Week 5!!

Get ready for entrance quizLabs—Discussions and graphs

need work

Evolution evidence: Biogeography

• Geographical distribution of species

• Examples:Islands vs.

Mainland AustraliaContinents

Evolution evidence: The Fossil Record

• Succession of forms over time

• Transitional links• Vertebrate descent

Fossil Record

2006 Fossil Discovery of Early Tetrapod• Tiktaalik

– “missing link” from sea to land animals

Evolution evidence: Comparative Anatomy

• Homologous structures (homology)

• Descent from a common ancestor

Homologous structures• Similar structure

• Similar development

• Different functions

• Evidence of close evolutionary relationship– recent common ancestor

spines

tendrils

succulent leaves

colored leaves

Homologous structures

leaves

needles

Analogous structures Separate evolution of structures

similar functions similar external form different internal structure & development different origin no evolutionary relationship

Solving a similar problem with a similar solutionSolving a similar problem with a similar solution

Don’t be fooledby their looks!

Vestigial organs• Modern animals may have structures that serve

little or no function– remnants of structures that were functional in

ancestral species– deleterious mutations accumulate in genes for non-

critical structures without reducing fitness• snakes & whales — remains of pelvis & leg bones of

walking ancestors• eyes on blind cave fish• human tail bone

Dispatch

1) Compare analogous to homologous structures

2) What are 3 pieces of evidence that whales evolved from land mammals?

3) Give 2 examples of vestigial structures.

Evolution evidence: Comparative Embryology

• Pharyngeal pouches, ‘tails’ as embryos

Evolution evidence: Molecular Biology

• Similarities in DNA, proteins, genes, and gene products

• Common genetic code

Closely related species have sequences that are more similar than distantly related species DNA & proteins are a molecular

record of evolutionary relationships

Building “family” trees

Closely related species (branches) share same line of descent until their divergence from a common ancestor

Artificial selection

• Artificial breeding can use variations in populations to create vastly different “breeds” & “varieties”

“descendants” of the wolf

“descendants” of wild mustard

Natural selection in action

• Insecticide & drug resistance– insecticide didn’t

kill all individuals

– resistant survivors reproduce

– resistance is inherited

– insecticide becomes less & less effective

Final words…...

• “Absence of evidence is not evidence of absence.”

Evolution on a micro level

• Looking at alleles

• Looking at the DNA

• DARWIN DIDN”T KNOW DNA

Get a bottle and colored sticks

Microevolution, II: type of genetic drift

• The Bottleneck Effect: type of genetic drift resulting from a reduction in population (natural disaster) such that the surviving population is no longer genetically representative of the original population

Microevolution, I

• A change in the gene pool of a population over a succession of generations

• 1- Genetic drift: changes in the gene pool of a small population due to chance (usually reduces genetic variability)

Chapter 23~

• Chapter 23~ The Evolution of Populations

Population genetics• Population:

a localized group of individuals belonging to the same species

• Species: a group of populations whose

individuals have the potential to interbreed and produce fertile offspring

• Gene pool: the total aggregate of genes in

a population at any one time

• Population genetics: the study of genetic changes in

populations

• Modern synthesis/neo-Darwinism

• “Individuals are selected, but populations evolve.”

Conservation issues• Bottlenecking is an important

concept in conservation biology of endangered species– loss of alleles from gene pool– reduces variation– reduces adaptability

Breeding programs must consciously outcrossBreeding programs must consciously outcross

Peregrine Falcon

Golden Lion Tamarin

Microevolution, III type of genetic drift• Founder Effect:

a cause of genetic drift attributable to colonization by a limited number of individuals from a parent population– just by chance some rare

alleles may be at high frequency; others may be missing

– skew the gene pool of new population

• human populations that started from small group

of colonists• example:

colonization of New World

Dispatch

1) Compare and contrast:

-founder effect

-genetic drift

-bottle neck effect

2) Give 3 deadlines for October

Microevolution, IV• 2- Gene Flow:

genetic exchange due to the migration of fertile individuals or gametes between populations (reduces differences between populations)

• seed & pollen distribution by wind & insect

• migration of animals

Microevolution, V

• 3- Mutations: a change in an organism’s DNA (gametes; many generations); original source of genetic variation (raw material for natural selection)

• Mutation creates variation

Microevolution, VI

• 4- Nonrandom mating:

• Sexual selection• inbreeding and

assortive mating (both shift frequencies of different genotypes)

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Sexual selection

It’s FEMALE CHOICE, baby!

Microevolution, VII5.NaturalSelection• differential success

in reproduction; • climate change

• food source availability

• predators, parasites, diseases

• toxins

• only form of microevolution that adapts a population to its environment

• combinations of alleles that provide “fitness” increase in the population

Natural Selection

• Selection acts on any trait that affects survival or reproduction– predation selection– physiological selection– sexual selection

Variation & natural selection • Variation is the raw material for natural

selection– there have to be differences within population

– some individuals must be more fit than others

Mean beak depth of parents (mm)

Medium ground finch8

8 9 10 11

9

10

11

1977 1980 1982 1984

Dry yearDry year

Dry year

Wet year

Bea

k de

pth

Bea

k de

pth

ofof

fspr

ing

(mm

)

Where does Variation come from?• Mutation

– random changes to DNA• errors in mitosis & meiosis• environmental damage

• Sex – mixing of alleles

• recombination of alleles– new arrangements in every offspring

• new combinations = new phenotypes

– spreads variation• offspring inherit traits from parent

Population variation

• Polymorphism: coexistence of 2 or more distinct forms of individuals (morphs) within the same population

• Geographical variation: differences in genetic structure between populations (cline)

Variation preservation

• Prevention of natural selection’s reduction of variation

• Diploidy 2nd set of chromosomes hides variation in the heterozygote

• Balanced polymorphism 1- heterozygote advantage (hybrid vigor; i.e., malaria/sickle-cell anemia); 2- frequency dependent selection (survival & reproduction of any 1 morph declines if it becomes too common; i.e., parasite/host)

Natural selection

• Fitness: contribution an individual makes to the gene pool of the next generation

• 3 types:• A. Directional• B. Diversifying• C. Stabilizing

Effects of Selection• Changes in the average trait of a population

DIRECTIONALSELECTION

STABILIZINGSELECTION

DISRUPTIVESELECTION

giraffe neckhorse size human birth weight rock pocket mice

Sexual selection

• Sexual dimorphism: secondary sex characteristic distinction

• Sexual selection: selection towards secondary sex characteristics that leads to sexual dimorphism

Any Questions??

Hardy-Weinberg Theorem• Serves as a model for the genetic

structure of a nonevolving population (equilibrium)

• Evolution = change in allele frequencies in a population

– hypothetical: what conditions not would cause allele frequencies to change?

– non-evolving population

REMOVE all agents of evolutionary change

1. very large population size (no genetic drift)

2. no migration (no gene flow in or out)

3. no mutation (no genetic change)

4. random mating (no sexual selection)

5. no natural selection (everyone is equally fit)

Hardy-Weinberg Equation• p=frequency of one allele (A); q=frequency of the other

allele (a); p+q=1.0 (p=1-q & q=1-p)

• p2=frequency of AA genotype; 2pq=frequency of Aa genotype; q2=frequency of aa genotype;

• frequencies of all individuals must add to 1 (100%), so:

p2 + 2pq + q2 = 1

G.H. Hardymathematician W. Weinberg

physician

What are the genotype frequencies?What are the genotype frequencies?

Using Hardy-Weinberg equation

q2 (bb): 16/100 = .16

q (b): √.16 = 0.40.4

p (B): 1 - 0.4 = 0.60.6

q2 (bb): 16/100 = .16

q (b): √.16 = 0.40.4

p (B): 1 - 0.4 = 0.60.6

population: 100 cats84 black, 16 whiteHow many of each genotype?

population: 100 cats84 black, 16 whiteHow many of each genotype?

bbBbBB

p2=.36p2=.36 2pq=.482pq=.48 q2=.16q2=.16

Must assume population is in H-W equilibrium!Must assume population is in H-W equilibrium!

Hardy Problem

• Calculate q2 Count the individuals that are homozygous recessive in the illustration above. Calculate the percent of the total population they represent. This is q2.

Calculate q

Q2=4/16=0.25

Q=0.5

p + q = l. You know q, so what is p, the frequency of the dominant allele?

P=0.5

Find 2pq 2pq = 2(0.5) (0.5) = 0.5 , so 50% of the population is heterozygous.

Problem 1

• In a certain population of 1000 fruit flies, 640 have red eyes while the remainder have sepia eyes. The sepia eye trait is recessive to red eyes. How many individuals would you expect to be homozygous for red eye color? Hint: The first step is always to calculate q2! Start by determining the number of fruit flies that are homozygous recessive. If you need help doing the calculation, look back at the Hardy-Weinberg equation.

Problem 2

• The Hardy-Weinberg equation is useful for predicting the percent of a human population that may be heterozygous carriers of recessive alleles for certain genetic diseases. Phenylketonuria (PKU) is a human metabolic disorder that results in mental retardation if it is untreated in infancy. In the United States, one out of approximately 10,000 babies is born with the disorder. Approximately what percent of the population are heterozygous carriers of the recessive PKU allele?