Chemistry of Macromolecules

1
(No Transcript)
2
Speciation

• IB HL Biology 2

3
Evolution is

• The change in genetic (allelic) frequencies in a
  populations gene pool that takes place over time.

4
Microevolution

• Minor changes that lead to the appearance but
  closely related species.

5
What is a species, then?

• Organisms of the same group that can interbreed
  and produce fertile offspring.

6
Biological species concept

• A population whose members have the potential to
  interbreed with one another in nature to produce
  viable, fertile offspring, but who cannot produce
  viable, fertile offspring with members of other
  species

7
What does this mean?

• Reproductive isolation is the key once similar
  organisms are no longer able to interbreed in
  nature, they are considered to be another species.

8
Reproductive Isolation

• Barriers that prevent two species from producing
  viable fertile hybrids

9
Pre-zygotic barriers

• Do not allow species to mate
• Does not allow fertilization of eggs

10
Habitat Isolation

• Species living in different locations may never
  meet and thus will never mate.

11
Behavioral Isolation

• If mating behaviors are dissimilar among species,
  mating may not occur
• Unique behaviors allow own species recognition

12
Temporal Isolation

• When species mate at different times of year and
  are not able to breed with one another

13
Mechanical Isolation

• The reproductive organs of two species are
  incompatible

14
Gametic Isolation

• Gametes of 2 species may not meet due to chemical
  barriers preventing survival of sperm
• Important to aquatic species

15
Polyploidy

• Having more than a diploid chromosome number
• Can be the result of nondisjunction mutation
• Can be the result of getting chromosomes from
  another member of the same species
  autopolyploidy

16
Polyploidy

• Can happen through unison of chromosomes from two
  different species allopolyploidy
• In plants-not uncommon
• In animals-does not occur

17
Postzygotic Barriers

• Barriers that prevent the hybrid zygote from
  becoming an adult.

18
Reduced hybrid viability

• Genetic incompatibility may force miscarriage of
  hybrid embryo

19
Reduced hybrid fertility

• Adult hybrid organisms can be sterile

20
Hybrid Breakdown

• 1st generation hybrids are fertile but subsequent
  generations are not

21
Limitations to the BSC

• Does not account for asexually reproducing
  organisms, like bacteria
• Does not account for interbreeding that may have
  happened in fossil species

22
Mode of speciation Allopatric

• Two species are separated by a physical barrier
  that causes them to be isolated

23
Mode of speciation sympatric

• New species arise within parent population
• Geographically overlapping populations
• Can occur due to polyploidy (in plants)

24
Adaptive Radiation

• Rapid speciation of a species to fill niches
• Results in great diversity

25
Genetic Change

• Adaptive divergence 2 parts of population adapt
  to different environments
• Each accumulates different gene pools
• Reproductive barriers develop
• Usually secondary to change in gene pool
• May be side effect of sexual selection

26
Gradualism vs. Punctuated equilibrium

• Gradual change over time vs. long periods of
  stasis punctuated by rapid changes

27
(No Transcript)