Untitled Flashcards Set

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Evolution on populations 

Biogeography - the study of the geographic distribution of species, provides support for evolution 

Microevolution - the change in allele frequencies in a population over generations, this is evolution at its smallest scale 

Gene pool - all copies of every allele at every locus with all members of a population 

Mutations 

• Most mutations are neutral or have negative effects, occasionally the consequences are beneficial  

• Point mutation is a change in a single base pair in DNA 

• Chromosomal level mutations are a change in the number or composition of chromosomes

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Evolutions of populations 

Natural selection 

• Variation exists ang individual organisms that make up a population 

• Some of the trait differences are heritable 

• Survival and reproductive success are highly variable 

• Subset if individuals that survive best and produce the most offspring is not a random sample of the population 

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Microevolutionary forces 

Natural selection 4 postulates

• Variation exists and individual organisms that make up a population 

• Some of the trait differences are heritable 

• Survival and reproductive success are highly variable 

• Subset if individuals that survive best and produce the most offspring is not a random sample of the population  

Genetic drift 

• The smaller the sample the greater the chance of random deviation from a predicted result 

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

• Genetic drift tends to reduce genetics variation through the random loss of alleles  

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Genetic drift - chance events cause unpredictable fluctuations in allele frequencies from one generation to the next 

Founder effect 

• Occurs when a few individuals become isolated from a larger population 

• Allele frequencies in the smaller founder population are different from those in the parent population 

• ex) genetic drift could occur if a few individuals are indiscriminately blown to a new island by a storm 

• New population established by small group 

Bottleneck effect 

• Occurs when there is a drastic reduction in population size due to a sudden change in the environment 

• The resulting gene pool may no longer be reflective of the original populations gene pool 

• If the population is small it may be  further affected by genetic drift 

• Loss of significant proportion of original population 

Gene flow 

• Consists of movement of alleles among populations 

• Allele can be transferred through the movement of fertile individuals or gametes ex) pollen 

• Tends to make populations more similar to each other over time  

Speciation - forms a conceptual bridge between the processes of microevolution and macroevolution 

• Microevolution - consists of  hinges in allele frequency in a population over time 

• Macroevolution - refers to broad patterns of evolutionary change above the species level 

Speciation is a splitting event that results from a two step process 

• Genetic isolation, barrier to gene flow isolated populations  

• Genetic divergence, mutation, selection and genetic drift in isolated population cause divergence 

Species concepts 

Species - evolutionary independent population or group of populations 

The biological species concept 

• Reproductive isolation, results in lack of gene flow between populations 

• Members of populations do not interbreed to fail to produce viable, fertile offspring after mating  

The morphological species concept 

• Individual lineages differ in size shape or other morphological features 

• Distinguishing features most likely arise if populations are independent and isolated from gene flow 

• Usbale for fossils and living organisms 

• Can be subjective 

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Monophyletic group -  consists of an ancestral population plus all of its descendants also called  clade or lineage 

• Identifies by synapomorphies 

• Synapomorphies - homologous traits found in a common ancestor and all the descendants but missing from more distantly related groups ex) white fur distinguishes polar bears in a monophyletic group of bears  

Prezygotic barriers - block fertilization from occurring by

• impending different spices from attempting to mate 

• preventing the successful completion of mating 

• hindering fertilization if mating is complete  

• Habitat isolation

  • 2 species occupy different habits within the same areas may encounter each other rarely if at 

• Temporal isolation

  • Spices that breed at different times of the day, different season, or different years cannot mix their gametes  

•  behavioral isolation 

  • Courtship rituals and other behaviors unique to species are effective barriers to mating 

• mechanical isolation 

  • Mating is attempted but morphological difference prevent its successful completion 

• gametic isolation

  • sperm of one species may not be able to fertilize eggs of another species    

Post zygotic barriers - prevent hybrid zygotes from developing into viable fertile adults through  

• reduced hybrid viability 

• Genes if different parent species may interact in way that impair the hybrids development or survival in its habitat 

• Reduced hybrid fertility

  • Meiosis may fail to produce normal gametes resulting in sterility if the parent species have chromosomes of different number or structure 

• hybrid breakdown 

  • First generation hybrids are viable and fertile but offspring in the next generation are feeble or sterile 

• mating and fertilization occur and a zygote is formed 

Allopatric vs sympatric speciation 

Allopatric - speciation that begins with geographic isolation. Population live in different areas are in allopatry, they live in a different homeland  

• Dispersal - movement of individuals form one location to another 

• Vicariance - physical splitting of a habitat a physical barrier splits population into subgroups that are physically isolated (river, canyon, ocean, pangea) 

• Geographic isolation, genetic isolation, genetic divergence 

Sympatric - populations that live in the same geographic area, speciation that occurs among populations within the same geographical area 

• External - disruptive selection based on different ecological niches or mate preferences 

• Extrinsic  

• Intrinsic - one type of mutation polyploidy, condition of possessing more than two complete sets of  chromosomes caused by massive error in meiosis or mitosis 

• No geographic isolation, genetic isolation, genetic divergence

• Polyploidy - possessing 2 or more complete sets of chromosomes  

  • Most plant species are the result of polyploid speciation 

  • Plants are much more robust to abnormal chromosome numbers, as long as they can do what they need to survive they will 

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Phylogeny 

Speciation - the splitting of a species into 2 or more independent species 

Tip - taxa are located on the tip because none of the taxa are presumed to be ancestors on others, living in present time 

Branch - a line representing an evolutionary lineage, each position represents an ancestor 

(node) branch point - common ancestor of dierging evolutionary lineages, most common recent ancestor, represents speciation events 

Rooted tree - common ancestor of all taxa on the phylogenetic tree 

Sister taxa - closely related taxa that share a recent common ancestor 

Shared ancestral character- a character that originated in an ancestor of the taxon 

Shared Derived character - an evolutionary novelty unique to a particular clade

Synapomorphis - found in 2 or more taxa present in their most recent common ancestor and missing in more distant ancestor 

Clade (monophyletic groups) - a group that includes the common ancestor and all of the descendents, Clades are nested, like russian nesting doll there are clades within clades 

Paraphyletic group - consists of an ancestral species and some but not all of the descendant, the common ancestor to all members of the group is part of the group  

Polyphyletic group - group includes distantly related species but not their most recent common ancestor  

• Monophyletic group - a group that consists of an ancestor and all of its descendants, representing a complete branch on the tree of life, which is useful for understanding evolutionary relationships.