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Class notes introductory biology (BIOL1010) Lesson 11
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The Origin of SpeciesBiological Species Concept: A group of populations whose, members have the
potential to interbreed in nature and produce viable offspring but are not viable with
other species
Prezygotic reproduction: Blocks fertilization from occuring (pg.524)
● Habitat Isolation
● Temporal Isolation
● Behavioural Isolation
Mating attempted
● Mechanical Isolation
● Gametic Isolation
Postzygotic reproduction: If fertilized, barriers occur to stop hybrids survival
● Reduced Hybrid Viability
● Reduced Hybrid Fertility
● Hybrid Breakdown
Limitations
● Biological species concept does not apply to organisms reproducing asexually
How species are kept separate
● After fertilization postzygotic barriers occur
● Absence of gene flow keep species separate
● Natural selection
Morphological species concept: Characterizes a species by body shape and
structural features
Ecological species concept: Ecological niche, sum of how members of the species
interact with the nonliving and living.
Phylogenetic species concept: smallest group of individuals that share a common
ancestor. Compares characteristics like morphology, molecular sequences with those of
other organisms.
(pg.530)
, Allopatric speciation: Gene flow interrupted when population is divided into
geographically isolated subpopulations. Alters allele frequencies.
Sympatric speciation: live in the same geographical location. Occurs with reduced
gene flow by polyploidy, habitat differentiation and sexual selection.
Autopolyoid speciation: Individuals that have more than two chromosome sets
derived from a single species. Occurs when two different species interbreed and create
a hybrid.
Allopolyploid speciation: Fertile polyploid, fertile when mating with another but cannot
interbreed with parent species.
Hybrid zones: Region where members of different species meet and mate
● Reinforcements
○ Hybrids less fit than members of their parent species
○ Natural selection strengthens prezygotic barriers
○ Stronger in sympatric than allopatric populations
● Fusion
○ Barriers to reproduction are not strong
○ Gene flow causes species to become increasingly alike
○ Causes hybridizing species to fuse into one species
● Stability
○ Hybrid zones are stable
○ Hybrids are more fit than either parent species
Genetic changes and speciation
● Caused by mutations, causing different proteins to be produced.
● Specialization can happen
Fossil Record
● Sedimentary rock layers call strata
● Biased to species the existed for a long time
● Dated by radiometric dating
○ Measures the decay of radioactive isotopes
○ Expressed by half-life, the time required for 50% of the parent isotope to
decay
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