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Welcome to AP BiologySaturday Study Session
Macroevolution
Question 1
cClue: prior to the formation of K‐T
boundary
Fossils show that speciation and extinction have occurred throughout the Earth’s history
Tota
l ext
inct
ion
rate
(fam
ilies
per
mill
ion
year
s):
Time (millions of years ago)
Num
ber o
f fam
ilies
:
CenozoicMesozoicPaleozoicE O S D C P Tr J
542
0
488 444 416 359 299 251 200 145
EraPeriod
5
C P N65.5
0
0
200
100
300
400
500
600
700
800
15
10
20
Extinction rates are high at times of ecological stress
Question 2
bClue: conditions were sufficient
Scientific evidence supports several models about the origin of life on Earth
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Question 3
dClue: DNA replicates with fewer
errors
Question 4
bClue: oxygen accumulated prior to
evolution of eukaryotes
Origin of Life Timeline
Accumulation of oxygen in the atmosphere (2.5 bya)
Question 5
cClue: accumulate features rapidly, then
change little
Speciation Rates Can Vary Question 6
bClue: point mutation
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Gene duplications may provide new phenotypes Question 7
aClue: islands
Adaptive Radiation Example Math Grid In 1
The correct answer: 17,190 years
Solution:• Step 1: 100% ÷ 8 = 12.5%• Step 2: Time 0 = 100% = 0 years
First half‐life = 50% = 5,730 yearsSecond half‐life = 25% = 5,730 yearsThird half‐life = 12.5% = 5,730 years
Adds up to: 17,190 years
Half‐life• time required for the radioactive material to decrease by one half Math Grid In 2
The correct answer: 14
Solution:12 + 16 = 28 (diploid)28/2 = 14 (haploid)
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Allopolyploidy
Species B2n = 6
Species A2n = 4
Normal gameten = 3
Normal gameten = 3
2n = 10
Unreduced gametewith 4 chromosomes
Unreduced gametewith 7 chromosomes
Hybrid with7 chromosomes
Viable fertile hybrid(allopolyploid)
Meiotic error;chromosomenumber notreduced from2n to n
Autopolyploidy
Failure of cell division in a cell of a growing diploid plant after chromosome duplication gives rise to a tetraploid branch or other tissue.
Gametes produced by flowers on this tetraploid branch are diploid.
Offspring with tetraploid karyo‐types may be viable and fertile—a new biological species.
2n = 64n = 12 4n
2n
Short Free Response 14 points possible
Description of kind of data (1 pt each)
Explanation (1 pt each)
Ability to produce viable seeds/offspring in nature
Consistent with definition of biological species
Ability to cross‐pollinate Consistent with definition of biological species
Production of fertile offspring Consistent with definition of biological species
Comparison of sequences of DNA/chromosomes or other conserved molecules
Similarity supports single species
Fertile hybrid populations found living between the two other populations of plants
Consistent with definition of biological species
For each kind of data, must include description and explanation.
Short Free Response 22 points possible
Mechanisms that lead to the development of separate species from a common ancestor (1 point each)
• Allopatric speciation takes place when a population of one species becomes physically separated by some geographic barrier such as a river, mountain range, etc. Long‐term isolation of two populations eventually leads to reproductive isolation.
• Sympatric speciation happens when new species arise as a result of reproductive isolation within the population range ‐ for example, because of polyploidy or switching mating behaviors (fruit flies going from hawthorn to apple to lay eggs). Eventually the two populations are unable to interbreed.
• Reproductive isolation by prezygotic barriers such as habitat, temporal, behavioral, mechanical or gametic incompatibility.
• Reproductive isolation by postzygotic barriers (e.g., reduced hybrid viability or fertility) leads to speciation.
Modes of Speciation
Allopatric speciation Sympatric speciation
Prezygotic and Postzygotic Isolating Mechanisms