Genetics and Evolution

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  • Created by: jessica
  • Created on: 15-04-13 12:20
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  • Genetics and Evolution
    • Inversions
      • segment of chromosome is cut out, flipped and reinserted
      • two types of inversion, paracentric and pericentric
        • paracentric is when the centromere is outside the inversion
          • can lead to deletion products
        • pericentric when the inversion spans the centromere
          • can lead to duplication
    • INhertied diseases
      • often due to recessive alleles as they can create reservoirs
      • e.g. huntington's chorea is autosomal dominant
      • e.g. fibrocystic disease is an autosomal recessive gene
    • Variation at chromosomal level
      • polymorphism for chromosome number and morphology includes extra chromosomes, reciprocal translocations, inversions
    • Mendel
      • his conclusions were that characters are controlled by pairs of alleles which can be dominant or recessive. alleles segregate at random
      • created law of independent assortment and law of segregation
    • Complementation
      • production of wildtype phenotype when two haploid genomes bearing different recessive mutations are united in the same cell
      • Complementation test
        • intercrossing two homozygous individiuals for different recessive mutations, observing whether the progeny have wild type phenotype
      • complementation group when two or more groups control a phenotype
      • used to classify mutations as alleles of the same or of different genes
    • Sex linked inheritance
      • Morgan found white eyed male flies amongst a red eyed fly population
      • examples of human sex linked inheritance are haemophilia, DMD
      • X linked recessive disorders are when males show the phenotype
      • X linked dominant disorders also occur
    • The nature of variation
      • complex gene traits
        • phenotype can be expressed in one of 3 ways, continuous, meristic and threshold
          • continuous
            • polygenic plus environmental determination, no discrete classes of phenotype, no discontinuities
          • meristic
            • polygenic plus environmental determination, underlying distribution is continuous, phenotype only expressed in whole units
          • threshold
            • polygenic and environmental distribution with few phenotypes, have underlying predisposition for the trait
    • Pedigree patterns
      • used to track inheritance in humands and livestock
      • four main patterns of inheritance are autosomal dominant, autosomal recessive, X lionked recessive, Y linked dominant
        • autosomal recessive disorders appear in progeny of unaffected parents and the affected progeny are both male and female
        • autosomal dominant disorders have phenotypes that appear in every generation of the pedigree and there is equal representation of both sexes
    • Linkage and recombination
      • recombination when homologous chromosomes can exchange sections
        • big physical distance means more likely to cross over
        • crossing over occurs at prophase 1 of meiosis
        • multiple cross overs occur with map distance greater than 10cM
    • gene interactions
      • interactions between alleles within a single gene include complete dominance, incomplete dominance co-dominance
        • complete dominance is the base default Mendelan setting
        • incomplete dominance is when the the heterozygous phenotype is intermediate to the two parent phenotypes and the parents are homozygous
        • codominance is when the heterozygote displays the phenotype of both homozygotes
      • epistasis is interactions between genes
        • phenotypic effects arise when 2 or more genes interact and genes are no longer independent of each other
        • changes F2 phenotypic ratios, will be less than 4 phenotypes
      • penetrance and expressivity are interactions between genes and the environment
        • penetrance is the proportion of individuals carrying a particular allele that expresses the associated phenotype
        • expressivity measures the extent to which a genotype exhbitis its phenotype
    • genetic mapping
      • relies on DNA polymorphisms rather than "real" genes
      • uses various DNA polymorphisms including RFLP, VNTR, STR, SNP
    • protein polymorphisms
      • different types of protein polymorphisms, immunologic and amino acid sequence
      • immunologic polymorphism when the 40 different specificities for antigens on human red blood cells
      • amino acid polymorphism is when amino acid substitutions may directly replace a charged or noncharged substitution near a charged amino acid
    • Phenotypic variance is determined by genes and environment
      • Vp=Vg + Ve
        • Vg valculated by Va + Vd
          • Va=additive variance, Vd=dominance variance
            • The 2 alleles can have dominance interactions and either allele can show dominance
            • additive variance when each allele in a polygenic system contributes to the observed phenotype
              • positive additive will increase the strength of the phenotype
              • negative additive will decrease the strength of the phenotype
    • Heritability
      • measure of the influence that genes have on a phenotype
      • allows the measure of contribution of genetic components
      • 2 types of heritability broad and narrow
        • equation for broad heritability is H2 = Vg/Vp
        • equation for narrow is h2=Va/Vp
          • narrow is more specific
      • is the property of variation within one population in one environment at one time, are ratios
    • Hardy-Weinberg equilibrium
      • sexual reproduction does not cause a constant reduction in genetic variation in each generation, so amount of variation remains constant in the absence of other driving forces
      • uses the assumption that mating is random and there are no selection pressures
      • equation is p+q=1 and p2+2pq+q2=1
      • p is the dominant allele and q is the recessive allele
    • genetic structure of populations
      • population genetics applies to the genetic principles to entire populations of organisms
      • aubpopulation is a population unit within a larger population
      • Mendelian population is the natural interbreeding unit of sexually reproducing plants or animals sharing a common gene pool
      • gene pool is all the alleles in a population
      • genotype frequency is the proportion of individuals in a population with a specific genotype
      • allele frequency is when the proportion of each specific allele in a population
        • allele and genotype frequencies remain the same if there is random mating, no mutation, mo migration, no selection, no random genetic drift
          • genotype frequency is the proportion of individuals in a population with a specific genotype
    • Inbreeding and genetic burden
      • inbreeding when there is a higher than chance related mating
        • combines alleles of common ancestory, promotes homozygosity
        • effects are more pronounced in small isolated populations
        • promotes the incidence of genetic abnormalities
      • outbreeding when there is lower than chance related mating
      • assortative mating is when there are more traits in common
      • disassortative mating is when more of the traits are dissimilar
    • Forces of evolutionary change
      • mutation
        • raw material of evolution, genes and chromosomes mutate
          • chromosome mutations are deletions, translocations, nondisjunction and inversions
          • gene mutations are point, substitutions, inversions/deletions and frame shift
      • selection
        • directional, diversifying, stabilizing
          • diversifying can lead to speciation
        • most likely cause of rapid changes in allele frequency
        • selective advantage depends on relative fitness of genotypes
      • migration
        • movement of alleles between populations
      • genetic drift
        • chance fluctuations in allele fequency due to random sampling of gametes
    • Neutral mutations and molceular evolution
      • mutations can have three effects on fitness-deleterious, increase, neutral
        • neutral has no effect on fitness
      • rate of neutral replacement = 2Nu x 1/(2N) = u
    • Speciation
      • new species defined when it can no longer mate with its former self
      • Allopatric speciation when physical isolation is involved
      • Sympatric speciation is when populations are reproductively isolated but may not be physically isolated
      • pre mating isolation mechanisms include ecological, seasonal/temporal, sexual, mechanical, isolation by different populations
      • postmating isolation mechanisms include gametic isolation, hybrid unviability, hybrid sterility, hybrid breakdown
    • Phylogeny and Systematics
      • phlogeny is a branching diagram showing relationships between species based on their shared common ancestor
      • cladogenesis is the splitting of evolutionary linkages to form clades
      • anagenesis is the accumulation of phenotypic changes within a lineage
      • synapomorphies are traits mapped onto a phylogenetic map
      • monophlyetic group includes an ancestor and all of its descendants
      • paraphyletic group includes an ancestor and some but not all of its descendants
      • polyphyletic group includes two convergent descendants but dont shar a common ancestor
      • convergence is the acquisition of the same biological trait in different lineages
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