L3: Evolution BIOLOGY

• What is Evolution?

  Change in the heritable characteristics of biological populations over successive generations.

  How?

  Mechanisms of evolution act on this variation, resulting in certain characteristics becoming more common or rare within a population.

  Result.

  Given rise to BIODIVERSITY at every level of biological organization
• Artificial Selection means

  Humans Identify the desirable traits in plants and animals. Steps taken to enhance and perpetuate those traits in future generations. It is done via SELECTIVE BREEDING, CROSS BREEDING and INBREEDING (to preserve the desired trait.
• Natural selection, or "SURVIVAL OF THE FITTEST," is the more prolific reproduction of individuals with FAVORABLE TRAITS THAT SURVIVE ENVIRONMENTAL CHANGE because of those traits. This leads to evolutionary change.
• DIVERGENT EVOLUTION

  is a type of evolution in which new species evolve from a shared ancestral species. At some point in history a geographical barrier has divided the population into two or more populations and has also interfered the interbreeding between the populations.
• CONVERGENT EVOLUTION

  is the result of similar selection pressures in the environment selecting for similar features or adaptations. These adaptations have not been inherited from a common ancestor. Similar traits evolve independently in species that do not share a common ancestry.
• COEVOLUTION

  refers to the evolution of one organism in response to another organism.
• Gene Flow means two or more species of different population interbreeds when one migrates to the other.
• Genetic Drift: Bottleneck Event

  Genetic drift is the change of allele frequencies as a result of chance process. In a Bottleneck Event, a disaster happens and part of the population dies but other survive out of good chance resulting in genetic drift.
• Bottleneck Event: Several times, green beetles were killed when someone stepped on them. The next generation would have a few more brown beetles than the previous generation - but just by chance or luck.
• Mutations it generates the genetic variation on which the evolutionary process depends
• Genetic Drift: Founder Effect

  A magnification of genetic drift in a small population that migrates away from a large parent population carrying with it an unrepresentative set of alleles. The occurrence of the recessive trait will become more frequent if these small portion of the original population expresses the recessive trait. As a result, the once recessive trait turns to be dominant trait within their group.
• Evolutionary Modification Reproductive Isolation Mechanism

  • Reproductive isolation mechanisms are collection of evolutionary mechanisms, behaviors, and physiological processes that prevent members of different species from producing offspring or ensure that any offspring are sterile. These barriers maintain the integrity of a species by reducing gene flow between related species.
• Pre-zygotic isolation mechanisms prevent fertilization and zygote formation
• GEOGRAPHIC OR HABITAT ISOLATION potential mates occupy different areas or habitats thus, they never come in contact.
• TEMPORAL OR SEASONAL ISOLATION different groups may not be reproductively mature at the same season.
• BEHAVIORAL ISOLATION patterns of courtship are different despite of being close species
• MECHANICAL ISOLATION differences in reproductive organs prevent successful interbreeding;
• GAMETIC ISOLATION incompatibilities between egg and sperm prevent fertilization.
• Evolutionary Modification Reproductive Isolation Mechanism

  • Prevents Fertilization
  • Prevents Mating
• Post-zygotic isolation mechanisms allow fertilization but nonviable or weak or sterile hybrids are formed.
• HYBRID INVIABILITY

  fertilized egg fails to develop maturity or dies after embryonic stage(s) of development
• HYBRID STERILITY

  hybrids are sterile because gonads develop abnormally, (no healthy sex cells produced)
• HYBRID BREAKDOWN

  F1 hybrids are normal, vigorous and viable, but F2 are weak or sterile individuals
• SPECIATION

  An evolutionary process by which populations evolve to become distinct species
• ALLOPATRIC SPECIATION OR GEOGRAPHIC SPECIATION

  (allo-other, patric - place; 'other place') - occurs when some members of a population become geographically separated from the other members thereby preventing gene flow.

  Examples of geographic barriers are bodies of water and mountain ranges
• PERIPATRIC SPECIATION

  (peri-around, patric - place; 'around place') - a new species is formed from an isolated peripheral population. Occurs when the size of the isolated subpopulation is small.
• PARAPATRIC SPECIATION

  (para-beside, patric place; 'beside each other') - occurs wher the groups that evolved to be separate species are geographic neighbors. Gene flow occurs but with great distances is reduced.
• SYMPATRIC SPECIATION

  (sym-same, patric - place; 'same place') - occurs when members of a population that initially occupy the same habitat within the same range diverge into two or more different species. It involves abrupt genetic changes that quickly lead to the reproductive isolation of a group of individuals.