exam 2 semester 2

evolution

Heritable change in one or more characteristics of a population from one generation to the next

microevolution

change in a single gene in a population over time

macroevolution

relates to formation of new species or groups of related species

species

group of related organisms that share a distinctive form, and can interbreed and produce offspring

darwin definition of evolution

species are descendants of ancestral species that were different from those alive today, change in genetic populations over time

mantises illustrate three key observations about live

organisms are adapted for life in their environments, the many shared characteristics of life, the diversity of life

how is evolution viewed as a pattern

revealed by scientific data showing that life has evolved over time

how is evolution viewed as a process

consists of the mechanisms that cause the pattern of change

Origin of Species

1859, charles darwin, started the era of evolutionary biology

aristotle and species

believed that they were fixed, arranged species on the scala naturae

1700s and speciation

scientists interpreted adaptations as evidence of design by a Creator

carolus linnaeus

developed nested classification system and binomial formation

fossils

remains or traces of organisms from the past mineralized in sedimentary rock

strata

layers of sediment

paleontology and georges cuvier

observed that older strata contained fossils less similar to current species, new species appear and disappear, boundaries between strata were major events

james hutton

earths geologic features were formed gradually

charles lyell

the same geologic processes operate today as in the past

jean baptiste de lamarck hypothesis of evolution

based on fossil invertebrates and living species, proposed tow principles

jean baptiste lamarck prinicples

use and disuse (used body parts are strong, unused are weak), inheritance of acquired characteristics (modifications can be passed to offspring)

charles darwin 1831

hms beagle voyage, he collected specimen in south africa

galapagos islands and darwin

found that similar but different species of finches were found on multiple islands

adaptations

inherited characteristics that could enhance an organisms survival and reproduction in specific environments

natural selection

process in which individuals with certain inherited traits tend to survive and reproduce at high rates because of those traits

descent with modification by natural selection explains three broad observations

unity of life, diversity of life, ways organisms are suited to life

tree of history of life

labeled branches are present day, unlabeled branches are extinct

artifical selection

modification of species by humans, breeding individuals with desired traits

members of a population and traits

vary greatly in their inherited traits

species and offspring

capable of producing more offspring than the environment can support, many will not survive

traits influence

survival and reproduction, will lead to the trait becoming more prevalent

four types of data document the pattern of evolution

direct observations, homology, the fossil record, biogeography

two examples of direct observations of evolutionary change

natural selection in response to introduced species, evolution of drug-resistant bacteria

how does methicillin work

inhibits an enzyme used by bacteria to produce cell walls, resistant strains use different protein to produce cell walls

natural selection does not

create new traits, selects for favorable traits already present

evolution by natural selection can occur

rapidly

homologous structures

anatomical resemblances that represent variations on a structural theme present in a common ancestor

all vertebrate embryos have a

post anal tail and pharyngeal arches, and these arches develop into structures with very different functions

vestigal structures

remnants of features that served a function in the organisms ancestors

convergent evolution

independent evolution of similar features, forms analogous features (similar in disntaly related groups)

fossil records and evidence of evolution

documents patterns of evolution, past organisms are different from present day

fossils can document

important transitions in evolution

continental drift and evolution

helps predict where and when different species evolved

why is darwins theory a theory?

integrates diverse areas of biological study and stimulates many new research questions

natural selection acts on

indviduals, but only populations evolve

population

group of individuals of the same species that occupy the same environment at the same time

population genetics studies

genetic variations of the gene pool (all alleles for every gene in a given population) and how these variations change

three mechanisms cause allele frequency chage

natural selection, genetic drift, gene flow

genetic variation

differences in genes or other DNA sequences among individuals

individuals in a species vary in

phenotype, caused by inherited genotype and environmental influences

discrete characters

determined by a single gene, either or basis

quantitative characters

determined by two or more genes, polygenic inheritence

genetic variation two levels

gene and moleuclar variablitiy

gene variability

whole gene level, measured by average heterozygosity, can result in changes due to natural selection

molecular variability

molecular level, compares the nucleotide sequences of two or more individuals

nucleotide variability rarely results in

phenotypic variation, as it usually occurs in introns

phenotypic variation can result from

environmental influences and genetic differences, but only the genetically determined part can cause evolution

genetic variation originates

when new genes arise by mutation, gene duplication, these variations are produced rapidly

mutation

change in the nucleotide sequence of dna, caused by replication errors or expose

point mutation

change in a single nucleotide, significant impact on phenotype

heterozygote protection

maintains a pool of alleles that could be beneficial if the environment changes

neutral variation

variation with no selective advantage or disadvantage

if duplicated genes persist

mutations can accumulate and new functions may arise

new combinations of existing alleles can occur through three mechanisms

crossing over, independent assortment, fertilization

populations can only evolve if

individuals differ genetically, one of the factors that causes evolution must be at work

a locus is fixed if

all individuals in a population are homozygous for the same allele

if there are two or more alleles for a locus

individuals may be homozygous or heterozygous

allele frequencies for diploid organisms

the total number of alleles at a locus is the total number of indivdiuals times two

harvey weinberg equation

describes relationship between allele and genotype frequencies when a population is not evolving

hardy weinberg equations

p+q = 1, p2 + 2pq + q2 = 1

hardy weinberg principle

describes the expected genetic makeup for a population that is not evolving at aparticular locus

conditions for harvey weinberg equillibrium

no mutations, random mating, no natural selection, large population, no gene flow

natural selection

based on differential success in survival and reproduction

natural selection can cause

adaptive evolution, aprocess in which traits that enhance survival or reproduction increase in frequency over time

genetic drift

process in which chance events cause allele frequencies to fluctuate unpredictably from one generation to the next

genetic drift tends to

reduce genetic variation through the random loss of alleles

two explanations for genetic drift

founder and bottleneck effect

founder effect

few individuals are isolated, allele frequencies in the smaller founder population are different than the original population

bottleneck effect

when there is a drastic reduction in population size, the gene pool is now different than the original gene pool

gene flow

consists of the movements of alleles among populations, tends to reduce variation among populations over time

only natural selection

consistently increases the frequencies of alleles that provide reproductive advantage

relative fitness

the contribution an individual makes to the gene pool of the next generation relative to the contributions of others

three ways natural selection can alter the frequency distribution of heritable traits

directional, disruptive, and stabilizing selection

directional selection

caused by environmental change or migration, favors individuals at one extreme end of the phenotypic range

stabilizing selection

favors intermediate variants and acts against extreme phenotypes

disruptive selection

favors individuals at both extremes of the phenotypic range

sexual selection

process in which individuals with certain heritable traits are more likely to obtain mates than other individuals of the same sex

sexual dimorphism

difference in secondary sexual characteristics between the sexes

intrasexual selection

direct competition among individuals of one sex for mates

intersexual selection or mate choice

occurs when individuals of one sex are choosy in selecting their mates

balancing selection

when 2 or more phenotypic forms are maintained in a population, natural selection does not favor one phenotype over another

mechanisms that lead to balancing selection

frequency dependent, heterozygote

fitness of a phenotype depends on

how common it is, produces balanced polymorphism

positive frequency dependent selection

occurs when the more common variant is in a popualtion

negative frequency dependent selection

less common variant in a population, higher fitness

heterozygote advantage

occurs when heterozygotes have a higher fitness than both kinds of homogyotes

why can natural selection not fashion perfect organisms

selection can act only on existing variations, evolution is limited by historical constraints, adaptations are often compromises

speciation

process by which one species splits into two, produced diversity of life

this confirms that morphologically distinct species are discrete groups

comparisons of physiology, biochemistry, and DNA sequence

biological species concept

species is a group of populations whose members can interbreed in nature, produce fertile offspring, and can not do the same with other groups

hybrids

offspring that result from interspecific mating

three ways that prezygotic barriers block fertilization

impedes mating attempts, prevents successful mating attempts, hinders fertilization if mating is successful