Transcript Species - Boyd County Schools

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
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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