genetic diversity and natural selection

• what is an allele

  Different forms of a gene
• what is genetic diversity

  The total number of different alleles in a species or population
• what is a population


  a group of individuals of the same species living in the same area at the same time
• how can genetic diversity within a population be increased (2 reasons)

  1. mutations in DNA (forms new alleles)

  2. gene flow - when individuals from other populations migrate and reproduce in the new population introducing new alleles
• what ia a genetic bottleneck

  an event that causes a large reduction in the population
• how does a genetic bottleneck reduce genetic diversity

  - reduces the number of different alleles in the gene pool

  - when the survivors reproduce all offspring have their alleles so the population grown but all genetically similar
• what is the founder effect

  when a few individuals become isolated from a larger population, and their gene pool differs from that source population

  - could have more of a rare allele- could lead to more genetic disease

  - could have more of an advantageous allele
• how can random occurring mutations be beneficial to an organism

  e.g. may produce a protein better than original

  gives the organism a higher chance of survival
• describe the process of natural selection

  1. genetic diversity within population (range of alleles)

  2. an environmental change occurs/selection pressures/competition (abiotic or biotic)

  3. some individuals have advantageous alleles due to random mutation - more likely to survive, reproduce and pass on advantageous allele

  4. individuals without advantageous allele die out

  5. over time the frequency of the advantageous allele in the gene pool will increase
• natural selection means species are better adapted to environment

  what are the 3 types of adaptation

  behavioural

  anatomical

  physiological
• what is meant by behavioural adaptations

  the way an organism acts to increase its chance of survival

  e.g. animals(possums) may 'play dead' is they feel threatened by a predator
• what is meant by anatomical adaptations

  structural features of an organisms body that increases chance of survival

  e.g. whales have thick layer of blubber to keep warm in cold conditions
• what is meant by physiological adaptations


  processes inside an organisms body that increase its chance of survival

  e.g. brown bears hibernate - lower their rate of metabolism to conserve energy, don't have to look for food when it is scarce
• what are the 3 types of natural selection

  directional, stabilizing, disruptive
• what is directional selection


  selection pressure against one extreme of trait
• directional selection graph

  if left is disadvantageous allele and right is advantageous there is movement toward advantageous

  mean shifts, same level of variation

  
• what is stabilising selection

  selection pressures against both extremes of trait
• stabilising selection graph

  does not change mean, variance decreases

  
• what is disruptive selection

  selection pressure against midpoint of trait
• disruptive selection graph

  leads to speciation

  
• how does selection effect the avergage of a phenotype

  e.g. natural selection causes longer fur habits to survive cold winters, reproduce and pass on allele, overtime longer fur becomes more common in population so average fur length increases