Ch. 16, Evolution of Populations

1
Ch. 16, Evolution of Populations

• Why are we all so different?
• Variation in populations is the raw material for
  evolution
• 2 main sources of variation
• Mutations any change in a sequence of DNA,
  some are harmful, some are beneficial and some
  dont have any effect at all
• Gene shuffling mixing of genes due to random
  mating
• 23 pairs of chromosomes can produce 8.4 million
  different combinations of genes
• Crossing over during Meiosis

2
Variation and Gene Pools

• Genetic variation is studied in POPULATIONS, not
  individuals
• Members of a population share a Gene Pool
• Gene pool consists of all genes, including all
  the different alleles that are present in a
  population
• Why?
• They descended from a common ancestor
• Relative frequency of an allele number of times
  an allele occurs in a gene pool
• So, evolution is any change in the relative
  frequency of alleles in a population

3

• Genetic Drift random change in allele
  frequencies that occurs in small populations
• In small populations, individuals that carry a a
  particular allele may leave more descendants than
  other individuals, jus by chance. Over time, a
  series of chance occurrences of this type can
  cause an allele to become common in a population

4

• Genetic Equilibrium allele frequencies remain
  constant
• Five conditions required to maintain genetic
  equilibrium
• Random mating
• The population must be very large
• No movement into or out of the population
• No mutations
• No natural selection
• This is the Hardy-Weinberg principle