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3/23/2016 1 Welcome to AP Biology Saturday Study Session Macroevolution Question 1 c Clue: prior to the formation of KT boundary Fossils show that speciation and extinction have occurred throughout the Earth’s history Total extinction rate (families per million years): Time (millions of years ago) Number of families: Cenozoic Mesozoic Paleozoic E O S D C P Tr J 542 0 488 444 416 359 299 251 200 145 Era Period 5 C P N 65.5 0 0 200 100 300 400 500 600 700 800 15 10 20 Extinction rates are high at times of ecological stress Question 2 b Clue: conditions were sufficient Scientific evidence supports several models about the origin of life on Earth 
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Page 1: 1 AP Clue: K T Macroevolutionslhsapbiology.weebly.com/uploads/5/8/8/8/58880189/09-ap...Macroevolution Question 1 c Clue: prior to the formation of K ‐T boundary Fossils show that

3/23/2016

1

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 

Page 2: 1 AP Clue: K T Macroevolutionslhsapbiology.weebly.com/uploads/5/8/8/8/58880189/09-ap...Macroevolution Question 1 c Clue: prior to the formation of K ‐T boundary Fossils show that

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2

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)

Page 4: 1 AP Clue: K T Macroevolutionslhsapbiology.weebly.com/uploads/5/8/8/8/58880189/09-ap...Macroevolution Question 1 c Clue: prior to the formation of K ‐T boundary Fossils show that

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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

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