Microevolution

2012-2013

Selective Breeding & Evolution

• Evolution is genetic change in a line of descent through successive generations

• Selective breeding practices yield evidence that heritable changes do occur

Chickens

Domestication of Dogs

• Began about 50,000 years ago

• 14,000 years ago - artificial selection– Dogs with desired forms of traits

were bred

• Modern breeds are the result

Dog Breeds

Silver Fox Video

• Segment from a BBC Documentary

• http://www.youtube.com/watch?v=ot2www2CF3Y

• Cornell Website: Study of the Molecular Basis of Tame and Aggressive Behavior in the Silver Fox Model

• http://cbsu.tc.cornell.edu/ccgr/behaviour/Index.htm

Silver Fox Fur Trade

The Case of the Silver Fox

“To investigate the domestication process as an evolutionary phenomenon, academician D.K. Belyaev began a wide-scale experiment on domestication of different animals. A population of silver-black foxes that may be considered genetically adapted to humans and man-made factors on all parameters was bread as a result of multi-year selection. It is extremely important that such behavior develops on the genetic base and is preserved stable both in ontogenesis and in further generations. The population is unique as it has no analogues worldwide”. http://tinyurl.com/4mojzp4

http://www.hum.utah.edu/~bbenham/2510%20Spring%2009/Behavior%20Genetics/Farm-Fox%20Experiment.pdf (Please read this article).

Results of Artificial Selection

• Extremes in size– Great Dane and Chihuahua

• Extremes in form– Short-legged dachshunds

– English bulldog

• Short snout and compressed face

• Extreme traits lead to health problems

Evolutionary Theories

• Widely used to interpret the past and present, and even to predict the future

• Reveal connections between the geological record, fossil record, and organism diversity

Early Scientific Theories

• Hippocrates - All aspects of nature can be traced to their underlying causes

• Aristotle - Each organism is distinct from all the rest and nature is a continuum or organization

Great Chain of Being

?

Confounding Evidence( to the Great Chain of Being Concept)

• Biogeography

• Comparative anatomy

• Geologic discoveries

Biogeography

• Size of the known world expanded

enormously in the 15th century

• Discovery of new organisms in previously

unknown places could not be explained

by accepted beliefs

– How did species get from center of creation

to all these places?

What, How, and Where?

Biogeography

• Biogeography is the study of the geographical patterns of plant and animal species.

BioRealms

Comparative Morphology

• Study of similarities and differences in body plans of major groups

• Puzzling patterns:– Animals as different as whales and bats have

similar bones in forelimbs

– Some parts seem to have no function

– (vestigial)

Vertebrate Forelimbs

Bat Human Whale

Wolf Paw Anatomy

Vestigial Anatomy

Geological Discoveries

• Similar rock layers throughout world

• Certain layers contain fossils

• Deeper layers contain simpler fossils

than shallow layers

• Some fossils seem to be related to

known species

Dinosaur Fossils Etc

Acrocanthosaurus Skull

Size 56" long.Weight 150 lb'sCost $9,500 with stand.

Grand Canyon

19th Century - New Theories

• Scientists attempt to reconcile evidence of change with traditional belief in a single creation event

• Two examples– Georges Cuvier - multiple catastrophes– Jean Lamarck - inheritance of acquired

characteristics

The Theory of Uniformity

• Lyell’s Principles of Geology

• Subtle, repetitive processes of change had shaped Earth

• Challenged the view that Earth was only 6,000 years old

Erosion

Wind and water produce hoodoos.

In German

Darwin’s Voyage

• At age 22, Charles Darwin began a five-year, round-the-world voyage aboard the Beagle

• In his role as ship’s naturalist, he collected and examined the species that inhabited the regions the ship visited

Voyage of the Beagle

EQUATOR

GalapagosIslands

GalapagosIslands

Isabela

Darwin

Wolf

Pinta

Marchena Genovesa

Fernandia

SantiagoBartolomé

RabidaPinzon

SeymourBaltra

Santa Cruz

Santa Fe

Tortuga

Española

San Cristobal

Floreana

Volcanic islands far off coast of Ecuador

All inhabitants are descended from species that arrived on islands from elsewhere

Malthus - Struggle to Survive

• Thomas Malthus, a clergyman and economist, wrote essay that Darwin read on his return to England

• Argued that as population size increases, resources dwindle, the struggle to live intensifies, and conflict increases

Malthusian CatastropheStopped Here

Galapagos Finches

• Darwin observed finches with a variety of lifestyles and body forms

• On his return, he learned that there were 13 species

• He attempted to correlate variations in their traits with environmental challenges

Beaks

Galapagos Finches

Galapagos Tortoises

Darwin’s Theory

A population can change over time when

individuals differ in one or more heritable

traits that are responsible for differences

in the ability to survive and reproduce.

Darwin's Explanatory Model of Evolution Through Natural

Selection*

• Note: An understanding of evolution by natural selection is accessible to all.

• *Source: BSCS Green Version of Biology

Facts 1, 2, and 3

• 1. Potential exponential increase in populations (superfecundity) (Source: Paley, Malthus, and others)

• 2. Observed steady-state of stability of populations (Source: universal observations)

• 3. Limitations of resources (Source: observation reinforced by Malthus)

Superfucundity

Far more offspring are produced than survive to adulthood.

Termites……..

Inference 1

• Struggle for existence among individuals (Author of inference: Malthus)

Facts 4 and 5

• Fact 4

• Uniqueness of the individual (Source: animal breeders, taxonomists)

• Fact 5

• Heritability of much of the individual variation (Source: animal breeders)

Genetic Basis for the Inheritance of Phenotypes

Genetics provides a firm foundation.

Inference 2

• Differential survival and reproduction i.e. natural selection (Author of inference: Darwin)

Inference 3

• Through many generations: evolution. (Author of inference: Darwin)

The theory of evolution by natural selection is composed of facts and inferences. Biologists have universally found this theory to be the best account for the fossil record, biodiversity, comparative anatomy, biogeography, drug resistance in bacteria, etc.

Like all scientific theories it represents the best that science has to offer, but still it must be tested with any new scientific information and may be modified accordingly.

So far the theory of evolution by natural selection is the best scientific model for the biotic world.

“Sister Species”

Aphelocoma insularis Aphelocoma californica

Florida Scrub Jay Western Scrub Jay

Distributions

Alfred Wallace(STOPPED HERE)

• Naturalist who arrived at the same

conclusions Darwin did

• Wrote to Darwin describing his views

• Prompted Darwin to finally present his

ideas in a formal paper

Alfred Russel Wallace

• The Wallace Effect is the hypothesis that natural selection can contribute to the reproductive isolation of incipient species by encouraging varieties to develop barriers to hybridization.

• He is best known for

independently proposing a theory of natural selection.

Populations Evolve

• Biological evolution does not change individuals

• It changes a population

• Traits in a population vary among individuals

• Evolution is change in frequency of traits

Variation in Color Pattern

The Gene Pool

• All of the genes in the population

• Genetic resource that is shared (in theory) by all members of population

Variation in Phenotype

• Each kind of gene in gene pool may have two or more alleles

• Individuals inherit different allele combinations

• This leads to variation in phenotype

• Offspring inherit genes, not phenotypes

What Determines Alleles in New Individual?

• Mutation • Crossing over at meiosis I• Independent assortment

• Fertilization

• Change in chromosome number or

structure

Crossing Over

Genetic Equilibrium

• Allele frequencies at a locus

are not changing

• Population is not evolving

Five Conditions

• No mutation

• Random mating

• Gene doesn’t affect survival or

reproduction

• Large population

• No immigration/emigration

Microevolutionary Processes

• Drive a population away from genetic equilibrium

• Small-scale changes in allele frequencies brought about by:– Natural selection

– Gene flow

– Genetic drift

– Sexual Selection

Gene Mutations

• Infrequent but inevitable

• Each gene has own mutation rate

• Lethal mutations

• Neutral mutations

• Advantageous mutations

Hardy-Weinberg Rule

At genetic equilibrium, proportions of genotypes at a locus with two alleles are given by the equation:

p2 AA + 2pq Aa + q2 aa = 1

Frequency of allele A = p

Frequency of allele a = q

p + q = 1

Punnett Square

AA(p2) Aa(pq)

Aa(pq) aa(q2)

Ap aq

Ap

aq

Frequencies in Gametes

A A A a a a

0.49 AA 0.42 Aa 0.09 aa

0.49 + 0.21 0.21 + 0.09

0.7A 0.3a

F1 genotypes:

Gametes:

Hardy-Weinberg Application(STOPPED Here)

• In a population of 1000 individuals, 40 have attached earlobes. Recall that the attached earlobe phenotype is a recessive condition.

Required:

(1) Calculate p and q.

(2) How many are heterozygous (Aa)?

Solution• We are given that (40/1000) is the frequency of the homozygous condition, aa.

Recall that p2(AA) + 2pq(Aa) + q2(aa) =1

q2 = frequency of aa individuals = .04. Therefore,

(q2)1/2 = q = .20

p = 1-q = (1 - .2) = .80

Heterozygous frequency = 2pq = 2(.8)(.2) = .32

1000 x .32 = 320 are Aa

How many would be genotypically AA?

Some Practice Problems

• http://nhscience.lonestar.edu/biol/hwe/q1d.html

• Do the first two problems.

No Change through

Generations

STARTING POPULATION

490 AA butterfliesDark-blue wings

420 Aa butterfliesMedium-blue wings

90 aa butterfliesWhite wings

490 AA butterflies

THE NEXT GENERATION

420 Aa butterflies

90 aa butterflies

THE NEXT GENERATION

490 AA butterflies

420 Aa butterflies

90 aa butterflies

NO CHANGE

NO CHANGE

Natural Selection

• A difference in the survival and

reproductive success of different

phenotypes

• Acts directly on phenotypes and indirectly

on genotypes

Reproductive Capacity & Competition

• All populations have the capacity to increase in numbers

• No population can increase indefinitely

• Eventually the individuals of a population will end up competing for resources

Variation in Populations

• All individuals have the same genes that specify the same assortment of traits

• Most genes occur in different forms (alleles) that produce different phenotypes

• Some phenotypes compete better than others

Change over Time

• Over time, the alleles that produce the most successful phenotypes will increase in the population

• Less successful alleles will become less common

• Change leads to increased fitness– Increased adaptation to environment

Results of Natural Selection

Three possible outcomes:

• A shift in the range of values for a given trait in some direction

• Stabilization of an existing range of values

• Disruption of an existing range of values

Directional Selection

• Allele frequencies shift in one direction

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Range of values for the trait at time 1

Range of values for the trait at time 2

Range of values for the trait at time 3

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Revisit the Cane Toad….

• Cane toads in Australia develop longer legs: study

• LONDON (Reuters) - Cane toads in Australia have developed longer legs to enable them to invade more territory, scientists said on Wednesday.

Faster Toads

• Toads with longer legs are faster and are leading the invasion into new territory.

• These longer legged toads are faster.

• What other advantage would speed impart to these toads?

Peppered Moths

• Prior to industrial revolution, most common phenotype was light colored

• After industrial revolution, dark phenotype became more common

Pre-Industrial Population

Peppered Moth on Bark

Light Colored Form on Dark Bark

Result of Genes Interacting with Environment

Pesticide Resistance

• Pesticides kill susceptible insects

• Resistant insects survive and reproduce

• If resistance has heritable basis, it becomes more common with each generation

Pesticide Resistant Insects

Pesticide Resistance in Crops

Global Problem

Antibiotic Resistance

• First came into use in the 1940s

• Overuse has led to increase in resistant forms

• Most susceptible cells died out and were replaced by resistant forms

Resistance Transfer

Antibiotic Resistance

In the News

NDM-1 superbug enzyme's 'photofit' taken

The structure of the protein which stops some of medicine's most powerful antibiotics working has been determined by researchers.

Bacteria which make NDM-1 are of growing concern to health professionals.The protein has larger "jaws" which allow it to attack more antibiotics than other enzymes.

The NDM-1 enzyme, in red, breaking down an antibiotic in blue.

http://www.bbc.co.uk/news/health-14788046By James Gallagher Health reporter, BBC News 6 September 2011

Stabilizing Selection

• Intermediate forms are favored and extremes are eliminated

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Range of values for the trait at time 1

Range of values for the trait at time 2

Range of values for the trait at time 3

Selection for Gall Size

• Gall-making fly has two major predators

• Wasps prey on larvae in small galls

• Birds eat larvae in large galls

• Flies that cause intermediate-sized galls have the highest fitness

Disruptive Selection

• Forms at both ends of the range of variation are favored

• Intermediate forms are selected against

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Range of values for the trait at time 1

Range of values for the trait at time 2

Range of values for the trait at time 3

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African Finches

• Selection favors birds with very large or very small bills

• Birds with intermediate-sized bill are less effective feeders

10

20

30

40

50

60

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10 12.8 15.7 18.5

Widest part of lower bill(millimeters)

nestlings

drought survivors

Sexual Selection

• Selection favors certain secondary sexual characteristics

• Through nonrandom mating, alleles for preferred traits increase

• Leads to increased sexual dimorphism

Elephant Seals - Harems

Balanced Polymorphism

• Polymorphism - “having many forms”

• Occurs when two or more alleles are maintained at frequencies greater than 1 percent

Sickle-Cell Trait: Heterozygote Advantage

• Allele HbS causes sickle-cell anemia when heterozygous

• Heterozygotes are more resistant to malaria than homozygotes

less than 1 in 1,600

1 in 400-1,600

1 in 180-400

1 in 100-180

1 in 64-100

more than 1 in 64

Malaria case

Sickle-cell trait

Gene Flow

• Physical flow of alleles into a population

• Tends to keep the gene pools of populations similar

• Counters the differences that result from mutation, natural selection, and genetic drift

Genetic Drift

• Random change in allele frequencies brought about by chance

• Effect is most pronounced in small populations

• Sampling error - Fewer times an event occurs, greater the variance in outcome

Computer Simulation

AA in five populations

allele A lostfrom fourpopulations

1.0

0.5

01 505 10 15 20 25 30 35 40 45

Generation (25 stoneflies at the start of each)

Computer Simulation

allele A neitherlost norfixed

1.0

0.5

01 505 10 15 20 25 30 35 40 45

Generation (500 stoneflies at the start of each)

Bottleneck

• A severe reduction in population size

• Causes pronounced drift

• Example – Elephant seal population hunted down to just

20 individuals – Population rebounded to 30,000– Electrophoresis revealed there is now no

allele variation at 24 genes

Bottleneck Effect

• All Cheetahs are closely related as a result of a recent bottleneck.

Founder Effect

• Effect of drift when a small number of individuals starts a new population

• By chance, allele frequencies of founders may not be same as those in original population

• Effect is pronounced on isolated islands

Catalina Island Fox

Inbreeding

• Nonrandom mating between related individuals

• Leads to increased homozygosity

• Can lower fitness when deleterious recessive alleles are expressed

• Amish, cheetahs

Atavistic Structures

• “Atavistic structures in individual members of a species arise from a defect in the individual's genetic development. A gene may not turn on (or off) at the right time.”

• Combined with inbreeding, unusual genetic patterns may immerge.

Imagine…

• A human population that:– Have tails– Fully covered with hair (fur)– Walk on all fours – Genetic basis

Human Tails• J Neurosurg. 1985 Sep; 63(3): 461-2. Related Articles, Links

–The human tail: a benign stigma. Case report.

Spiegelmann R, Schinder E, Mintz M, Blakstein A.

Thirty-three cases of true human tails have been reported in the modern English literature. A new case is described and its radiological and pathological features are presented. A review of the literature and analysis of the pathological characteristics of this interesting lumbosacral stigma indicate that the true human tail is a benign condition not associated with any underlying cord malformation.

Publication Types: – Case Reports

–PMID: 3894599 [PubMed - indexed for MEDLINE]

Child with a Tail

Indian Journal of Pediatrics2002 September; 69(9)Islam MK.Dept. of Paediatric Surgery, Sylhet MAG Osmani Medical

College, Bangladesh. mkislam@gononet.comAbstract An interesting case of a child with a tail is reported. The child

had a tail like structure in the back since birth, increasing with age. It was 20 cm. long, the longest tail so far described in the English literature. There was no functional complaint. The result was excellent after excision as the problem was only cosmetic.

Human Tail 1901 Photos

from Harrison, R.G. Occurrence of tails in man, with a description of a case reported by Dr. Watson. Johns Hopkins Hosp. Bull.12:96-101, 1901.

“Walking on all fours with the ancestors “ …BBC (March 07, 2006

)• “FIVE brothers and sisters who can only walk

naturally on all fours are being hailed as a unique insight into human evolution, after being found in a remote corner of rural Turkey.”

• Genetic basis• Siblings have a unique• language• Missing link? (Probably not)

Hirsutism• CASE REPORT• BARBER-SAY SYNDROME: FURTHER DELINEATION OF THE CLINICAL SPECTRUM •   • Fanny M. Cortés, Ledia A. Troncoso, Angélica R. Alliende and Bianca L. Curotto

Unidad de Genética y Enfermedades Metabólicas, Instituto de Nutrición y Tecnología de los Alimentos (INTA), Universidad de Chile, Macul 5540, Santiago, Chile. Send correspondence to F.M.C.

•   •  • ABSTRACT • We report on a 14-year-old girl who presented a multiple congenital anomaly pattern:

ablepharon, hypertelorism, telecanthus, macrostomia, helix agenesis of both ears, redundant thick skin and severe hirsutism, the 5th reported case of Barber-Say syndrome. Our patient had almost the same phenotype as that of the patient cited by Martínez Santana et al. (Am. J. Med. Genet. 47: 20-23, 1993) including the same until then undescribed dermatoglyphic pattern.

•  

BARBER-SAY SYNDROME

Lavinia Fontana[Italian Painter, 1552-1614]

Portrait of a Girl Covered in Hair