74 terms

Evolution Exam 2

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Phylogeography
the study of the historical processes leading to the distribution of closely related individuals
Biodiversity
biological diversity
The variation in form and function of living organisms
Can be applied to present or past levels of biodiversity
Is frequently applied as a measure of the health of biological communities
Species richness
a count of species that occurred during a particular time or in a particular place
Groups of plants and animals with high origination rates (speciation), also have high extinction rates -> they have a greater species turnover
Possible reasons for this:
Degree of ecological specialization
Species capable of specialization are more likely to speciate, but are also more likely to be vulnerable to environmental changes


Population dynamics
Species with small or fluctuating population sizes are more likely to go extinct

Geographic range
Species with smaller ranges face a greater threat of extinction
Species with broad ranges tend to have higher dispersal capabilities and wider ecological tolerance
Competitive displacement
competition among two groups causing extinction
As numbers of one group increases, the less competitive group decreases
Incumbent replacement
extinction allowing a species to move into an available niche
One group preventing another group from diversifying
Gene
a region of DNA which is transcribed to mRNA
Control region
untranslated regions where enhancers and repressors bind to regulate translation
Exons
the translated regions of the gene
Introns
sections of the gene that are transcribed but are not translated
Alternative splicing
when exons are removed from the final mRNA that will be translated
codons
3 nucleotide sections (codons) which specify which amino acid should be attached to the polypeptide chain
Synonymous mutation
those that do not change an amino acid
Nonsynonymous mutation
those that do change an amino acid
Gene families
groups of genes that are similar in sequence and function
Human hemoglobin has two subfamilies found on two different chromosome
Mutation
the process of alteration of a sequence of DNA
Wild type
the normal/common form of a gene in a population
Point mutation
change in a single base pair
transition: substitution of a purine to purine, or pyrimidine to pyrimidine
transversion: change from a purine to pyrimidine or vice versa
Frameshift mutations
a mutation that adds or deletes one or more nucleotides to a sequence, changing the downstream codons
Indel
abbreviation for "insertion/deletion", frequently it is unclear if nucleotides have been added or removed
Independent assortment
when nonhomologous chromosome pairs align and separate randomly
Crossing over
when non-sister chromatids of homologous chromosomes exchange pieces
Intragenic recombination
when recombination occurs within gene
Unequal crossing over
when two homologous sequences or chromosomes are not perfectly aligned
Transposable elements
segments of DNA sequence which can self replicate and become inserted into other regions of the genome
pleiotropic
impacting many characters
Karyotype
the description of an organisms complement of chromosomes; number, size, shape, internal arrangement
Polyploidy
when a organism has multiple sets of homologous chromosomes
phenotypic plasticity
one genotype to produce more than one phenotype when exposed to different environments. Phenotypic plasticity is the ability of an organism to change its phenotype in response to changes in the environment.
Norm of reaction
the variety of different phenotypes that can be produced by a single genotype under different environmental conditions
Cultural Inheritance
behavioral traits that are learned from adult individuals
e.g. language
Can lead to divergence among populations/species
Maternal effect
variation that is not genetic, but due to factors such as maternal care or yolk composition
Epigenetic inheritance
phenotypic differences that are transmitted among generations of cells but are not based on DNA sequence differences
i.e. DNA methylation eliminating a DNA transcript
Allele frequency
proportion of a population carrying a specific allele
Genotype frequency
the proportion of a population with a specific genotype
Hardy-Weinberg equilibrium
states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences
Causes of Non-HWE
Population is not mating at random
The population is finite -> genetic drift is occurring (random loss of variation)
Gene flow -> alleles are coming in from another population
Mutation -> changing allele frequencies
Different genotypes have higher or lower fitness/survival -> natural selection
All indicate evolutionary change
Inbreeding
when individuals are more likely to mate with relatives than non-relatives
inbreeding coefficient (F)
is the probability that an allele is identical by descent
lethal alleles
that when homozygous lead to death in offspring
Inbreeding depression
when mating among related individuals causes a decline in fitness and survival
Linkage disequilibrium
occurs when loci are commonly associated due to physical linkage or other mechanisms
Quantitative traits
traits that exhibit continuous variation rather than discrete character states - continuous variation
variance
the spread of values around a mean
the sum of the genetic variance and the environmental variance
Heritability
is the amount of genetic variance divided by the total variance (both genetic and environmental)
Artificial selection
when a particular trait is manually selected for
Cline
a gradual change in a character or allele frequency over a geographic distance

i.e. body size increases in white-tailed deer with increasing latitude
Ecotype
a habitat-associated phenotype
-can have both environmental and genetic components
Gene flow
is the exchange of genetic material among populations through mating
Genetic drift
The random fluctuation of allele frequencies due to the chance drawing of gametes that will be transferred to the next generation
Coalescence
the point where all gene copies for a particular locus can be traced to a single ancestor
Effective population size
the number of individuals that equally contribute to the next generation -> number at which the rate of drift would be the same as the actual population size
Bottleneck
when a population goes through a period of very small population size

-Genetic drift will become more significant and large amounts of variation will be lost
-Length of the bottleneck will determine how much variation is lost
Founder effect/event
when a population is established by very few individuals
Neutral Theory
the hypothesis that many genetic polymorphisms are selectively neutral and are maintained by a balance between drift and mutation
Adaptation
a characteristic that enhances survival or reproduction in individuals that carry it
Natural selection
differential survival of individuals that differ in one or more characteristic
Fitness
average per capita rate of increase in numbers

Probability of survival to reproductive age
Average number of gametes produced
Union of gametes to produce viable zygotes
Preadaptation
an existing feature that can serve a new function
Exaptations
preadaptations that serve an entirely new function
Comparative method
comparing sets of species to pose or test hypotheses of adaption and evolution
Directional selection
selection where an extreme phenotype is fittest
Stabilizing selection/Balancing selection
selection where an intermediate phenotype is fittest
Diversifying selection
selection that favors multiple phenotypes
Absolute Fitness
average per capita rate of increase in numbers of a genotype
Relative fitness (w)
the fitness of a genotype relative to other genotypes
Adaptive landscape
a graph of mean population fitness by allele frequencies
Adaptive peaks
A point within the adaptive landscape where there is high fitness
Adaptive valleys
allele frequencies that lead to low population fitness
Purifying selection
directional selection which reduces the frequency of a deleterious mutation
Inverse frequency dependent selection
the rare a genotype the higher its fitness
Positive frequency dependent selection
the fitness of genotype is greater as its frequency increases
Heterozygote disadvantage
when the heterozygote has a lower fitness than either homozygote
Selective sweep
when all individuals carry the same gene copy, and show a more recent common ancestry than neutrally evolving regions
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