Semester 2, Day 12
Fossil Evidence of Evolution
Homework Due
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Cornell Notes on 14.3 and 14.4
Questions:
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14.3 #1-3
14.4 #1-5
Chapter 14 Assessment #3, 4, 6, 10-14, 16, 20, 22a, 22c
Isolation and Speciation
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Speciation: process of creating a new species
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Isolation: a way in which to prevent species from breeding
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Recall: species = group of similar organisms capable of
producing fertile offspring!
If population B can no longer mate with population A, but
CAN produce offspring within population B, then it is a new
species.
Over time, isolation results in speciation
Barrier: anything that separates species from each other
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Reproductive: prevents them from breeding
Geological: physical barriers
Isolation and Speciation
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Drawing the process
Isolation and Speciation
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Zygote:
Fertilization
Sperm (Male)
First cell
of an
organism
Ovum (Female)
Zygote (Fertilized Ovum)
Gametes: sex cells
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2 Types of Isolation:
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Prezygotic Isolation: occur BEFORE fertilization
Postzygotic Isolation: occur AFTER fertilization
Isolation and Speciation
Spatial
Geographical
Gametic
Mechanical
Behavioral
Prezygotic
Isolation
Mechanisms:
Habitat
Temporal
Isolation and Speciation
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Prezygotic Isolation Mechanisms: Spatial
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Large separation, individuals never meet so no breeding occurs
Example: Lizards in Northern California and in Southern California
Isolation and Speciation
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Prezygotic Isolation Mechanisms: Geographical
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Separation be geographical barrier: rivers, mountains, etc.
Isolation and Speciation
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Prezygotic Isolation Mechanism: Habitat Isolation
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SAME AREA, different habitats = no chance to mate
Example: snake in water and snake on land
Isolation and Speciation
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Prezygotic Isolation Mechanisms: Temporal
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SAME AREA, populations mate at different times of the year
Example: Western Spotted Skunk mates in summer, Eastern
Spotted Skunk mates in winter.
Isolation and Speciation
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Prezygotic Isolation Mechanisms: Behavioral
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SAME AREA, populations have unique courtship dances and
songs that prevent them from mating with other populations
Example: Western Meadowlark (flute-like song) and Eastern
Meadowlark (whistled song)
Isolation and Speciation
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Prezygotic Isolation Mechanisms: Mechanical Isolation
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SAME AREA, genitalia does not fit together, so mating cannot
occur
Example: black sage and white sage can’t fertilize each other
b/c they are structurally different and pollinated by dif. insects.
Isolation and Speciation
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Prezygotic Isolation Mechanisms: Gametic Isolation
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Egg and sperm from two organisms are incompatible (generally
for aquatic animals)
Example: sea urchin release eggs and sperm into water.
Fertilization only occurs if the eggs and sperm match up with
each other, so the three species of sea urchin do not
interbreed.
Isolation and Speciation
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Hybrid: offspring of two different species
Hybrid
Inviability
Postzygotic
Isolation
Mechanisms
Hybrid
Breakdown
Hybrid
Sterility
Isolation and Speciation
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Postzygotic Isolation Mechanism: Hybrid Inviability
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Hybrid offspring dies before reaching reproductive age
(includes death after birth and miscarriage during pregnancy)
Example: Hybrid of goat and sheep dies before birth
Isolation and Speciation
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Postzygotic Isolation Mechanisms: Hybrid Sterility
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Hybrid is sterile/infertile (unable to have offspring), NOT A
SPECIES. Recall: species are able to mate together!
Example: Horse + Donkey = Mule (sterile)
Isolation and Speciation
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Postzygotic Isolation Mechanism: Hybrid Breakdown
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Sterility arises after a few generations. Parents have a hybrid.
Hybrid has its own offspring. Those offspring are sterile.
Example: Two cottons (Gossypium hirsutum and Gossypium
barbadense) have fertile hybrid offspring. Those hybrids can
have their own offspring. But this generation is sterile.
Reading/Work Time
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Cornell Notes on Section 15.2 Pg 409-413
Questions:
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15.2 #2-5
Chapter 15 Assessment #3, 4, 8, 11, 15, 21-34