BIOL 226 Lecture Notes - Lecture 3: Speciation, Gene Flow, Sexual Selection
3 May 2018
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Biol226-Ch24
The Origin of Species
Speciation:
Process by which one species splits into two or more species.
Yield in new species
Micro evolution:
Changes over time in allele frequency in a population
Macro evolution:
Broad pattern of evolution above the species level
Biological species concept:
Individuals that share a gene pool
What holds the gene pool of a species together, causing its members to resemble each other more than
they resemble other species?
Gene flow: exchanging alleles between populations,
the absence of gene flow plays a key role in the formation of new species, as well as in keeping them
apart once their potential to interbreed has been reduced
Reproduction isolation:
the existence of biological factors (barriers) that impede members of two species from interbreeding
and producing viable, fertile offspring.
Prezygotic barriers:
block fertilization
If a sperm cell from one species overcomes prezygotic barriers and fertilizes an ovum from
another specie
ii) Habitat: Two species that occupy different habitats within the same area may encounter each
other rarely, if at all, even though they are not isolated by obvious physical barriers, such as
mountain ranges.
iii) Temporal: Species that breed during different times of the day, different seasons, or different
years can- not mix their gametes.
iv) Behavioral Isolation: Courtship rituals that attract mates and other behaviors unique to a species
are effective reproductive barriers, even between closely related species.
v) Mechanical Isolation: Mating is attempted, but morphological differences prevent its successful
completion.
vi) Gametic Isolation: Sperm of one species may not be able to fertilize the eggs of another species.
Postzygotic barriers:
may contribute to reproductive isolation after the hybrid zygote is formed
ii) Reduced Hybrid Viability: The genes of different parent species may interact in ways that impair
the hybrid’s development or survival in its environment.
iii) Reduced Hybrid Fertility: Even if hybrids are vigorous, they may be sterile. If the chromosomes of
the two-parent species differ in number or structure, meiosis in the hybrids may fail to produce
normal gametes.
iv) Hybrid Breakdown: Some first-generation hybrids are viable and fertile, but when they mate with
one another or with either parent species, off- spring of the next generation are feeble or sterile.
Document Summary
Process by which one species splits into two or more species. Changes over time in allele frequency in a population. Broad pattern of evolution above the species level. The absence of gene flow plays a key role in the formation of new species, as well as in keeping them apart once their potential to interbreed has been reduced. The existence of biological factors (barriers) that impede members of two species from interbreeding and producing viable, fertile offspring. Characterizes a species by body shape and other structural features and suggest that each species is morphologically distinct. No need of absence of gene flow. Sum of how members of the species interact with the nonliving and living parts of their environment: allotropic, sympatric. Defines a species as the smallest group of individuals that share a common ancestor, forming one branch on the tree of life. Gene flow is interrupted when a population is divided into geographically isolated subpopulations.
