Different species are reproductively isolated

1
Ch 24 Origin of Species

• Different species are reproductively isolated
• Micro-evolution leads to micro-evolution

2
What keeps species separate?

• Prezygotoc barriers ( prevent zygote formation)
• temporal isolation different mating times
• behavioral isolation songs, signals, rituals
• habitat isolation ( I cant reach you )
• mechanical isolation some flowers are adapted
  for special pollinators
• gamete isolation - Incompatible gametes

3

• Postzygotic barriers hybrid zygote doesnt
  develop due to
• hybrid sterilty
• loss of vigor
• loss of viability

4
Modes of speciation macro-evolution

• Allopatric speciation - occurs when a gene pool
  is divided by geographic isolation (different
  lands ) - happens most rapidly on islands with
  small founding populations
• Sympatric speciation speciation occurs in
  geographically overlapping populations
• ( same land ) due to some type of reproductive
  barrier

5

• Adaptive radiation ancestral specie moves into
  diverse envrionments

Hawaiian birds
6
Polyploidy in plants works( but not in animals)

• Polyploidy having more than 2 sets of
  chromosomes/ cell ( more than 2N )
• 4N, 8N - mistakes in meiosis result in 4N
  gametes. Self fertilization 8N
• Some plants do well with this ( corn, wheat
  potato)

7
Punctuated Equilibrium

• Evolution appears to proceed in bursts at times.
  Transitional fossils are not abundant.
• Allopatric speciation may account for this
• Most changes in a specie occur when the specie
  first buds from parent specie. Then the specie
  stabilizes for a long period. This would account
  for minimal transitional evidence.

8
evo-devo How might changes in developmental
patterns have affected evolution?

• Hox genes control positions of parts
• Hox genes regulate body areas. Over or under
  expression of a gene affects its effect ?
• Changes in timing of developmental events
  heterochrony.. When the gene turns on or off