chapter 3 biology

• CHAPTER 3.0: SELECTION & SPECIATION (1 Hour Lecture) (3 Hour Tutorial)
• Selection & Speciation (An Overview)

  • Selection
  • Speciation
• Types of Selection

  • Natural selection
  • Artificial selection
• Natural selection

  A process by which 1 or more factors acts on various phenotypes within a population, resulting in different ability to survive and reproduce successfully in a specific habitat
• Artificial selection


  A selective breeding of domesticated plants & animals to encourage the occurrence of desirable traits
• Types of natural selection

  • Stabilizing selection
  • Disruptive selection
  • Directional selection
• Stabilizing selection


  Natural selection that favours individuals having intermediate phenotypes by acting against both extreme phenotypes
• Stabilizing selection


  • Human birth weight
  • Egg weight in ducks & chickens
• Disruptive selection


  Natural selection that favours individuals on both extreme phenotypes by acting against intermediate phenotypes
• Disruptive selection


  • Beak sizes of Darwin finches
• Directional selection

  Natural selection that favours individuals on 1 extreme phenotype by acting against individuals on the other extreme
• Directional selection


  • Color of peppered moth
  • Antibiotic resistant bacteria
• Inbreeding


  Selective mating between closely related individuals that have similar genotypes for the selected character
• Inbreeding

  • Self-fertilization
  • Crossing between individuals from the same parents
  • Marriage between relatives
• Outbreeding

  Mating between unrelated individuals or individuals from different populations
• Inbreeding increases homozygous genotypes to maintain the desirable phenotypes
• Inbreeding is usually practised by breeders & farmers to produce good breed of livestock & pets
• Outbreeding introduces new genetic variation into a population
• Inbreeding

  Increases homozygous genotypes to maintain the desirable phenotypes
• Inbreeding

  • Self fertilization
  • Crossing between individuals from the same parents
  • Marriage between relatives (cousin)
• Modern corn that arises from its ancestors, teosinte
• Maize with large & long cobs is self fertilized for many generations
• Inbreeding depression


  Inbred individuals have lower fitness (measured as the average number of surviving offspring)
• Disadvantages of inbreeding

  • Decrease genetic variation
  • Become less fertile (lower reproduction)
  • More susceptible to disease (lifespan decreases / less resistance to diseases)
• Outbreeding

  Selective mating between unrelated or distantly related individual that have different genotypes for the selected character
• Outbreeding

  Increases heterozygous genotypes
• Outbreeding

  Each homozygous individual may carry some dominant allele
• Outbreeding

  Heterozygote individual carry all dominant alleles
• Hybrid vigour

  Hybrid are genetically superior than parents
• Outbreeding increases genetic variation
• Oil palm (Elaeis guineensis) varieties

  • Dura
  • Pisifera
  • Tenera
• Outbreeding in oil palm

  1. Pollen from Pisifera (male parent) is transferred to Dura female flowers

  2. Obtain seeds (Tenera variety)
• Hybrid


  • Parent 1 has larger diameter but shorter cobs
  • Parent 2 has smaller diameter but longer cobs
  • Hybrid has both larger diameter & longer cobs
• Importance of Artificial Selection

  • Produce higher quality of food
  • Produce higher yield of food
  • Animals are bred to do a particular job
• Biological Species Concept

  A population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring (but do not produce viable, fertile offspring with members of other such group)
• Problems of Biological Species Concept

  • Only applies to sexually reproducing organisms
  • Cannot determine the ability of the extinct organisms to interbreed
  • Not possible to determine population that are separated geographically whether they would interbreed in nature
  • Many different species that live together do not interbreed in nature but can interbreed if brought into artificial environment
• Deme

  Small interbreeding populations that organisms belonging to the same species exist as
• Speciation

  Formation of a new species from a single ancestral (previously existing) species by evolution
• Modes of Speciation

  • Sympatric
  • Allopatric
• Sympatric Speciation

  Formation of 2 or more species from a single ancestral species that occupy the same geographic area or geographically overlapping population