Semester 2, Day 12

Fossil Evidence of Evolution

Homework Due Cornell Notes on 14.3 and 14.4 Questions:

14.3 #1-3 14.4 #1-5 Chapter 14 Assessment #3, 4, 6, 10-14, 16, 20,

22a, 22c

Isolation and Speciation Speciation: process of creating a new species

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.

Isolation: a way in which to prevent species from breeding Over time, isolation results in speciation

Barrier: anything that separates species from each other Reproductive: prevents them from breeding Geological: physical barriers

Isolation and Speciation Drawing the process

Isolation and Speciation Zygote:

2 Types of Isolation: Prezygotic Isolation: occur BEFORE fertilization Postzygotic Isolation: occur AFTER fertilization

Fertilization

Sperm (Male) Ovum (Female)

Zygote (Fertilized Ovum)

First cell of

an organis

m

Gametes: sex cells

Isolation and Speciation

Prezygotic Isolation

Mechanisms:

Spatial

Geographical

Habitat

TemporalBehavioral

Mechanical

Gametic

Isolation and Speciation Prezygotic Isolation Mechanisms: Spatial

Large separation, individuals never meet so no breeding occurs

Example: Lizards in Northern California and in Southern California

Isolation and Speciation Prezygotic Isolation Mechanisms:

Geographical Separation be geographical barrier: rivers,

mountains, etc.

Isolation and Speciation Prezygotic Isolation Mechanism: Habitat

Isolation SAME AREA, different habitats = no chance to

mate Example: snake in water and snake on land

Isolation and Speciation Prezygotic Isolation Mechanisms: Temporal

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 Prezygotic Isolation Mechanisms: Behavioral

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 Prezygotic Isolation Mechanisms: Mechanical

Isolation 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 Prezygotic Isolation Mechanisms: Gametic

Isolation 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 Hybrid: offspring of two different species

Postzygotic Isolation

Mechanisms

Hybrid Inviability

Hybrid Sterility

Hybrid Breakdown

Isolation and Speciation Postzygotic Isolation Mechanism: Hybrid

Inviability 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 Postzygotic Isolation Mechanisms: Hybrid

Sterility 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 Postzygotic Isolation Mechanism: Hybrid

Breakdown 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 Cornell Notes on Section 15.2 Pg 409-413 Questions:

15.2 #2-5 Chapter 15 Assessment #3, 4, 8, 11, 15, 21-34