Bio 2 Evolution

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Biological Species concept

Proposed by Ernst Mayr
Most widely used and taught concept
Important points
A species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations.
Gene flow between populations holds the phenotype of a population together

problems with biological species concept

Tions and Ligers and Grolar Bears!?
1/3 of known mammalian hybrids are fertile
Science (02.11.05) - Trent Holliday
Self-pollinating plants
Breeding criteria is impractical in many cases
Asexual species
Fossils

Morphological Species concept

a classification system based on observable and measurable phenotypic traits

morphology

the branch of biology that deals with the structure of animals and plants

Phylospecies

terminal node in a cladogram (phylogenetic tree)

ecological species concept

views a species in terms of its ecological niche
It applies to sexual and asexual species and emphasizes the role of disruptive selection

Microevolution

leads to subspecific differences
Change in frequency of alleles
Antibiotic Resistance

Sympatric speciation

occurs as individuals from the two evolving species are in contact with one another

Allopatric speciation

occurs as individuals are physically separated somehow

reproductive isolation

separation of species or populations so that they cannot interbreed and produce fertile offspring

Sympatric Speciation

Disruptive selection may lead to sympatric speciation
Hybridization can lead to sympatric speciation

Polyploids

individual organisms that have more than two chromosome sets

High Speciation rates

species from large taxa (rich get richer)
species with low dispersal rates
species with specialized diets
animals influenced by sexual selection
plant species that are animal-pollinated vs. wind-pollinated

speciation

The process by which a new species evolves from a prior species, the most basic process in macroevolution.

Directional selection

form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve

Disruptive selection

form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle

stabilizing selection

form of natural selection by which the center of the curve remains in its current position; occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end

Natural Selection

The nonrandom and differential reproduction for different genotypes

Fitness

contribution of a phenotype to the genetic composition of subsequent

Mechanisms of Evolution

Mutations
Gene Flow
Genetic Drift
Nonrandom Mating
Natural Selection

bottle-necking effect

Something knocks out many alleles leaving only a few for the population to repopulate

Founder effect

change in allele frequencies as a result of the migration of a small subgroup of a population

Genetic drift

The gradual changes in gene frequencies in a population due to random events

Gene flow

the transfer of alleles into and out of the population due to the movement of fertile individuals or their gametes

Nonrandom

Nonrandom mating occurs when the probability that two individuals in a population will mate is not the same for all possible pairs of individuals.
E.g. Homozygous recessives choose other homozygous recessive
Often falls into category of natural selection

Descriptive Evidence for Evolution

Fossil Record
Homologous Structures
Developmental Similarities
Vestigial Structures
Biogeography - Galapagos and South America
Molecular Record

Homology

similarity between two structures due to inheritance from a common ancestor

Analogy

resemblance in function and/or appearance that is due to convergent evolution, not common descent

evolution

Biological definition- any genetic or the resulting phenotypic change in organisms from generation to generation

Evolution

A change in allele frequencies in a population over time

A population

the smallest unit that can evolve

Adaptation

the process by which adaptive traits evolve, traits that enhance the survival and reproductive success of their bearers and to the characteristics themselves

natural selection

the non-random and differential reproduction for different genotypes

Uniformitarianism

the mechanisms of change are constant over time, the same geologic processes that operated in the past are still operating today and at the same rate. example: grand canyon has always been there

gradualism

the slow changes over time. example: erosion caused the creation of the grand canyon

types of evidence used to explain the theory of evolution

fossil record, homologous structures, developmental similarities, vesigial structures, biogeography, molecular record

fossil record

the fossil evidence that we have that allows us to trace various species

homologous structures

structures in different species that are similar because of common ancestry

vestigial structures

a feature of an organism that is a historical remnant of a structure that served a function in the organism's ancestors

biogeography

the study of the past and present geographic distribution of a species

molecular record

suggests that a series of evolutionary changes is tied to a progressive accumulation of alterations in the DNA sequences

homology

the similarity between two structures due to inheritance from a common ancestor

anology

resemblance in function and/or appearance that is due to convergent evolution NOT common decent

five assumptions of Hardy-Weinberg Equilibrium

random mating, large population size, no migration between populations, no mutations, natural selection does not affect the alleles under consideration

Hardy-Weinberg meaning

The population would NOT be evolving

required for a population to evolve

mutations that lead to evolutionary growth

mechanisms of evolutionary change

mutations, gene flow, genetic drift, non random mating, natural selection

mutations

a change in the Nucleotide sequence of an organism's DNA

gene flow

the transfer of alleles from one population to another, resulting from the movement of fertile individuals or their gametes

genetic drift

a process in which chance events cause unpredictable fluctuations in allele frequencies from one generation to the next. the effects are most pronounced in small populations

non random mating

occurs when the probability that two individuals in a population will mate is not the same for all possible pairs of individuals

natural selection

a process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits

bottleneck effect

a random occurrence that causes a struggle in the survival of a population. example: weed killer

fitness

describes the ability to both survive and reproduce, and is equal to the average contribution to the gene pool of the next generation that is made by an average individual of the specified genotype or phenotype

mechanisms of genetic variation

mutations, genetic variation, sexual recombination/diploidy, balancing selection

diploidy

the state of being a diploid cell

evolutionary constraints

selection can only exist on existing variation, historical/developmental processes, trade-offs

convergent evolution

the evolution of similar features in independent evolutionary lineages

writing scientific names

italicized Genus=capitalized, then species

Biological Species Concept

says that a species is a group of populations whose members have the potential to interbreed nn nature and produce viable, fertile offspring, they do not breed successfully with other populations

however: gene flow between populations holds the phenotype of a population together and 1/3 of known mammalian hybrids are fertile

however: gene flow between populations holds the phenotype of a population together and 1/3 of known mammalian hybrids are fertile

phylospecies concept

based on having a common evolutionary history and/or ancestor

Habitat Isolation

populations live in different habitats and do not meet

Behavioral Isolation

little or no sexual attraction between males and females

Temporal Isolation

mating or flowering occurs at different seasons or times of the day

Mechanical isolation

structural differences in genitalia or flowers prevent co-population or pollen transfer

gametic isolation

- male and female gametes fail to attract each other or are inviable

reduced hybrid viability

hybrid zygotes fail to develop or fail to reach sexual maturity

reduced hybrid fertility

hybrids fail to produce functional gametes

reduced hybrid fertility

offspring of hybrids have reduced viability or fertility

microevolution

leads to subspeific differences, changes in frequencies of alleles, antibiotic resistence

macroevolution

speciation

speciation

an evolutionary process in which one species splits into two or more species

allopatric speciation

occurs when species become physically separated (this is the most common)

sympatric speciation

occurs as individuals from the two evolving species are in contact with one another

mechanisms of speciation

natural selection, genetic drift, mutation, hybridization, polyploidy

hybridization

in genetics, the mating, or crossing of two true-breeding varieties

polyploidy

a chromosomal alteration in which the organism possesses more than two complete chromosome sets. it is the result of an accident in cell division

divergence

it is the pattern that evolution most often takes when new species evolve

the tree of life

goal is to find phylogeny of all living things, produced in the 3 domain system

synapomorphy

The possession by two organisms of a characteristic (not necessarily the same in each) that is derived from one characteristic in an organism from which they both evolved

node in phylogenetic tree

a hypothesis of the evolutionary history of a species or groups of related species

homoplasy

a structure formed through convergent evolution, phylogenetic trees does not represent convergent evolution well

monophyletic

one single ancestor

polyphyletic

group has multiple ancestors

paraphyletic

group includes only some of the descendants from an ancestor

parsimony

the simpest answer is likely to be correct

scientific explanations

must be testable and rejectable

natural selection acts

directly on the phenotype and indirectly on the genotype

race

a person's appearance, determined biologically with genetic traits

ancestry

the evolutionary or genetic line of descent of an animal or plant

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