Causes of gene pool change

Question 1

Describe genetic equilibrium:

Answer 1

• No change in allele frequencies
• Population is not evolving or changing
• Also called Hardy-Weinberg equilibrium
• Evolution cannot occur at genetic equilibrium
• Microevolution - gradual change in allele frequencies

Question 2

Describe mutations:

Answer 2

• Change in the DNA of an individual
• Back mutation - reverse the effects of former mutations
• If the number of back mutations is equal to the number of mutations there are no net mutation
• Heritable mutations may diversify the gene pool

Question 3

Describe gene flow:

Answer 3

• Net movement of alleles from one population to another due to migration of individuals
• Increases genetic diversity in one population
• Reduces genetic diversity between populations

Question 4

Describe non-random mating:

Answer 4

• Random mating is probably uncommon due to preferred phenotypes
  
  • Example: animals might choose particular mates for certain traits
  • Inbreeding
    
    • Extreme example - some flowers self pollinate

Question 5

Describe genetic drift:

Answer 5

• If particular individuals do not breed, any unique alleles they have may be lost from the gene pool
• Change in allele frequencies due to chance events is called genetic drift
• Usually only occurs if populations size decreases relatively quickly

Question 6

Describe the founder effect:

Answer 6

• Founders - the individuals who form new populations
• Because founders are only a small number of individuals, they do not usually represent the entire gene pool
• Founders may not be typical of the whole population so frequency of rare alleles may increase
• Founder effect - gene pool change that occurs when a few individuals start a new, isolated population

Question 7

Describe the bottleneck effect:

Answer 7

• Gene pool change that results from rapid decreasing in population size
• Often seen in species driven to end of extinction
• Reduces genetic diversity, even if population regenerates

Question 8

Describe natural selection:

Answer 8

• Only process that leads directly to evolutionary adaptation
• Those animals with favourable traits survive
• Heterozygote advantage - when a harmful or lethal allele is actually beneficial in its heterozygous form
  
  • eg. sickle cell anemia