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Topic 10: Genetics and Evolution, (a. unlinked genes are on different…

- - - - Morgans experiments with fruit flies demonstrated that linked genes are not independently assorted.
      - When cross-breeding red-eyed types with white-eyed eyes, a clear sex bias was identified in phenotypic distribution:
        a female offspring of a RED EYED male were RED EYED
        all male offspring of WHITE EYED FEMALE were WHITE EYED
      - This was due to the gene for eye color being located on a sex chromosome.
        1) the alleles for these traits were located on a shared chromosome and hence did not independtly assort
        2) linked alleles could be uncoupled via recombination in crossing over to create alterantive phenotypic combinations.
    - - Recombinants occur as a result of crossing over of genetic material during prophase I of meiosis.
        
        If linked genes become separated by chiasma there will be an exchange of alleles between non-sister chromatids.
        
        the frequency of recombinat phenotype will be lower than the phenotype of non-recombinant phenotypes: because crossing over is a random process and chiasmata do not form at the same locations in every division.
      - The frequency of recombinant phenotypes will be dependent on the distance between linked genes.
        
        Recombiantion frequency between two linked genes will be greater when the genes are further apart on a shared chromosome because there are more possible locations where a chiasma could form between genes.
        
        if observed frequencies do not conform to those expected in an unlinked dihybrid cross it suggests that:
        
        genes are linked and not indepedntly assorted
      - Chi-squared tests are used to determine whether the difference between an observed and expected frequency distribution is statistically significant.
        
        Chi-squared = sum of ((O - E)^2 / E)
        
        Where,
        
        O is the observed frequency.
        
        E is the expected frequency.
        
        https://dl.ibdocs.re/IB%20QUESTIONBANKS/5.%20Fifth%20Edition%20-%20TOPIC/questionbank.ibo.org/en/teachers/00000/questionbanks/43-dp-biology/questions/875519.html
        
        expc freq is total from one row and total from one clumn (one charactersitc) and divide by total of all
        
        If the Chi-Square value does not exceed the critical value (e.g. p=0.05 (can be 0.059 too) then the null hypothesis will be accepted i.e. the data does follow the hypothetical pattern. If it does exceed the critical value, the null hypothesis must be rejected.
    - - Variation in phenotypes for a particular characteristic can be either discrete or continous:
        
        Monogenic traits are those controlled by a single gene loci. these tend to exhibit discrete variation, with individuals expressing a certain phenotype.
        
        Polygenic traits are those controlled by more than one gene loci, these exhibit continous variation, with an individuals phenotype existing somewehre along a spectrum of potential phenotypes.
        
        increasing the number of gene loci responsible for a specfici characteristic increases the number of potnetial phenotypes.
      - Maize Grain Colour: polygenic trait controlled by 3 gene loci, the grain color can range from red to white.
        this pattern of inheritance shows continous variation.
      - Polygenic traits such as human height may also be influenced by environmental factors.
        
        The added effect of environmetnal pressures functions to increase the variation for a particular trait.
        
        human height is a polygenic trait infleunced by the environment.
        diet/disease are environemntal factors that may infleunce an individuals height.
        another polygenic trait is human skin color as it shows continous variation
- - - - GRADUALISM
        b. gradualism suggests that evolution occurs over a long time;
        c. gradualism changes are slow/steady over time;
        d. gradualism would occur when there is little change in the environment;
      - PUNCTUATED EQUILIBRIUM
        a. long periods of stability;
        b. environmental change / sudden change;
        c. leads to rapid speciation/evolution;
    - - polyploidy more common in plants and is desriable for farmers as it allwos for the production of seedless fruits
      - The genus allium shows speciation due to polyploidy:
        The genus Allium is comprised of monocotyledonous flowering plants (onions, garlic)
        In many of these species polyploidy has occurred, resulting in reproductively isolated populations with distinct phenotypes, producing infertile offsprings.