General-Biology 2

• Species


  Classification comprising related organisms that share common characteristics and are capable of interbreeding
• Interbreeding


  The act of mixing different species or varieties of animals or plants to produce hybrids
• Zygote


  Fertilized egg cell resulting from the union of a female gamete (egg, or ovum) with a male gamete (sperm)
• Reproductive Isolation


  Inability to interbreed
• Speciation


  The formation of two species from one original species
• Reproductive Isolating Mechanism


  Mechanisms that prevent interbreeding
• Objective


  Distinguish the various types of reproductive isolating mechanisms that can lead to speciation
• Pre-zygotic Isolation


  Mechanisms that prevent fertilization and zygote formation before fertilization
• Post-zygotic Isolation


  Mechanisms that allow fertilization but result in nonviable or weak hybrids after fertilization
• Geographic or Ecological or Habitat Isolation


  Potential mates occupy different areas or habitats, preventing contact
• Temporal or Seasonal Isolation


  Different groups may not be reproductively mature at the same season, month, or year
• Behavioral Isolation


  Differences in courtship patterns
• Mechanical Isolation


  Morphological differences prevent successful interbreeding
• Gametic Isolation


  Incompatibilities between egg and sperm prevent fertilization
• Hybrid Inviability


  Fertilized egg fails to develop past the early embryonic stages, resulting in inviable hybrids
• Despite their superficially similar appearance, D. melanogaster and D. simulans have incompatible alleles for nuclear pore proteins
• Dysfunction of this vital gene results in inviable hybrids
• Rana draytonii and Rana catesbeiana have been separate for tens of thousands of years
• If zygotes form between Rana draytonii and Rana catesbeiana, they are inviable
• The separation of Rana draytonii and Rana catesbeiana has created a conservation problem in areas where Bullfrogs have been introduced in Red-legged Frog habitat
• Bullfrogs will voraciously eat juvenile frogs
• Hybrids are sterile because gonads develop abnormally or there is abnormal segregation of chromosomes during meiosis
• Hybrid Sterility is an example of post-zygotic isolation
• Example 1 of Hybrid Sterility: Tigers (Panthera tigris) and Lions (Panthera leo) produce sterile hybrid offspring like ligers and tigons
• Non-homologous chromosomes lead to meiotic dysfunction in hybrid sterility
• Example 2 of Hybrid Sterility: Horse (Equus caballus) and Donkey (Equus asinus) produce sterile hybrid offspring like mules and hinnies
• F1 hybrids are normal, vigorous, and viable, but F2 contains many weak or sterile individuals
• Hybrid Breakdown is another post-zygotic isolation mechanism where F1 offspring are fertile but successive generations suffer lower viability or fecundity
• Example of Hybrid Breakdown: Rice cultivars have fertile F1 hybrids but the F2 generation is stunted and sterile
• Speciation is the formation of two species from one original species
• Allopatric Speciation occurs when some members of a population become geographically separated from the others, preventing gene flow
• Examples of geographic barriers in Allopatric Speciation include bodies of water, mountain ranges, and groups of organisms traveling to new locations without the ability to return
• Biologists group the allopatric process into two categories: Dispersal and Vicariance
• Examples of group of organisms traveling to a new location without the ability to return

  • Seeds floating in the ocean to an island
• Allopatric speciation


  Biologists group allopatric process into two categories: Dispersal and Vicariance
• Allopatric speciation


  • Along the west coast of the United States, two separate subspecies of spotted owls exist. The cause of initial separation may have been caused by the glaciers of the ice age dividing an initial population into two
• Northern spotted owl


  Has genetic and phenotypic differences from its close relative, the Mexican spotted owl, which lives in the south
• Adaptive population


  The varied demands of their new lifestyles lead to multiple speciation events originating from a single species
• Sympatric speciation


  Occurs when members of a population that initially occupy the same habitat within the same range diverge into two or more different species
• Sympatric speciation


  One form can begin with a chromosomal error during meiosis or the formation of a hybrid individual with too many chromosomes