Species Genetically Distinct Populations

Natural Selection Driving force for change Competition for resource(s) – Winner survives or thrives more “Best Fit” => Dominant Reproducer – Spectrum of traits exist. – Trait(s) capitalizes on procurement of resource(s) Time tells. – Most successful feeder = best mate = most genes

Gene Pool Sum of all individual genes in a population – Variations of genes = alleles Allele frequency = # of a certain allele/ total # of alleles – Out of 10 possible alleles, 4 are A. 4/10 = 0.4 or 40% – Chance of 2 alleles combining = (freq A)(freq A) = 0.16 Different combinations => different phenotypes – Phenotype = physical manifestation of trait Phenotype frequency= # certain phenotype/# people – Catastrophe leads to limited survivors Chance determines who gets hit

Hardy-Weinberg Genetic Equilibrium Ideal, hypothetical, non-evolving population Assumptions – No net mutations occur (alleles stay constant) – No one leaves or enters (population is constant) – Population is large (ideally, infinitely so) – Individuals mate randomly – Selection does not occur

Mutation Occur spontaneously, constantly, normally Accelerated with mutagens – Radiation and certain chemicals Natural selection acts on phenotypes, not alleles individually Recessive alleles “hidden” in heterozygotes Beneficial mutations vital to evolution

Gene Flow Immigration (moving into population) Emigration (moving out of population) When organisms move, their genes move too Typically occurs when younger males move out, individuals migrate, natural disasters hit Plants routinely disperse their seeds/ spores

Genetic Drift When allele frequencies change due to random events More noticeable in small populations Essential for survival of species/ population Diversity of alleles in gene pool gives greater nuances of traits Natural selection works on variants – The more traits, the better the species survival

Nonrandom mating Sexual Selection – Female typically chooses male Geographical Isolation – Original population divided Reproductive Isolation – Barriers to successful breeding in same area – Prezygotic isolation (premating) – Postzygotic isolation (postmating)

Species Concepts A population that can successfully interbreed but not with other groups (Biological) Organisms that have same internal & external appearances (Morphological) Modern definition includes parts of both – A single kind of organism – Morphologically similar – Interbreed to produce fully fertile offspring

Speciation Allopatric speciation (“different homelands”) – Geographical isolation = no gene flow – More likely in smaller populations Smaller gene pool is more affected by genetic drift & natural selection Sympatric speciation (“same homeland”) – Use of different niches  adaptive advantage – Specialization  reproductive isolation

Rates of Speciation Gradualism – Regular, gradual rate – Selective pressures are fairly constant Punctuated Equilibrium – Occurs in “bursts” – Rapid, sudden changes due to catastrophe – Some species exist for long time, but other new forms appeared in only a thousand years or less