Question of the Day Mar 14Question of the Day Mar 14

• Which is not true about a species?

• A. Members live in populations

• B. They cannot breed with one another

• C. They can breed between different populations.

• D. All members contribute to the species gene pool.

AGENDA Mar 14AGENDA Mar 14

• Objective: Investigate how genetic variation is responsible for natural selection.

• 1. Question of the DAY

• 2. Chapter 16-1 Genes and Variation3. Homework Check 16-1 Guided Reading

• 4. Review and Homework– 16-2 Guided Reading

Chapter 16Chapter 16

Evolution of Evolution of

PopulationsPopulations

16-1: Genes and Variation16-1: Genes and Variation• natural selection relies on

variation

• genes are the source of inheritable variation

• when variation occurs, nature selects the successful ones

• individuals do not change, a population does

Genes and VariationGenes and Variation

• At least two different alleles account for inherited traits.– Body size, coat color, seed shape

• “Invisible” variation also present– Small differences in biochemical processes

Genes and VariationGenes and Variation

• Individual organisms are heterozygous for many genes

15% of genes in insects

4 – 8% in fish, reptiles, and mammals

Evolution as Genetic ChangeEvolution as Genetic Change• evolutionary biologists study

populations – collection of individuals of the

same species in a given area– share a gene pool

• relative frequency: number of times an allele occurs in a gene pool compared with the number of times other alleles for the same gene occur

• What is the relative frequency of the purple allele?

Genetic Variation within a SpeciesGenetic Variation within a Species

• species: group of similar organisms that breed with each other and produce viable offspring because they share the same gene pool

• How do mutations occur?– Mistakes in replication, radiation, and

chemicals

• Gene Shuffling - Meiosis

Genetic Variation within a SpeciesGenetic Variation within a Species• How many different combinations of genes

can be produced from homologous x-somes in a human?– 8.4 million

• Number of phenotypes produced for a trait depends on how many genes control the trait– Single-gene trait

– Polygenic trait

Single-gene and PolygenicSingle-gene and Polygenic

QUESTION of the DAY Mar 17QUESTION of the DAY Mar 17

• The success of an organism in surviving and reproducing is a measure of

• A. an adaptation to an environmental factor

• B. its fitness

• C. its polygenic traits

• D. single gene traits

AGENDA Mar 17AGENDA Mar 17

• Objective: Explain the five conditions needed to maintain genetic equilibrium.

• 1. Question of the DAY• 2. Chapter 15 Test Grades in GENESIS• 3. Chapter 16-2 Evolution as Genetic Change

4. Homework Check 16-2 Guided Reading• 5. Review and Homework

16-2 Evolution as Genetic Change16-2 Evolution as Genetic Change• Why does natural selection never act on specific

genes?• An entire organism either survives and reproduces

or dies out.

• Organisms that die do not contribute to gene pool.

• Relative frequencies within a population change over time.

Natural Selection on Single Gene TraitsNatural Selection on Single Gene Traits

• Leads to changes in allele frequencies

• Consider a population of lizards…

• Normal skin = Brown

• Mutations produce Red and Black skin

• Predict the number of red lizards after 30 generations if the environment the lizards live in is a desert.

• Black lizards? WHY?

Natural Selection on Polygenic TraitsNatural Selection on Polygenic Traits

• What type of curve is produced when measuring a range of phenotypes?

• Bell curve

• Interpret the phenotypes found within the individuals of this population.

Three types of SelectionThree types of Selection

• Directional Selection – individuals at one end of the curve have higher fitness than those in middle or at the end.

• Dotted line = Original distribution of individuals

Types of SelectionTypes of Selection

• Stabilizing Selection – Individuals near the center of the curve have higher fitness than any other individuals.

• Dotted line = Original

distribution of human

babies

Types of SelectionTypes of Selection

• Disruptive Selection – Individuals at upper and lower ends of curve have higher fitness than those in the middle.

• Dotted line = Original

distribution of

individuals

Types of AdaptationsTypes of Adaptations• Morphological Adaptation: Structural feature that aids a

species in fitting into its environment.

• Physiological Adaptation: An adjustment of the body involving metabolic processes that allows an organism to best adapt to its environment.

• Behavioral Adaptation: Traits that develop to better allow an organism to survive or reproduce.– Bears hibernating in winter– Sheep running away from types of noises

ExamplesExamples

QUESTION of the DAY Mar 18QUESTION of the DAY Mar 18• When average sized seeds become more scarce

but smaller and larger seeds are still available as food sources, the type of selection that represents this change is

• A. Directional• B. Disruptive• C. Stabilizing• D. Drifting

AGENDA Mar 18AGENDA Mar 18

• Objective: Apply Hardy-Weinberg equations to determine allele frequencies.

• 1. Question of the DAY• 2. Chapter 16-2 Hardy-Weinberg Equilibrium

– Problem Solving

• 3. Review and Homework

GENETIC DRIFTGENETIC DRIFT• What controls genetics and the passing down of genes?• PROBABILITY

• Genetic drift: random change in the frequency of a gene that happens by chance– Greater # of changes as population sizes decrease

• Founder effect – change in allele frequencies due to the migration of a small subgroup of individuals.

Hardy-Weinberg PrincipleHardy-Weinberg Principle• states that allele frequencies in a population will remain

constant unless one or more factors cause those frequencies to change

• only applies during genetic equilibrium: when allele frequencies remain constant

• Conditions to maintain equilibrium• random mating • very large population• no movement into or out of the population• no mutations• no natural selection

Calculating Gene FrequenciesCalculating Gene Frequencies• when a population is in Hardy-Weinberg equilibrium,

genotypes can be calculated from allele frequencies

• p + q = 1 p2 + 2pq + q2 = 1

• p = dominant allele• q = recessive allele • p2 = homozygous dominant • 2pq = heterozygous• q2 = homozygous recessive

Hardy-Weinberg ProblemsHardy-Weinberg Problems• In a population of 3000 fruit flies, 270 flies have

white eyes. White eye color is the recessive trait. Determine the frequencies of the red and white eye color alleles. How many flies are heterozygous for red eye color?

• APPLY the 2 H-W Equations.

SOLUTIONSOLUTION• STEP 1 – Determine q2

• STEP 2 – Find q and p

• STEP 3 – Determine p2

• STEP 4 – Find 2pq

• STEP 5 – Find # of heterozygous flies

Hardy-Weinberg ProblemHardy-Weinberg Problem• Coloration in the scarlet tiger moth is listed

below for 1612 individuals.• White-spotted (AA) = 1469 • Intermediate (Aa) = 138 • Little spotting (aa) =5

• Calculate the following frequencies.• A, a, AA, Aa, and aa

16-3: The Development of New Species16-3: The Development of New Species• speciation: process in which new

species evolve from old ones• niche: combination of an

organism’s profession and the place it lives

• no two species can occupy the same niche in the same location for a long period of time

• any species that occupies an unoccupied niche will better survive and potentially form a new species

Process of SpeciationProcess of Speciation• new species form when

populations are separated

• reproductive isolation: when populations are separated so they do not interbreed

• when populations better adapt to different environments, their gene pools become dissimilar

• Darwin’s finches

Mechanisms of Reproductive IsolationMechanisms of Reproductive Isolation

• Behavioral isolation – two populations– Capable of interbreeding– Differences in courtship rituals or reproductive

strategies– Eastern and western meadowlarks

• Different mating songs

– http://www.bing.com/videos/search?q=animal+courtship+displays&FORM=HDRSC3#view=detail&mid=B99AA83542EC45E6463EB99AA83542EC45E6463E

MechanismsMechanisms

• Geographic isolation – two population separated by geographic barriers– Mountains, rivers, bodies of water

– Does not guarantee isolation.

– May not isolate every organism from one another

MechanismsMechanisms

• Temporal isolation – two or more species reproduce at different times.

• Similar orchids living in a rain forest.– Each releases pollen at a different time

Peter and Rosemary GrantPeter and Rosemary Grant

• Tested natural selection• Documented effects in finches on Galapagos

• Individual birds with different beak sizes had different chances of survival during a drought

• Big-beaked birds – obtain food when scarce– mate with other big-beaked birds

Speciation in Darwin’s FinchesSpeciation in Darwin’s Finches

• 1. Founders species – first finches arrive on Galapagos

• 2. Geographic isolation - Some finches arrived on another island and adapted to survive

• 3. Different Gene Pools on each island

• 4. Reproduction isolation – Two species on same island– finches mate with those having same beak size

• 5. Competition – both species compete on same island

• 6. Continued evolution – produced 13 different species

Speciation and Adaptive RadiationSpeciation and Adaptive Radiation

• adaptive radiation: process in which one species gives rise to many species– also known as divergent evolution

• convergent evolution: process in which different species evolve to have similar appearances and behaviors

• analogous structures: structures that are similar in appearance and function but have different origins

Pace of EvolutionPace of Evolution• punctuated

equilibrium: involves long periods of stability that are interrupted by episodes of rapid change

• gradualism: evolution occurs slow and steady over a long period of time