are classified based upon their courtship rituals (genetic, morphological, and behavioral) and mate selection, (2) limitation is that the concept does not work for classifying extinct or asexually reproducing species
cohesion species concept
(1) species are classified based upon mechanisms they use to maintain the phenotypic integrity of the population, (2) example: reproductive barriers, (3) advantage is that the concept recognizes the occurrence of fertile hybrids produced by the interbreeding of two different species while acknowledging the integrity of the parent species, (4) limitation is that the concept does not work for classifying extinct species
ecological species concept
(1) species are classified based on their ecological niche, (2) limitation of the concept is that the ecological niche encompasses a vast array of details involving the life history of an organism--some of which may be difficult to observe in nature and may be completely lacking in the fossil record
which usually occurs first, physical isolation or genetic isolation?
usually physical isolation (geographic barriers/isolation) precedes genetic isolation
what are some geographical disturbances that may cause physical isolation?
(1) forest fire, (2) earthquake, (3) formation of a canyon, (4) continental drift
(1) a type of speciation that can occur when a geographical barrier separates a splinter population from the original population
after geographical isolation, what three sequential events may lead to allopatric speciation?
(1) the founder effect, (2) the continuation of genetic drift, (3) selection pressure of the new environment
what allows a population to be genetically homogeneous and thus maintain itself as a single gene pool (species)?
What is it about physical barriers that is important?
it prevents intermating between individuals in the two populations
(1) the formation of a new species from a subpopulation that is physically located within the parent population, (2) major driving force in the evolution of plants, (3) mechanism of sympatric speciation is polyploidy
(1) a chromosomal modification in which the organism has more sets of chromosomes than the typical diploid number (two sets) of chromosomes, (2) caused by nondisjunction in mitosis or meiosis
what are the two major types of polyploidy?
(1) autopolyploidy, (2) allopolyploidy
(1) all chromosomes come from the same species, (2) results when a self-fertilizing individual produces diploid gametes and gives rise to offspring that are tetraploid (having a 4n number of chromosomes), (3) the tetraploids can self-fertilize or mate with other tetraploids, (5) many plants can self-fertilize, including Mimulus guttatus
(1) the chromosomes come from two different species, (2) occurs when two different species interbreed, producing an individual with more than two sets of chromosomes, (3) hybrids are typically sterile, but there are mechanisms that can produce allopolyploid species from hybrids
how often does sympatric speciation occur among animals?
there are very few documented cases of sympatric speciation in animals
what are the two theories that present differing views as to how species arise?
(1) gradualism, (2) punctuated equilibrium
(1) the theory that new species gradually diverge as a result of accumulations of small changes, (2) because of the lack of transition fossils, some dispute this theory, (3) supporters argue that gradual change may not be recorded in the fossil record
the theory that new species develop in periods of rapid change followed by long period of no change
evaluating both gradualism and punctuated equilibrium involve what?
involve estimating the life span of a species and examining the fossil record for evidence of morphological change
what is the average life span of species?
approximately 4-5 million years
what is one possible reason why not many transition fossils have been found?
strata that date back millions and billions of years ago are often very thin layers, and thus reduce the likelihood of finding transition fossils
which theory (gradualism or punctuated equilibrium) do transition fossils found to date appear to support?
the punctuated equilibrium theory
before the 1930s, why did Mendelian geneticists disagreed with Darwinians about evolution?
the Mendelian geneticists did not have any genetic basis for understanding the evolutionary process
what is the estimated amount of time required for morphological and genetic changes to produce a new species?
approximately 50,000 years