AP Biology

MacroevolutionPart 2

Modes of Speciation

Allopatric speciation Sympatric speciation

Geographic Range of west coast salamanders (A ring species)

Galapagos Islands

Galapagos Islands close up

Darwin’s Galapagos Island finches

Modes of Speciation

Allopatric speciation Sympatric speciation

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

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

Stephen Jay Gould

.

Time

Gradualism model Punctuated equilibrium model

Mass extinctions over time

Millions of years ago600 500 400 300 200 100

Permian massextinction

100

80

60

40

20

0

Extinction rate

Cretaceousmass extinction

02,500

2,000

1,500

1,000

500

0

Neo

gene

Prot

eroz

oic

eon

Cam

bria

n

Ord

ovic

ian

Silu

rian

Dev

onia

n

Carb

onife

rous

Perm

ian

Tria

ssic

Jura

ssic

Cret

aceo

us

Pale

ogen

e

Paleozoic MesozoicCeno-zoic

Num

ber o f families (

)Extin

ction

rate

()

Number oftaxonomic

families

Snowball Earth

PangaeaBy about 10 million yearsago, Earth’s youngestmajor mountain range,the Himalayas, formedas a result of India’scollision with Eurasiaduring the Cenozoic.The continents continueto drift today.

By the end of theMesozoic, Laurasiaand Gondwanaseparated into thepresent-day continents.

By the mid-MesozoicPangaea split intonorthern (Laurasia)and southern(Gondwana)landmasses.

At the end of thePaleozoic, all ofEarth’s landmasseswere joined in thesupercontinentPangaea.

0

65.5

135

251

Mill

ions

of y

ears

ago

Ceno

zoic

Mes

ozoi

cPa

leoz

oic

North America

Eurasia

AfricaIndiaSouth

America Madagascar

Australia

Antarctica

Laurasia

Gondwana

Pangaea

Asteroid Impact

NORTHAMERICA

ChicxulubcraterYucatán

Peninsula

Example of Descent with Modification and Natural Selection

Evolution of the eye

Complex camera-type eye

Pinhole camera-type eye Eye with primitive lens

Patch of pigmented cells Eyecup

Pigmented cells(photoreceptors)

Epithelium

Nerve fibers

Fluid-filled cavity

Epithelium

Pigmentedlayer (retina)

Opticnerve

Pigmentedcells

Nerve fibers

CorneaCellularfluid(lens)

Optic nerve

Cornea

Lens

Optic nerve

Retina