Bio 2970 Exam 3

Mayr-A reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature

temporal, ecological, behavioral, mechanical, gametic

hybrid invariability, hybrid sterility, hybrid breakdown

controversial selection on hybrids with postzygotic barriers leads to prezygotic barriers

• 1. sexual forms only
• 2. no temporal dimension-BSC is for a slice of time and does not show lineage through time
• 3. not a single unit of evolution-divergence of character does not equal different species
• 4. not practically testable-sexual behavior in lab doesn't always reflect behavior in habitat

Carcraft-A lineage of ancestor-descendant populations diagnosably distinct by divergence of character

vicariance and founder event

subdivide formerly continuous habitat

rare dispersal across pre existing barrier eg Galapagos

Larson disagrees geographic isolation does not precede evolution of species

multiple species lineages generated from an ancestor in an undivided geographic area

less empirical support accumulation of small, quantitative changes leads to qualitative change

large phenotypic change in a single generation eg Ancon sheep

• a population based mechanism of evolutionary change invoked to explain adaptation
• Not a random process
• Random component-variation is produced at random with respect to organism's needs
• Non-random component-organisms with favorable traits have higher rates of survival and reproduction, causing populations to accumulate the most favorable variants and discard less favorable ones

• Obv1. Organisms have great potential fertility, permiting exponential growth of populations
• Obv2. Natural populations remain fairly constant in size, not increasing exponentially
• Obv3. Natural resources are limited
• Inf1. A struggle for existence occurs in a population
• Obv4. Variation occurs among organisms within a population
• Obv5. Variation is heritable
• Inf2. Varying organisms show differential survival and reproduction, favoring advantageous traits-natural selection
• Inf3. Natural selection over many generations gradually produces new adaptations and species

later forms are superior to early ones in a general sense

• 1. Substrate nutrality-reproducting population with heredity and variation
• 2. Underlying mindlessness
• 3. Guranteed results

a trait that evolved by natural selection for a particular biological role

a trait coopted by natural selection for a role incidental to the trait's origin

• 1. Abstraction and Simplification
• 2. Sufficient Paramaters
• 3. Assumptions

identify essential aspects of reality and remove distracting elements

minimum mumber of summary variables, combining relevent information of many parameters at lower levels eg "fitness"

unreal conditions used to facilitate study eg non-overlap generations, infinite population

DNA can replicate, can mutate and recombine, encodes RNA/proteins that interact with environmental conditions to influence a phenotype

replication without mutation, refering to alleles and associated phenotypes eg mitochondrial DNA

all copies of homologous DNA trace back to a common ancestral molecule

mutations can be good or bad

Set of identical haploid genomes for a specified unit of measurement (same as allele for measurements taken at DNA/chromosomal level)

bases present at polymorphic sites genotypically linked on a DNA molecule eg SNPs RFLPs

branches show lineal descent of copies of homologous DNA

branches denote mutational events in the evolutionary histroy of homologous DNA

a local population of reproducing individuals that has physical continuity over time and space, lowest biological level that can evolve

the population of gene copies and potential gametes collectively shared by individuals of a deme

mutation produced lethal alleles and selection removes them

• µ unitless
• # newly mutated copies
• total # copies of homologous DNA

any measurable trait, either discrete or continuous

• 1. Complexity of the genotype-phenotype relationship-no single factor is both necessary and sufficient to cause a phenotype, causes of variation of a phenotype does not equal cause of a phenotype
• 2. Confoundment of frequency and apparent causation in complex systems-requires population studies

phenotype only observed when homozygous eg sickle cell severe anemia

both phenotypes observed when heterozygous eg sickle cell electrophoretic mobility

presence of one allele masks the phenotype of the other eg sickle cell malarial resistance

heterozygote phenotype is more fit than phenotype of either homozygote eg sickle cell heterozygote viability in malarial environment

genetics is the rarer factor of the disease and the diet is common

diet is the rarer factor of the disease and the genetics is common

Phenotype is the result of only one locus

Ronald Fisher-multiple loci contribute to the phenotype

set of phenotypes associated witha particular genotype in interacton with a variety of environmental conditions and genetic backgrounds

• µ (or ^-x^- for a sample population)
• (x₁+x₂+...+x_n)/n

• σ² (or s² for a sample population)
• σ²=[(x₁-µ)²+(x₂-µ)²+...+(x_n-µ)²]/n
• s²=[(x₁-^-x^-)²+(x₂-^-x^-)²+...+(x_n-^-x^-)²]/(n-1)

σ_p²=σ_g²+σ_e²

analysis of genetic variance for continuously varying phenotypes within a population

how much phenotypic variance is associated with genotypic variation in a population in a given generation

how much of the genetic variance can be transmitted to influence the phenotypic variation in the next generation

g_i= ^-x^-_pog-^-x^-_pop

σ_g²=Σ(freq_geno)(g_i)²

h_B²=σ_g²/σ_p²

g_ai=sum of avg. excess of all phenotypes involved

avg. excess=Σ(freq_allele)(g_i)

σ_a²=Σ(freq_geno)(g_ai)²

h²=σ_a²/σ_p²

• same as non-additive genetic variance in a single locus model
• σ_d²=σ_g²-σ_a² (single locus model)

• 1. Single locus model=σ_d²
• 2. Multilocus model=σ_d²+σ_epistatic²

measures heritability without measuring genotype

• between X and Y
• Avg(X-µ_x)(Y-µ_y)

=(h²/2)+[(σ_d²)/(4σ_p²)

• Between X and Y
• =[Cov(X,Y)]/[sqrt(σ_x²σ_y²)]

=(σ_a²)/2

Hate group that wants to prove that black people are genetically inferior

• locus whose variation contributes to population variation of a continuously varying phenotype
• found using genome scan followed by tree scan

SNP markers every 10 cM in genome of population, which must have high frequency of phenotype and high linkage disequilibrium

• haplotype tree used to test SNP sites for influence on the phenotype
• group all haplotypes on either side of a particular branch, call them A₁ and A₂, measure norms of reaction for the resulting genotypes A₁A₁, A₁A₂, A₂A₂, repeat for all branches in tree

• part of non-additive variance in population level arising from inheritance among genotypes at different loci
• when comparing two populations, the rarer genotype shows more additive variance when epistatically correlated

not sufficient for epistatic variance at population level

Phenotype affected by non-genetic forces, which may include other phenotypes within the body eg LDL cholesterol level

change in allele/gamete frequency in gene pool, fates of alternate forms of genes over space and time ina population

Mutation and Genetic Drift

causes many small changes

random changes in allele frequency due to finite number of population size (sampling error), directionless, cumulative, strength is inversely proportional to 1/(2N), rate of losing allele =1/(2N), avgerage time for two genes to coalesce=2N, avgerage time for all genes to coalesce=4N