Biology 12 Genetics and Evolution

Biology 12: Genetics and Evolutio Definitions Nucleotide Mutations Alleles: Alternative forms of a gene. Dominant allele only requires 1 copy in order to be expressed. Recessive allele requires two copies in order to be expressed. Point Mutations: Frameshift Mutations: Genotype: The combination of alleles one has at a given locus. Homozygous: Having two of the same allele. Heterozygous: Having two different alleles. Phenotype: The observable manifestation of a genotype. Dominance: Complete: Only one dominant allele. Codominance: More than one dominant allele. Incomplete: No dominant alleles; heterozygotes have intermediate phenotypes. Penetrance: The proportion of individuals carrying a particular allele that also express an associated phenotype. Expressivity: The varying phenotypic outcomes of a genotype. Genetic Leakage: Flow of genes between species via hybrid offspring. Genetic Drift: When the composition of the gene pool changes as a result of chance. Founder Effect: Bottlenecks that suddenly isolate a small population; inbreeding. Taxonomic Kingdom, phylum, class, order, family, genus, species. Rank: “King Phillip Came Over From Great Spain” The substituting of one nucleotide for another. Moving the 3 letter reading frame. Results: Silent: No effect on the protein. Missense: Replace one amino acid with another. Nonsense: A stop codon replaces an amino acid. Insertion/Deletion: Shift in the reading frame, leading to a change in all downstream amino acids. Chromosomal Mutations Much larger mutations, affecting whole segments of DNA. Results: Deletion: A large segment of DNA is lost. Duplication: A segment of DNA is copied multiple times. Inversion: A segment of DNA is reversed. Insertion: A segment of DNA is moved from one chromosome to another. Translocation: A segment of DNA is swapped with a segment of DNA from another chromosome. Analytical Techniques Punnett Squares: Monohybrid cross accounts for 1 gene. Dihybrid crosses account for two genes. Sex-linked cross is linked to the X chromosome. Recombination The likelihood of two alleles being separated during Frequency: crossing over in meiosis. Farther = !likely Mendel’s Laws Law of Segregation: An organism has two alleles for each gene, which segregate during Anaphase I. Because of this, gametes carry only one allele for a trait. Hardy-Weinberg If a population meets certain criteria (aimed at a lack Principle: of evolution), then the allele frequencies will remain constant. Law of Independent The inheritance of one allele does not influence the Assortment: probability of inheriting a given allele for a different trait (except for linked genes). Hardy-Weinberg P+q = 1 Equation: P2 + 2Pq+q2 =1 P=dominant-allele-freq q=recessive-allele-freq Evolution Experiments Natural Selection: The mechanism for evolution is natural selection. Experiments to support DNA as genetic material. Griffith: Demonstrated transformation. Heat-killed smooth (virulent) strain of bacteria still transformed rough strain into smooth. Avery-MacLeod- Degradation of DNA led to a cessation of bacterial McCarty: transformation. Degradation of proteins did not. Hershey-Chase: Confirmed DNA is the genetic material because only radiolabeled DNA could be found in bacteriophageinfected bacteria. Modern Synthesis Neo-Darwinism. Mutation and recombination are Model: mechanisms of variation. Differential reproduction. Inclusive Fitness: If a population meets certain criteria (aimed at a lack of evolution), then the allele frequencies will remain constant. Punctuated Considers evolution to be a very slow process with Equilibrium: intermittent rapid bursts of evolutionary activity. Mode of Natural Stabilizing Selection: Keeps phenotypes in a narrow Selection: range, excluding extremes. Directional Selection: Moves the average phenotype toward an extreme. Disruptive Selection: Moves toward two different phenotypes at the extremes, can lead to speciation. Adaptive Radiation: Rapid emergence of multiple species from a common ancestor, each has a niche. Isolation: Reproductively isolated from each other by pre- or postzygotic mechanisms. Divergent Evolution Parallel Evolution Convergent Evolution Molecular Clock The degree of difference in the genome between Model: two species is related to the amount of time since the two species broke off from a common ancestor.