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10.3 U4 SPECIATION (How Poliploidy is related to Speciation? (Tetrahaploid…

- - - - Why does it happens?
        
        Occurs when reproductive isolating mechanisms prevent two breeding organisms from producing fertile and viable offspring (https://www.biology-online.org/dictionary/Viable)
  - - - The most famous example for this type of speciation is the galapagos finch; the species varies in terms of it's beak. For example, the galapagos finch that lives in island A has a big beak that enables them to capture insects easily while galapagos finch that lives in island B has thinner and longer beak that enables them to drink water from cactus plant without coming in contact with the cactus' sharp torns
    - - Sympatric speciation mostly occurs in plants species where parent plants produce offspring that are polyploid. The offspring live in the same environment as their parents but are reproductively isolated.
        
        However, this is an example of sympatric speciation in animals
  - - - Sympatric Speciation
        divergence of species within the same geographical location (i.e. without a physical barrier)
        
        may result from the reproductive isolation of two populations as a result of genetic abnormalities ---> prevents successful reproduction with any organism lacking the same error
        
        2.If meiotic cells fail to undergo cytokinesis, chromosomal number will double in the gamete (e.g. diploid instead of haploid) --->
        This will result in offspring that have additional sets of chromosomes (polyploidy)
        refer to *tetrahaploid
- - - - Phyletic Gradualism
        
        Definition
        
        Evolution occurs at a constant pace over a long period of time (due to the accumulation of mutations)
        
        Big changes (changes in the genes) results from many cumulative small changes (mutations)
        
        Important keys
        
        Evolution has a fairly constant rate
        
        New species arise by the gradual transformation of ancestral species
        
        The rate of evolution during the origin of new species is much like that at any other time.
      - Example
        
        Change in the horse's limbs from shorter to longer one that existed in modern horse (Reference: https://emmacookenvironmentaladaptations.weebly.com/pentadactly-limb.html)
        
        Change in size of hoof of the modern horse from larger to smaller one that existed in present day (Reference: https://www.tes.com/teaching-resource/evolution-of-the-horse-flash-cards-6325710)
      - Theory behind it: Charles Darwin (1809 - 1882), British naturalist
    - - Definition
        
        Punctuated Equilibrium
        
        Involves species with a shorter evolution
        
        ; individual species tend to show little or no change over a long period of geological time, and then enter a period of rapid change - which gives rise to new species
        
        a hypothesis devised to explain a pattern of change in the fossil record and how closely related species appear in nature
        
        pattern of speciation for punctuated equilibriums
        
        rapid natural selection in isolated populations
        
        genetic drift in small isolated populations
        
        Goldschmidt's "hopeful monster"
        
        sudden change due to breakdown of developmental homeostasis
      - Types
        
        Mutation
        
        Definition
        
        Chromosomal mutation in the number of chromosomes. Such mutations can produce sibling species which are morphologically similar but ecologically and reproductively isolated.
        
        Example
        
        The production of two sibling species of Drosophila pseudo-obscura and D. persimilis.
        
        Hybridization
        
        Definition
        
        This occurs when 2 different species mate and form offsprings a new species
        
        Example
        
        Raphanos brassica is the offspring of different species which are Brassica oleracea and Raphanos sativus
      - Theory behind it
        
        Speciation can be both abrupt and gradual when two isolated populations diverge
        
        1972 - proposed by Stephen Jay Gould and Niles Eldredge
        
        observed that fossil record gives a different picture for the evolution
        
        claimed that there were very long period of stasis (4-10 million years) involving little evolutionary change with occasional rapid formation of new species (as little as 5,000 to 50,000 years)
- - - - Speciation in Allium
      - The genus Allium is comprised of monocotyledonous flowering plants and includes onions, garlic, chives and leeks
      - In many of these species polyploidy has occurred, resulting in reproductively isolated populations with distinct phenotypes
      - Examples of polyploidy in Allium species includes:
      - Diploid (2n) = ~ 16 chromosomes (e.g. Allium cepa – garden onion)
      - Triploid (3n) = ~ 24 chromosomes (e.g. Allium carinatum – keeled garlic)
      - Tetraploid (4n) = ~ 32 chromosomes (e.g. Allium tuberosum – chinese chives)
    - - Poliploidy commonly occur in non-vertebrates and amphibians
        
        Example for non-vertebrates including flatworms, leeches and brine shrimp
        
        Example for amphibian including the Xenopus genus that contains 12 sets of chromosomes (dodecaploid)
      - Poli[loidy also occur in some fish and vertebrates
        
        As for fish, there are some fish with vertebrates that have as many as 400 chromosomes such as salmonids and cyprinids