15.2 Species and Speciation Overview
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Transcript of 15.2 Species and Speciation Overview
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15.2 Species and Speciation OverviewI. Evolution
I. Results of evolutionI. New species (speciation)
II. Causes of evolutionI. Barriers between same species (gene pools)
I. Geographical isolation -> leads to allopatric speciationII. Temporal isolation -> leads to sympatric speciationIII. Behavioral isolation -> leads to sympatric speciationIV. Hybridization -> leads to sympatric speciation
III. Types of EvolutionI. Adaptive radiationII. Convergent evolutionIII. Divergent evolution
IV. Pace of EvolutionI. GradualismII. Punctuated equilibrium
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• Gene pool – all of the genetic information present in the reproducing members of a population at a given time– A large gene pool exists in a population which
shows high variation– A small gene pool exists in a population which
shows little variation (ex: inbreeding)
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• Allele frequency – measure of the proportion of a specific variation (allele) of a gene in a population; this can be stated as a proportion or a percent– Remember, Hardy-Weinberg discussed this in
terms of p and q where: p = frequency of the dominant allele q = frequency of the recessive allele and together p + q = 1
– If there are no changes in allele frequency over time, then no evolution
– If there is big change in allele frequency over time, evolution has occurred
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Review of what can change allele frequencies (and therefore the gene pool) within a
population:1. Mutations2. Immigration and emigration3. Nonrandom mating (ex: inbreeding/selective
breeding)4. Some alleles are more advantageous than
other alleles5. The population is small and therefore the
allele frequencies are easier to manipulate
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• Species – the basic unit for classifying an organism
• A species is made up of organisms which:– Have the ability to interbreed and produce fertile
offspring– Share the same ecological niche– Have the same karyotypes– Have a common phylogeny (share common
ancestor(s))– Share a unique collection of structural and
functional characteristics
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Barriers between Gene Pools
Barriers may exist where populations of members of the same species can be stopped from reproducing together; such barriers can be geographical, temporal, behavioral, or related to infertility caused by hybridization
This slide is an overview of what is to come, no need to write it down!
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Allopatric Speciation• When a new species forms from an existing species
due to a geographic barrier
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1. Geographical Isolation
• Occurs when physical barriers such as land or water formations prevent mating– Ex: tree snails in Hawaii, 1
population lives on trees on one side of a volcano, the other population lives on trees on the other side of the volcano
Type of Allopatric Speciation!
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Sympatric Speciation• When a new species is formed
from an existing species while living in the same geographic area– This is much rarer than allopatric
speciation
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1. Temporal Isolation• Occurs when two populations
mate or flower at different times of the year– Ex: the female parts of one
flower’s population reach maturity before the pollen of another flower’s population gets released
– Ex: one population of mammals is still hibernating while another population is ready to mate
Type of Sympatric Speciation
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2. Behavioral Isolation• Occurs when one population’s lifestyle and habits
are not compatible with those of another population– Ex: many birds rely on courtship displays to attract
mates; if one population has a version of the courtship display which is significantly different from another population, they may not consider each other to be seductive enough to mate with
Type of Sympatric Speciation
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3. Hybrids• Hybrids are typically infertile and
therefore cannot pass on their karyotype– This goes for plants and animals– female horse + male donkey = mule– male horse + female donkey = hinny– female tiger + male lion = liger– male tiger + female lion = tigon
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How polyploidy leads to speciation:• Speciation is when a population
evolves significantly enough so that the production of offspring with the original population becomes impossible
• Haploid – sex cells are monoploidy (n)
• Diploid – somatic cells are diploidy (2n)
• Polyploidy = more than 2 sets of chromosomes; 3n, 4n, 5n, ect.
•Ploidy changes among angiosperms are common including banana tree, tobacco plant, apple trees
•Also seen in animal kingdom with salamanders, frogs, and leeches
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• Studies have shown after polyploidy formation rapid changes in gene structure and expression can occur; if one population evolves enough to have significant change, then a new species can be formed
• NOTE: two similarly polyploidy organisms can interbreed ex: 8n sugar cane with another 8n sugar cane