Chapter 17.2 Genetic Change Chapter 17.2 Genetic Change

17.3 Speciation17.3 Speciation

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DefinitionsDefinitionsGene poolGene pool: All alleles of the population’s : All alleles of the population’s

genes.genes.

Allelic frequencyAllelic frequency: % of a specific allele in : % of a specific allele in the gene pool. Example: See Figure 5 Page the gene pool. Example: See Figure 5 Page 404 Snapdragon Flower404 Snapdragon Flower

Genetic EquilibriumGenetic Equilibrium: This exists when the : This exists when the frequency of alleles remains the same over frequency of alleles remains the same over generations. The population is not evolving.generations. The population is not evolving.

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5 Different “Forces” That 5 Different “Forces” That Can Cause EvolutionCan Cause Evolution

1. Gene Flow1. Gene Flow 2. Non-random Mating (Sexual Selection)2. Non-random Mating (Sexual Selection) 3. Mutation3. Mutation 4. Genetic Drift4. Genetic Drift 5. Natural Selection5. Natural Selection

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Gene FlowGene Flow Gene Flow occurs when genes are added or Gene Flow occurs when genes are added or

removed from a populationremoved from a population Example: Migration Example: Migration

These caribou are migrating from one place to These caribou are migrating from one place to another. If they meet other groups of caribou and another. If they meet other groups of caribou and interbreed, gene flow may occur. interbreed, gene flow may occur.

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Non-random Mating Non-random Mating (Sexual Selection)(Sexual Selection)

Females sometimes select mates based on the Females sometimes select mates based on the male’s size, color, ability to gather food, or other male’s size, color, ability to gather food, or other characteristics. characteristics.

Example: The vibrant red stripe of the blue muzzle of Example: The vibrant red stripe of the blue muzzle of this male (right) mandrill baboon does not appear in this male (right) mandrill baboon does not appear in females (left).females (left).

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Non-random Mating Non-random Mating (Sexual Selection)(Sexual Selection)

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MutationMutation When the DNA code of organisms When the DNA code of organisms

changes randomly (Creates new alleles)changes randomly (Creates new alleles)

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Genetic DriftGenetic Drift Chance events, such as fires, floods or storms, can Chance events, such as fires, floods or storms, can

cause rare alleles to be lost. cause rare alleles to be lost. This occurs more often in populations that are This occurs more often in populations that are

small in sizesmall in size.. Genotypes Genotypes can change as a result.can change as a result.

ExampleExample: A wildflower population ... consisted : A wildflower population ... consisted of only 25 plants. Assume that 16 of the plants of only 25 plants. Assume that 16 of the plants have the genotype AA for flower color, 8 are Aa, and only 1 is aa. have the genotype AA for flower color, 8 are Aa, and only 1 is aa.

Now imagine that three of the plants are accidently destroyed by Now imagine that three of the plants are accidently destroyed by a rock slide before they have a chance to reproduce. By chance, a rock slide before they have a chance to reproduce. By chance, all three plants lost from the population could be AA individuals. all three plants lost from the population could be AA individuals.

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Natural SelectionNatural Selection Can remove Can remove

individuals with certain individuals with certain traits from a traits from a population. population.

The alleles for those The alleles for those traits may become traits may become less common in the less common in the population over timepopulation over time..

Example: Horse Evolution Example: Horse Evolution

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Evolutionary FitnessEvolutionary Fitness

How How long an individual can survive long an individual can survive and how many and how many offspring they can offspring they can produceproduce to pass genes to future to pass genes to future generations??? generations???

This is their “Evolutionary This is their “Evolutionary Fitness”.Fitness”.

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Who has the Higher Who has the Higher EEvolutionary Fitnessvolutionary Fitness??

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3 Types of Natural Selection3 Types of Natural Selection

Directional SelectionDirectional Selection – favors one of the – favors one of the extreme variations of a traitextreme variations of a trait

Stabilizing SelectionStabilizing Selection – favors average – favors average individualsindividuals

Disruptive SelectionDisruptive Selection – favors individuals with – favors individuals with both extremes of a trait (eliminates intermediate both extremes of a trait (eliminates intermediate phenotypes)phenotypes)

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17.3 Biological Species 17.3 Biological Species ConceptConcept

When Males and Females of the same When Males and Females of the same species reproduce and their offspring are species reproduce and their offspring are fertile and can pass on their genes they fertile and can pass on their genes they are considered a species.are considered a species.

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Sterile HybridsSterile Hybrids

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Liger Mule

SpeciationSpeciation Speciation occurs when members of Speciation occurs when members of

similar populations similar populations no longer interbreed no longer interbreed to produce fertile offspring to produce fertile offspring within their within their natural environment.natural environment.

Example: Squirrels that live in the Grand Example: Squirrels that live in the Grand CanyonCanyon

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Species definition does Species definition does not always applynot always apply

Some organisms reproduce Asexually:Some organisms reproduce Asexually: Bacteria and ArchaebacteriaBacteria and Archaebacteria

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Types of Speciation Types of Speciation a. Geographic Barrier- A physical barrier a. Geographic Barrier- A physical barrier

that prevents interbreeding (Mountain, that prevents interbreeding (Mountain, River, Island)River, Island)

b. Change in Mating Behavior and Timingb. Change in Mating Behavior and Timing

c. Change in Niche (Food source)c. Change in Niche (Food source)

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a. Geographic Isolationa. Geographic Isolation

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Geographic IsolationGeographic Isolation

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Examples of how this can happen:

1.A pond dries up somewhat to make two ponds, 2.A river becomes re-routed so that it cuts through a field, 3.Two land masses drift apart over time, 4.A few seeds stuck on a bird's feather fall by chance on a new island 5.A new road goes up between 2 fields, 6.A flood washes a small population of lizards to an island....etc

Geographic IsolationGeographic Isolation

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Change in Change in b. Mating Behavior and b. Mating Behavior and

TimingTiming Many species that sexually reproduce have Many species that sexually reproduce have

specific behaviors for attracting mates, such specific behaviors for attracting mates, such as a pattern of sounds or actions.as a pattern of sounds or actions.

Example: The pickerel frog and the leopard Example: The pickerel frog and the leopard frog are closely related species. frog are closely related species. Differences in mating times may have Differences in mating times may have caused their reproductive isolation. caused their reproductive isolation.

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TimingTiming Similar species have different breeding Similar species have different breeding

seasons seasons Eastern SpottedEastern Spotted Western Spotted Western Spotted

SkunkSkunk Skunk Skunk

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Bizarre Mating RitualsBizarre Mating Rituals The male anglerfish latches onto the female The male anglerfish latches onto the female

like a parasite, living off her food and fertilizing like a parasite, living off her food and fertilizing her when she's ready to lay eggs. her when she's ready to lay eggs.

The male octopus's penis breaks off during The male octopus's penis breaks off during mating, but don't worry, it will grow back the mating, but don't worry, it will grow back the following season. following season.

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Bizarre Mating RitualsBizarre Mating Rituals Emperor Penguins travel as far as 70 miles on Emperor Penguins travel as far as 70 miles on

foot to reach the breeding site. They look for foot to reach the breeding site. They look for their mates by making a bugling call. Once their mates by making a bugling call. Once they find one another, they stand breast to they find one another, they stand breast to breast, repeatedly bow to each other and sing. breast, repeatedly bow to each other and sing.

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c. Change in Nichec. Change in Niche Divergence can happen when populations Divergence can happen when populations

use different nichesuse different niches

Example: The members of a particular Example: The members of a particular population of insects live and feed high up in population of insects live and feed high up in the trunks of trees. As time passes, some the trunks of trees. As time passes, some members of the population begin to feed on members of the population begin to feed on different parts of the trees. Eventually the 2 different parts of the trees. Eventually the 2 groups diverge and no longer interbreed. groups diverge and no longer interbreed.

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Artificial SpeciationArtificial Speciation

Diane Dodd’s fruit fly lab, 19892828

What is Extinction?What is Extinction? When a species fails to produce any offspringWhen a species fails to produce any offspring 99%99% of all species that have ever lived on of all species that have ever lived on

Earth are now extinctEarth are now extinct

2929Dodo Bird

Tasmanian Tiger

Wooly Mammoth

T Rex

The EndThe End

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