-describes the gene pool of a non-evolving population

-states that the frequencies of alleles and genotypes in a gene pool remain constant over generations (said to be in equilibrium)

1. Very large population size
2. No migration
3. no net mutations 
4. random mating
5. no natural selection

1. Natural Selection
2. Genetic Drift 
3. Gene Flow
4. Mutations 

Gene Flow

-a change in an organism's DNA can immediately change a gene pool 

-original source of all genetic variation

-serves as the raw material of natural selection 

Genetic Variation

-variation is necessary for natural selection, helps to ensure the long-term survival of a species

-can be quantitative (varies along a continuum, skin color) or discrete (only set possiblilities, blood type)

*quatitative inheritance is called polygenic inheritance, usually coded for by more than one gene 

1. Gene Diversity- the average percentage of the hertozygous alleles
2. Nucleotide Diversity- percentage of DNA bases that vary between two individuals 

-most species exhibit some kind of geographic variation (differences in gene pools between populations of the same species)

-Cline: gradual change in a trait along a geographic axis 

1. Mutations 
2. Sexual Recombination (crossing over, independent assortment, and random fertilization)

-Diploidy: "two alleles". Recessive traits are often hidden and passed on to the next generation through a heterozygote, advantage is that if the environment changes, the recessive allele may be selected for. 

-Balanced Polymorphism

-the ability of natural selection to maintain diversity within a population

1. Heterozygote Advantage (sickle cell anemea and malaria)

2. Frequency Dedpendent Selection (the survival and reproduction of one phenotype decreases if the phenotype becomes too common)

3. Nuetral Variation (has little or no impact on reproductive success, ie fingerprint diversity.  Not affected by natural selection)

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

-how many offspring you have

-the contribution of a genotype to the next generation compared to the alternative genotypes 

-ex: RR: 80% more offspring than R_

       rr has a relative fitness of .80

       R_ has a relative fitness of .20

-a change in the environment favors individuals at the extremes

-ex: patchy environment, midtone stands out

-a change in the environment shifts away from the extremes 

-ex: birthweight for babies

-direct competition between the individuals of one sex (usually the males) for mates

-males use secondary equipment (antlers) to battle their competition

1. Evolution is limited by historical constraints (we can only evolve so far- we can walk upright but can't birth well)
2. Adaptations are often compromises (limber limbs give us flexibility, but we also get sprained joints)
3. Not all evolution is adaptive (some times populations are wiped out by chance, black plague)
4. Only existing variations can be selected  for (advantageous mutations need to occur)

-The origen of new species

-Two patterns of speciation:

      1. Anagenesis- one species transforms 

          into another

      2. Cladogenesis- one species branches

          off from another (more diversity)  

1. Prezygotic Barriers- prevent fertilization of egg cell (Habitat, Behavorial, Temporal, Mechanical, and Gametic Isolation (sperm either can't survive in or recognize the female reproductive tract))
2. Postzygotic Barriers- complete development of the fertilized egg is prevented (Reduced hybrid viability, reduced hybrid fertility, hybrid breakdown)

-a geologic separation must happen

-more likely to occur if the population is small 

-isolated species becomes different enough to no longer enterbreed with the original population 

-in geographically overlapping regions 

-a new species arises within a parent species

-relatively rare in animals, common in plants (plants can self pollinate is polyploidy occurs, giving the plant two extra sets of chromosomes)