gen bio

• Biological evolution


  Descent with modification
• Biological evolution is not simply a matter of change over time
• Fundamental to the process of evolution

  • Genetic variation upon which selective forces can act
  • Descent and the genetic differences that are heritable and passed on to the next generation
• Mechanisms of evolution


  • Mutation
  • Migration (gene flow)
  • Genetic drift
  • Natural selection
• Mutation


  A change in DNA, the hereditary material of life
• Sources of genetic variation

  • Mutations
  • Gene flow
  • Sex (genetic shuffling)
• Mutations are random
• Somatic mutations


  Occur in non-reproductive cells and won't be passed onto offspring
• Germ line mutations


  Occur in reproductive cells like eggs and sperm and can be passed on to offspring
• Effects of a single germ line mutation


  • No change in phenotype
  • Small change in phenotype
  • Big change in phenotype
• Lethals


  Mutations that cause the death of an organism
• Reasons for mutations


  • DNA fails to copy accurately
  • External influences can create mutations
• Sex and genetic shuffling

  Sex can introduce new gene combinations into a population and is an important source of genetic variation
• Gene flow (migration)


  Any movement of individuals and/or the genetic material they carry from one population to another
• Genetic shuffling


  When organisms reproduce sexually, new combinations of genes are brought together
• Genetic shuffling


  • Bushy eyebrows and big nose (from mom's and dad's genes)
• Genetic shuffling is important for evolution as it can introduce new combinations of genes every generation, but can also break up "good" combinations
• Gene flow


  Any movement of individuals, and/or the genetic material they carry, from one population to another
• Gene flow


  • Pollen being blown to a new destination
  • People moving to new cities or countries
• If gene versions are carried to a population where those gene versions previously did not exist, gene flow can be a very important source of genetic variation
• Genetic drift


  Random fluctuations in the frequency of appearance of a gene, usually in a small population
• Genetic drift can cause gene variants to disappear completely, thereby reducing genetic variability
• Genetic drift is a stochastic process, a random event that happens by chance in nature that influences or changes allele frequency within a population as a result of sampling error from generation to generation
• Population bottleneck


  A sudden sharp decline in a population's size typically due to environmental factors
• Founder effect


  The loss of genetic variation that occurs when a new population is established by a small number of individuals that are cleaved from a larger population
• Genetic drift


  1. Generation 1: Frequency of alleles is the same

  2. Generation 2: Most individuals die due to catastrophic event

  3. Generation 3: Surviving population has much less genetic variability

  4. Generation 4: Population expands but is no longer genetically representative of original
• Genetic drift affects the genetic makeup of the population but, unlike natural selection, through an entirely random process
• Natural selection


  • Populations of organisms are subjected to the environment
  • The fittest creatures are more likely to survive and pass their genes to their offspring, producing a population that is better adapted to the environment
  • The genes of less-fit individuals are less likely to be passed on to the next generation
• Natural selection


  • Green beetles are easier for birds to spot and eat, so brown beetles are more likely to survive and reproduce
• Natural selection and genetic drift cannot operate unless there is genetic variation - that is, unless some individuals are genetically different from others
• Natural selection


  • There is variation in traits
  • There is differential reproduction
  • There is heredity
• If you have variation, differential reproduction, and heredity, you will have evolution by natural selection as an outcome
• Beetles


  • Green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do
• There is heredity
• Surviving brown beetles


  Have brown baby beetles because this trait has a genetic basis
• Natural selection


  1. Differential reproduction

  2. Heredity

  3. End result
• Differential reproduction


  Since the environment can't support unlimited population growth, not all individuals get to reproduce to their full potential
• Heredity


  The surviving brown beetles have brown baby beetles because this trait has a genetic basis
• End result


  The more advantageous trait, brown coloration, which allows the beetle to have more offspring, becomes more common in the population. If this process continues, eventually, all individuals in the population will be brown
• Natural Selection leads to an evolutionary change when some individuals with certain traits in a population have a higher survival and reproductive rate than others and pass on these inheritable genetic features to their offspring