Evolution of Populations

• quantitative characters


  heritable variation result from the influence of two or more genes on a single phenotype
• gene variability


  genetic variation at the whole-genome level
• nucleotide variability


  molecular level of DNA
• average heterozygous


  average percentage of the loci that are heterozygous
• identifying heterozygous loci is determined by surveying the protein products of genes using gel electrophoresis
• gel electrophoresis cannot detect silent mutations
• to detect silent mutations PCR-based methods and restriction fragment analysis is used
• geographic variation 


  differences in genetic composition of separate populations
• karyotypes


  an individuals complete set of chromosomes
• patterns of fused chromosomes differ from one population to another
• cline


  graded change in a character along a geographic axis
• some clines are produced by a gradiation in an environmental variable
• clines are the result of natural selection
• many genetic variations can be produced in short periods of time in fast reproducing organisms
• mutations occur in somatic cells and are lost when the individual dies
• somatic cells 


  diploid cells, all the other cells in the body par the sperm and egg
• mutations can quickly bring about genetic variation
• sexual reproduction has most of genetic variation from the combination of the alleles
• sexual reproduction diversity

  crossing over, independent assortment, random fertilization
• only one allele in a loci exists in a population then allele if fixed
• Hardy-Weinburg principle

  q2 + 2pq + q2 = 1
• assumptions for HW

  no mutations, random mating, no selection, large population, no gene flow
• natural selection


  individuals within a population exhibit variation in their heritable traits which are better suited for their environment allowing them to produce offspring and pass on said traits
• natural selection can cause adaptive evolution
• adaptive evolution


  evolution that results in a better match between organisms and their environment
• genetic drift


  fluctuations of allele frequencies unpredictably within a small population from one generation to the next
• bottlenecking and founder effect are genetic drift
• founder effect


  individuals become isolated from a larger population and develop a smaller population whose gene pool differs from the source population
• bottleneck effect


  a sudden change in environment drastically reduces the population
• bottlenecked populations will recover in size but will have reduced genetic variation
• genetic drift leads to shifting of allele frequencies and loss of genetic variation
• genetic drift can can fix harmful alleles
• allele frequency can also change by gene flow
• transfer of alleles that improve the ability of population to adapt to the local conditions
• humans are leading to fewer genetic differences between populations due to migration
• neutral variation


  differences in DNA sequences that do not confer a selective advantage or disadvantage
• balancing selection


  natural selection maintains two or more forms in a population
• heterozygote advantage


  individuals who are heterozygous at a particular locus gave greater fitness than the homozygous
• frequency-dependant selection


  fitness of phenotype depends on how common it is in the population