Origin of species

• Species is a group of organisms that can interbreed to produce fertile offspring
• Population is a group of individuals of the same species living in the same geographical area
• Cline is the gradual change in a trait/ Allele frequencies across a geographical area
• Deme is a subset of a population that has limited gene flow with member if a larger population
• Flow of reproductive Isolation

  1. Variation- Different trait is selected as beneficial in different area
  2. Geographical Isolation - Division of two subsets (deme) No gene flow
  3. Natural selection - Experiences different selection pressures
  4. Mutation - Accumulation of beneficial mutations(or harmful)
  5. Reproductive Isolation - Unable to interbreed, Changes in behaviour and physiology
• What at the two main isolating mechanisms?Prezygotic and Postzygotic
• Prezygotic are the processes that occur before fertilization

  It is also a barrier that prevents fertilization from happening
• In Pre-zygotic, what are the different types of RIM's? Hint: GEBTMG

  • Geographical
  • Ecological
  • Behavioural
  • Temporal
  • Mechanical
  • Gametic
• Geographical isolation is a Physical separation of populations.
• What is ecological Isolation?

  Reproductive barrier.- occupation/Exploit of different habitats within an area
• Behavioural Isolation:

  Differ in Courtship rituals, sounds and colouration
• Temporal Isolation

  Differ in mating season/ Flowering season
• Mechanical Isolation

  Incompatible Reproductive structures

  Prevents acceptance of gamete
• Mechanical isolation prevents

  Acceptance of gamete
• Gametic Isolation

  Incompatible Gametes, Unable to fuse

  Unable to produce viable offspring
• Post-Zygotic occur After formation of gametes
• In post-zygotic, what are the three possible things that can occur to the Hybrid offspring?

  • Hybrid Inviability-
  • Hybrid Sterility
  • Hybrid break down
• Hybrid Inviability

  Incompatible genes- Dies before birth

  If survived- may dies before its reproductive age
• Hybrid sterility

  Survived Hybrid offspring and sexual maturity

  Sterile- cannot produce viable offspring
• Sterile Hybrid

  Infertile offspring resulting from the crossbreeding of two different species or varieties.
• Hybrid Breakdown

  Hybrid may be viable and capable of producing an offspring

  But the offspring may have reduced fertility and Fitness
• Allopatric speciation occur when two populations are geographically isolated from each other.

  If continued- may lead to reproductive Isolation

  Which overall lead to Speciation
• Speciation: The process by which new species arise
• What are the main pattern of Allopatric Isolation?

  • Geographical Event
  • Separation of niches to reduce competition
  • RIM
  • Geographical Event
  • Speciation
• Sympatric Speciation occurs in same geographical area (Absence of Barriers) - Lead to disruptive Isolation

  Due to Niche Specialisation - Reduce interspecific Competition
• Sympatric Population most commonly occur in

  Plants - Instant speciation during polyploidy
• What the poly mean?

  many
• Three main things that cause polyploidy

  • Caused by errors during cell division
  • Results in cells with more than two copies of chromosomes(>2n)
• Why polyploidy is not a problem in plants?

  
  

  They can self fertilise as the both have male and female sex organs
• What does Auto mean?

  Same
• What does Allo mean?

  Other
• Auto-Polyploidy:

  Multiplication of genome (single species) - Chromosome doubling
• How does Autopolyploidy occur?

  Occurs when Homologous chromosomes don't separate during meiosis(non-disjunction)
• Effect of Non-DisjunctionResults in non reduced diploid gametes (2n) two sets of chromosomes - NOT HAPLOID
• Possible event that can occur in diploid gametes

  If fused in normal gamete haploid (n) - it will become triploid (3n) - Sterile

  If fused with another diploid (2n) through self fertilisation - tetraploid (4n) - Viable
• How does Allopolyploidy occur?

  Two different species produce infertile Hybrid, where chromosomes from both parents are not identical
• What will happen if both parents chromosome are not identical?Cannot pair during meiosis
• What are two possible things that can occur in an sterile Hybrid?Uneven Chromosome number- Meiosis is not possible

  If germinal cells undergo chromosome doubling (allo) meiosis can occur normally= Hybrid species will then be able to produce fertile offspring (gametes)