Evolution of Populations

1
Chapter 16

• Evolution of Populations

2
What Darwin Did Not Know

• He did not know how traits were passed on from
  one generation to the next.
  
• He did not know how variations appeared.

3
Genetic Variation

• Remember genes have at least 2 forms (alleles)
• Sources of genetic variation
• 1. Mutation change in a sequence of DNA
• 2. Gene Shuffling genes move about during the
  production of gametes (sex cells)

4
Variation and Gene Pools

• Remember a population is a group of individuals
  of the same species that interbreed.
  
• Because they interbreed, the group of genes is
  called the gene pool
  
• Gene pool all the genes in a population

5
Relative Frequency

• The number of times that the allele occurs in a
  gene pool
  
• Expressed in percentage
• Ex. Mouse population relative frequency of the
  dominant allele (black fur) is 40
  
• In genetic terms evolution is any change in
  the relative frequency of alleles in a population.

6
Single-Gene and Polygenic Traits

• The number of phenotypes produced for a given
  trait depends on how many genes control the
  trait
  
• Single-Gene one gene, two alleles
• Ex. Widows Peak
• Polygenic Traits traits controlled by two or
  more genes
  
• Ex. Height

7
16-3 Speciation

• Speciation formation of new species
• As new species evolve, populations become
  reproductively isolated from each other
  
• Reproductive isolation

8
Other Types of Isolation

• Geographic Isolation two populations are
  separated by geographic barriers
  
• Ex. Rivers, Mountains
• Abert squirrel Kaibab squirrel Grand Canyon
• Temporal Isolation two or more species
  reproduce at different times
  
• Ex. 3 species of orchids release pollen on a
  different day

9
Galapagos Finches

• Darwin thought they were completely different
  types of birds.
  
• Natural selection shaped the beaks of different
  bird populations as they adapted to eat different
  foods.
  
• Since Darwin, the Grants have studied the finch
  populations for years.

10
Galapagos Finches

• Grants work showed that finch beak size can be
  changed by natural selection.
  
• Birds with different sized beaks had different
  chances of survival during a drought.
  
• Scarce food sources birds with largest beaks
  survive
  
• Next generation birds with larger beaks

11
Process of Speciation

• 1. Founders Arrive
• 2. Geographic Isolation
• 3. Changes in the Gene Pool
• 4. Reproductive Isolation
• 5. Ecological Competition
• 6. Continued Evolution