Transcript Slide 1
– 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