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– species - naturally occurring group of organisms that can
successfully interbreed and produce fertile offspring; usually
unable to breed with organisms outside that group
– subspecies and strains - differ from other members of the
species in genetic composition and in the phenotypic
expression of that composition
Example: Canada geese mate for life and return to the same
place to breed every year; this behavior has produced
several subspecies that rarely interbreed
– this may seem unimportant, but it’s been found that if one
subspecies is lost other members of the species poorly fill
the geographic range
Example: Audubon bighorn sheep – this subspecies went
extinct in early 1900’s, and efforts to re-introduce other
bighorn sheep subspecies has not been very successful
– aquaculture (culture and husbandry of aquatic organisms)
and game ranching/farming (husbandry of native or exotic
animals, usually large ungulates, for meat or sport) has
artificially increased number of strains
Isolating Mechanisms - keeps organisms from interbreeding
and keeps gene pools segregated
– allopatric - populations of closely related species that have
non-overlapping geographic ranges; genes will not mix b/c
of geographic separation; they may eventually become a
new species; could be separated by geologic (mountain
building, flood event) or climatic (glaciers, rise in sea levels)
event
– sympatric – speciation while ranges overlap; isolating
mechanisms keep them from interbreeding
Allopatric
Speciation
Sympatric
Speciation
— possible differences for reproductive isolation:
- behavioral (mating rituals)
- physiological (different breeding season)
- anatomical (mating apparatuses are different)
— natural developmental abortion or hybrid sterility will
keep offspring from further success
– if allopatric species are brought back together and they
successfully interbreed with viable offspring then the 2 are
not separate species
Natural Selection
– organisms of different genotypes in a population contribute
differently to the gene pool; those most successful in an
environment will survive better and produce more offspring
with their traits
– adaptation - the change in structure, physiology, behavior,
or mode of life that that allows a species to adjust to its
environment; changes occur because of differential survival
of offspring
– alleles are not lost when they are no longer advantageous,
just greatly reduced, so the gene that contains the allele
remains heterozygous in the population and may benefit later
Example: pepper moth of England; dark or light colored
Individuals dominate the population depending on pollution
level
– changes may happen too rapidly for a species to adapt and
they are lost; dinosaurs
– convergent evolution - species with different origins develop
similar traits to occupy similar niches; flightless birds,
marsupial analogues to mammals
Artificial Selection - humans choose parents based on
phenotypic traits; we breed animals for desired traits
– offspring may lack fitness because they are adapted to an
artificial habitat; farmed turkeys would never make it in a
natural environment, most are white and too fat
Inbreeding - mating between closely related species; usually
happens in small populations (endangered species)
– inbreeding depression - a reduction in fitness due to
increased homozygosity; bad alleles accumulate;
hemophilia in British Royal family
– founder effect - a few individuals establish a new population
and inbreeding occurs; population only has genes of
founding parents; occurs in island populations or exotics
– outbreeding - mating between individuals that are very
distantly related; may not be a good idea because some
adaptations to local environments can be lost
– must keep heterozygosity in populations and this must be
closely monitored in small populations
Hybrids - offspring from mating of parents that are genetically
unlike (2 different species); a mule is a hybrid of a male
donkey and a female horse
– could get a more heterozygous, fit individual as a result
(hybrid vigor) but in most cases this is not a desirable thing
Other Genotypic Change Processes
– mutation - DNA may change chemically through copy
errors, radiation (UV, X-ray), or chemical reactions
– chromosome aberrations - deletion, duplication, inversion,
or translocation
– genetic drift - random changes in allele frequencies due to
breeding success; biggest contributor to evolution
– genetic engineering - involves gene transfer of desired
DNA to organisms; triploid animals often cannot reproduce
and grow fast (fisheries mostly) since no energy is put into
reproduction