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CHAPTER 3 : VARIATION - Coggle Diagram

- - - - Chromosome Mutation- Any type of change in chromosome structure or number
      - Gene Mutation- Change in the structure of DNA at a single locus
        
        Insertion
        
        Deletion
        
        Substitution
        
        Inversion
    - - Independant assortment (Metaphase I)
      - Crossing over (Prophase I)
      - Random fertilisation
- - - - Inbreeding
        
        Mating between slosely related individuals where the gametes of the close relatives get fused
        
        Aim : Make sure that desirable characters of high quality are propagated from generation to generation
        
        Used to produce show animals (pets)
        
        show less variation
      - Out breeding
        
        Selective and controlled crossing among individuals from 2 different population, subspecies or closely realted species
        
        Offsprings = hybrids = have desirable characters of high quality compared to parents
        
        Shows more variation
        
        Usually used in production of crop plants with quality seeds or fruits.
- - - - Due to geographical isolation
        
        New species may rise
        
        Can't interbred
        
        Occurs rapidly
    - - A population forms a new species within the same geographical region
        
        Common in plant
        
        A change in ploidy
        
        A change in ecology
  - - - Prezygotic Barriers (before fertilization)
        
        Temporal
        
        Similar species that breed during different times of the day , cannot mix their gametes.
        
        Habitat
        
        Two species that live in different habitats within the same area
        
        Behavioral
        
        Many animal species exchange a distinctive series of signals before mating
        
        Gametic
        
        The gametes (egg and sperm) come into contact, but no fertilization takes place. Gametes may be unable to recognize one another in different species
        
        Mechanical
        
        Incompatible structures of their genital organ prevent succesful mating
      - Postzygotic Barriers (after fertilization )
        
        Hybrids Inviability
        
        reduces a hybrid's capacity to mature into a healthy, fit adult. The relatively low health of these hybrids relative to pure-breed individuals prevents gene flow between species.
        
        Hybrid sterility
        
        Hybrid animals may exhibit courtship behaviors incompatible with those of either parental species & as a result, they will not mate
        
        Hybrid breakdown
        
        In some cases when species cross-mate, the first generation hybrids are viable & fertille, but when these hybrids mate with one another or with either parent species, offspring of the next generation are feeble of sterile.
    - - Causes
        
        Founder Effect
        
        Random change in allele frequencies in a population during colonization
        
        Bottleneck Effect
        
        Results when a small number of individuals from a large population colonize a new area.
      - Random process by which allele frequencies in the population change over time.
        
        result in changes in allele frequency in a population from one generation to another & not by natural selection.
    - - Production of offsprings through interbreeding between 2 subspecies or 2 very closely related species
      - Hybrid usually infertile (2n)
      - Tetraploids (4n) are fertile
    - - A species gives rise to many new species in a short time
      - The gradual process of change from an ancestral species to form new species with each one occupying different ecological habitat and niche.
      - Eg. : Galapagos finches ( Darwin's Finches)