chapter 13 how populations evolve · fossils are the imprints or remains of organisms ... –...

© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko

PowerPoint Lectures for

Campbell Biology: Concepts & Connections, Seventh Edition

Reece, Taylor, Simon, and Dickey

Chapter 13 How Populations Evolve

The blue-footed booby has adaptations that make it

suited to its environment. These include

– webbed feet,

– streamlined shape that minimizes friction when it dives,

and

– a large tail that serves as a brake.

Introduction

© 2012 Pearson Education, Inc.

Figure 13.0_1

Figure 13.0_2

Chapter 13: Big Ideas

Darwin’s Theory

of Evolution

The Evolution of

Populations

Mechanisms of

Microevolution

Figure 13.0_3

DARWIN’S THEORY OF EVOLUTION


A five-year voyage around the world helped Darwin

make observations that would lead to his theory of

evolution, the idea that Earth’s many species are

descendants of ancestral species that were

different from those living today.

13.1 A sea voyage helped Darwin frame his theory of evolution


Some early Greek philosophers suggested that life

might change gradually over time.

– However, the Greek philosopher Aristotle viewed

species as perfect and unchanging.

– Judeo-Christian culture reinforced this idea with a literal

interpretation of the biblical book of Genesis.

Fossils are the imprints or remains of organisms

that lived in the past.

In the century prior to Darwin, fossils suggested

that species had indeed changed over time.




In the early 1800s, Jean Baptiste Lamarck suggested that life on Earth evolves, but by a different mechanism than that proposed by Darwin.

Lamarck proposed that

– organisms evolve by the use and disuse of body parts and

– these acquired characteristics are passed on to offspring.


Video: Galápagos Marine Iguana

Video: Galápagos Island Overview

Video: Albatross Courtship Ritual

Video: Soaring Hawk

Video: Galápagos Tortoise

Video: Galápagos Sea Lion

Video: Blue-footed Boobies Courtship Ritual

13_01BMarineIguana_SV.mpg

13_01CGalapagosIslands_SV.mpg

13_01CAlbatrossCourtship_SV.mpg

13_01CSoaringHawk_SV.mpg

13_01ATortoise_SV.mpg

13_01CSeaLion_SV.mpg

13_01CBoobiesCourtship_SV.mpg

During Darwin’s round-the-world voyage he was

influenced by Lyell’s Principles of Geology,

suggesting that natural forces

– gradually changed Earth and

– are still operating today.

Darwin came to realize that

– the Earth was very old and

– over time, present day species have arisen from

ancestral species by natural processes.



During his voyage, Darwin

– collected thousands of plants and animals and

– noted their characteristics that made them well suited to

diverse environments.



Figure 13.1A

Figure 13.1B

Figure 13.1C

Darwin in 1840

NorthAmerica

Pinta

GenovesaMarchena

Santiago Equator

Daphne Islands

SantaFe

SantaCruz

PinzónFernandina

Isabela

Florenza Española0

0 40 miles

40 km

SanCristobal

PACIFICOCEAN

GalápagosIslands

GreatBritain Europe

Asia

HMS Beagle in port

Equator

Africa

PACIFICOCEAN

ATLANTICOCEAN

SouthAmerica

Cape ofGood HopePACIFIC

OCEAN

Cape Horn

Tierra del Fuego

Australia

Tasmania

NewZealand

Figure 13.1C_1

NorthAmerica

GreatBritain Europe Asia

Equator

AfricaPACIFICOCEAN

ATLANTICOCEAN

SouthAmerica

Cape ofGood HopePACIFIC

OCEAN

Cape Horn

Tierra del Fuego

Australia

Tasmania

NewZealand

In 1859, Darwin published On the Origin of Species by Means of Natural Selection,

– presenting a strong, logical explanation of descent with modification, evolution by the mechanism of natural selection, and

– noting that as organisms spread into various habitats over millions of years, they accumulated diverse adaptations that fit them to specific ways of life in these new environments.



Darwin devoted much of The Origin of Species to

exploring adaptations of organisms to their

environment.

Darwin discussed many examples of artificial

selection, in which humans have modified species

through selection and breeding.

13.2 Darwin proposed natural selection as the mechanism of evolution


Figure 13.2

Brussels sprouts

Lateralbuds Terminal bud

Flowersand stems

Cabbage

Broccoli

Stem

KohlrabiWild mustard

Leaves

Kale

Darwin recognized the connection between

– natural selection and

– the capacity of organisms to overreproduce.

Darwin had read an essay written in 1798 by the economist Thomas Malthus, who argued that human suffering was the consequence of human populations increasing faster than essential resources.



Darwin observed that organisms

– vary in many traits and

– produce more offspring than the environment can

support.



Darwin reasoned that

– organisms with traits that increase their chance of

surviving and reproducing in their environment tend to

leave more offspring than others and

– this unequal reproduction will lead to the accumulation

of favorable traits in a population over generations.



There are three key points about evolution by

natural selection that clarify this process.

1. Individuals do not evolve: populations evolve.

2. Natural selection can amplify or diminish only heritable

traits. Acquired characteristics cannot be passed on to

offspring.

3. Evolution is not goal directed and does not lead to

perfection. Favorable traits vary as environments

change.



Camouflage adaptations in insects that evolved in

different environments are examples of the results

of natural selection.

13.3 Scientists can observe natural selection in action


Video: Seahorse Camouflage

13_03ASeaHorses_SV.mpg

Figure 13.3A

A flowermantid inMalaysia

A leaf mantid in Costa Rica

Biologists have documented natural selection in action in

thousands of scientific studies.

Rosemary and Peter Grant have worked on Darwin’s

finches in the Galápagos for over 30 years. They found that

– in wet years, small seeds are more abundant and small beaks are

favored, but

– in dry years, large strong beaks are favored because all seeds are

in short supply and birds must eat more larger seeds.



Another example of natural selection in action is the

evolution of pesticide resistance in insects.

– A relatively small amount of a new pesticide may kill 99%

of the insect pests, but subsequent sprayings are less

effective.

– Those insects that initially survived were fortunate

enough to carry alleles that somehow enable them to

resist the pesticide.

– When these resistant insects reproduce, the percentage

of the population resistant to the pesticide increases.



Figure 13.3B

Pesticideapplication

Chromosome withallele conferringresistance to pesticide

Additional applications of thesame pesticide will be less effective,and the frequency of resistantinsects in the population will grow.

Survivors

These examples of evolutionary adaptation highlight two important points about natural selection.

1. Natural selection is more of an editing process than a creative mechanism.

2. Natural selection is contingent on time and place, favoring those characteristics in a population that fit the current, local environment.



Darwin’s ideas about evolution also relied on the fossil record, the sequence in which fossils appear within strata (layers) of sedimentary rocks.

Paleontologists, scientists who study fossils, have found many types of fossils.

13.4 The study of fossils provides strong evidence for evolution


Figure 13.4A

Skull ofHomo erectus

Figure 13.4B

Ammonite casts

Figure 13.4C

Dinosaur tracks

Figure 13.4D

Fossilized organic matter of a leaf

Figure 13.4E

Insect in amber

Figure 13.4F

“Ice Man”

The fossil record shows that organisms have evolved in a historical sequence.

– The oldest known fossils, extending back about 3.5 billion years ago, are prokaryotes.

– The oldest eukaryotic fossils are about a billion years younger.

– Another billion years passed before we find fossils of multicellular eukaryotic life.



Video: Grand Canyon

13_04GGrandCanyon_SV.mpg

Figure 13.4G

Many fossils link early extinct species with species

living today.

– A series of fossils traces the gradual modification of

jaws and teeth in the evolution of mammals from a

reptilian ancestor.

– A series of fossils documents the evolution of whales

from a group of land mammals.



Figure 13.4H

Pakicetus (terrestrial)

Rodhocetus (predominantly aquatic)

Dorudon (fully aquatic)

Pelvis andhind limb

Pelvis andhind limb

Balaena (recent whale ancestor)

13.5 Many types of scientific evidence support the evolutionary view of life

Biogeography, the geographic distribution of

species, suggested to Darwin that organisms

evolve from common ancestors.

Darwin noted that Galápagos animals resembled

species on the South American mainland more

than they resembled animals on islands that were

similar but much more distant.



Comparative anatomy

– is the comparison of body structures in different species,

– was extensively cited by Darwin, and

– illustrates that evolution is a remodeling process.

– Homology is the similarity in characteristics that result

from common ancestry.

– Homologous structures have different functions but

are structurally similar because of common ancestry.


Figure 13.5A

Humerus

Radius

Ulna

Carpals

Metacarpals

Phalanges

Human Cat Whale Bat

Comparative embryology

– is the comparison of early stages of development among

different organisms and

– reveals homologies not visible in adult organisms.

– For example, all vertebrate embryos have, at some point

in their development,

– a tail posterior to the anus and

– pharyngeal throat pouches.

– Vestigial structures are remnants of features that

served important functions in an organism’s ancestors.



Figure 13.5B

Pharyngeal

pouches

Post-analtail

Chickembryo

Humanembryo

Figure 13.4H_2

Pelvis andhind limb

Balaena (recent whale ancestor)

Advances in molecular biology reveal evolutionary

relationships by comparing DNA and amino acid

sequences between different organisms. These

studies indicate that

– all life-forms are related,

– all life shares a common DNA code for the proteins found

in living cells, and

– humans and bacteria share homologous genes that have

been inherited from a very distant common ancestor.



Darwin was the first to represent the history of life as a tree,

– with multiple branchings from a common ancestral trunk

– to the descendant species at the tips of the twigs.

Today, biologists

– represent these patterns of descent with an evolutionary tree, but

– often turn the trees sideways.

13.6 Homologies indicate patterns of descent that can be shown on an evolutionary tree


Homologous structures can be used to determine the branching sequence of an evolutionary tree. These homologies can include

– anatomical structure and/or

– molecular structure.

– Figure 13.6 illustrates an example of an evolutionary tree.

13.6 Homologies indicate patterns of descent that can be shown on an evolutionary tree


Figure 13.6

Tetrapodlimbs

Amnion

Lungfishes

Amphibians

Mammals

Lizardsand snakes

Crocodiles

Ostriches

Hawks andother birds

Feathers

Tetra

po

ds

Am

nio

tes

Bird

s

1

2

3

4

5

6

THE EVOLUTION OF

POPULATIONS


13.7 Evolution occurs within populations

A population is

– a group of individuals of the same species and

– living in the same place at the same time.

Populations may be isolated from one another (with little interbreeding).

Individuals within populations may interbreed.

We can measure evolution as a change in heritable traits in a population over generations.


Figure 13.7

A gene pool is the total collection of genes in a

population at any one time.

Microevolution is a change in the relative

frequencies of alleles in a gene pool over time.



Population genetics studies how populations

change genetically over time.

The modern synthesis connects Darwin’s theory

with population genetics.



Organisms typically show individual variation.

However, in The Origin of Species, Darwin could

not explain

– the cause of variation among individuals or

– how variations were passed from parents to offspring.

13.8 Mutation and sexual reproduction produce the genetic variation that makes evolution possible


Figure 13.8

Mutations are

– changes in the nucleotide sequence of DNA and

– the ultimate source of new alleles.



On rare occasions, mutant alleles improve the

adaptation of an individual to its environment.

– This kind of effect is more likely when the environment is

changing such that mutations that were once

disadvantageous are favorable under new conditions.

– The evolution of DDT-resistant houseflies is such an

example.



Chromosomal duplication is an important source of

genetic variation.

– If a gene is duplicated, the new copy can undergo

mutation without affecting the function of the original

copy.

– For example, an early ancestor of mammals had a

single gene for an olfactory receptor. That gene has

been duplicated many times, and mice now have 1,300

different olfactory receptor genes.



Sexual reproduction shuffles alleles to produce

new combinations in three ways.

1. Homologous chromosomes sort independently as they

separate during anaphase I of meiosis.

2. During prophase I of meiosis, pairs of homologous

chromosomes cross over and exchange genes.

3. Further variation arises when sperm randomly unite with

eggs in fertilization.



Animation: Genetic Variation from Sexual Recombination

13_08SexualRecombination_A.html

13.9 The Hardy-Weinberg equation can test whether a population is evolving

Sexual reproduction alone does not lead to

evolutionary change in a population.

– Although alleles are shuffled, the frequency of alleles

and genotypes in the population does not change.

– Similarly, if you shuffle a deck of cards, you will deal out

different hands, but the cards and suits in the deck do

not change.


The Hardy-Weinberg principle states that

– within a sexually reproducing, diploid population,

– allele and genotype frequencies will remain in equilibrium,

– unless outside forces act to change those frequencies.



For a population to remain in Hardy-Weinberg

equilibrium for a specific trait, it must satisfy five

conditions. There must be

1. a very large population,

2. no gene flow between populations,

3. no mutations,

4. random mating, and

5. no natural selection.



Imagine that there are two alleles in a blue-footed

booby population, W and w.

– Uppercase W is a dominant allele for a nonwebbed

booby foot.

– Lowercase w is a recessive allele for a webbed booby

foot.



Figure 13.9A

Webbing No webbing

Consider the gene pool of a population of 500

boobies.

– 320 (64%) are homozygous dominant (WW).

– 160 (32%) are heterozygous (Ww).

– 20 (4%) are homozygous recessive (ww).

– p = 80% of alleles in the booby population are W.

– q = 20% of alleles in the booby population are w.



Figure 13.9B

Phenotypes

Genotypes

Number of animals

(total 500)

Genotype frequencies

Allele frequencies

Number of alleles

in gene pool

(total 1,000)

0.8 W 0.2 w

40 w640 W 160 W 160 w

WwWW ww

20160320

0.64 0.32 0.04

320500 500

160 20500

800 2001,0001,000

The frequency of all three genotypes must be

100% or 1.0.

– p2 + 2pq + q2 = 100% = 1.0

– homozygous dominant (p2) + heterozygous (2pq) +

homozygous recessive (q2) = 100%



What about the next generation of boobies?

– The probability that a booby sperm or egg carries W = 0.8 or 80%.

– The probability that a sperm or egg carries w = 0.2 or 20%.

– The genotype frequencies will remain constant generation after generation unless something acts to change the gene pool.



Figure 13.9C

Gametes reflect allelefrequencies of parentalgene pool.

Sperm

Eggs

WW Ww

wwwW

W

W w

w

Next generation:

Genotype frequencies

Allele frequencies 0.2 w0.8 W

0.64 WW 0.32 Ww 0.04 ww

q 0.2

p 0.8

p2 0.64 pq 0.16

qp 0.16 q2 0.04

p 0.8 q 0.2

How could the Hardy-Weinberg equilibrium be

disrupted?

– Small populations could increase the chances that allele

frequencies will fluctuate by chance.

– Individuals moving in or out of populations add or remove

alleles.

– Mutations can change or delete alleles.

– Preferential mating can change the frequencies of

homozygous and heterozygous genotypes.

– Unequal survival and reproductive success of individuals

(natural selection) can alter allele frequencies.



Public health scientists use the Hardy-Weinberg

equation to estimate frequencies of disease-

causing alleles in the human population.

One out of 10,000 babies born in the United States

has phenylketonuria (PKU), an inherited inability to

break down the amino acid phenylalanine.

Individuals with PKU must strictly limit the intake of

foods with phenylalanine.

13.10 CONNECTION: The Hardy-Weinberg equation is useful in public health science


Figure 13.10

INGREDIENTS: SORBITOL,

MAGNESIUM STEARATE,

ARTIFICIAL FLAVOR,

ASPARTAME† (SWEETENER),

ARTIFICIAL COLOR

(YELLOW 5 LAKE, BLUE 1

LAKE), ZINC GLUCONATE.

†PHENYLKETONURICS:

CONTAINS PHENYLALANINE

PKU is a recessive allele.

The frequency of individuals born with PKU

corresponds to the q2 term in the Hardy-Weinberg

equation and would equal 0.0001.

– The value of q is 0.01.

– The frequency of the dominant allele would equal 1 – q,

or 0.99.

– The frequency of carriers

= 2pq

= 2 0.99 0.01 = 0.0198 = 1.98% of the U.S. population.

13.10 CONNECTION: The Hardy-Weinberg equation is useful in public health science


MECHANISMS

OF MICROEVOLUTION


13.11 Natural selection, genetic drift, and gene flow can cause microevolution

If the five conditions for the Hardy-Weinberg

equilibrium are not met in a population, the

population’s gene pool may change. However,

– mutations are rare and random and have little effect on

the gene pool, and

– nonrandom mating may change genotype frequencies

but usually has little impact on allele frequencies.



The three main causes of evolutionary change are

1. natural selection,

2. genetic drift, and

3. gene flow.



1. Natural selection

– If individuals differ in their survival and reproductive

success, natural selection will alter allele frequencies.

– Consider the imaginary booby population. Webbed

boobies (ww) might

– be more successful at swimming,

– capture more fish,

– produce more offspring, and

– increase the frequency of the w allele in the gene pool.



2. Genetic drift

– Genetic drift is a change in the gene pool of a

population due to chance.

– In a small population, chance events may lead to the

loss of genetic diversity.



2. Genetic drift, continued

– The bottleneck effect leads to a loss of genetic diversity

when a population is greatly reduced.

– For example, the greater prairie chicken once numbered in the

millions, but was reduced to about 50 birds in Illinois by 1993.

– A survey comparing the DNA of the surviving chickens with

DNA extracted from museum specimens dating back to the

1930s showed a loss of 30% of the alleles.


Animation: Causes of Evolutionary Change

13_11AEvolutionaryChanges_A.html

Figure 13.11A_s1

Originalpopulation

Figure 13.11A_s2

Originalpopulation

Bottleneckingevent

Figure 13.11A_s3

Originalpopulation

Bottleneckingevent

Survivingpopulation

Figure 13.11B

2. Genetic drift, continued

– Genetic drift also results from the founder effect, when

a few individuals colonize a new habitat.

– A small group cannot adequately represent the genetic

diversity in the ancestral population.

– The frequency of alleles will therefore be different between the

old and new populations.



3. Gene flow

– is the movement of individuals or gametes/spores

between populations and

– can alter allele frequencies in a population.

– To counteract the lack of genetic diversity in the

remaining Illinois greater prairie chickens,

– researchers added 271 birds from neighboring states to the

Illinois populations, which

– successfully introduced new alleles.



13.12 Natural selection is the only mechanism that consistently leads to adaptive evolution

Genetic drift, gene flow, and mutations could each result in microevolution, but only by chance could these events improve a population’s fit to its environment.

Natural selection is a blend of

– chance and

– sorting.

Because of this sorting, only natural selection consistently leads to adaptive evolution.


13.12 Natural selection is the only mechanism that consistently leads to adaptive evolution

An individual’s relative fitness is the contribution it

makes to the gene pool of the next generation

relative to the contribution of other individuals.

The fittest individuals are those that

– produce the largest number of viable, fertile offspring and

– pass on the most genes to the next generation.


Figure 13.12

Natural selection can affect the distribution of

phenotypes in a population.

– Stabilizing selection favors intermediate phenotypes,

acting against extreme phenotypes.

– Directional selection acts against individuals at one of

the phenotypic extremes.

– Disruptive selection favors individuals at both extremes

of the phenotypic range.

13.13 Natural selection can alter variation in a population in three ways


Figure 13.13

Originalpopulation

Evolvedpopulation

Phenotypes(fur color)

Fre

qu

en

cy o

fin

div

idu

als

Originalpopulation

Stabilizing selection Directional selection Disruptive selection

13.14 Sexual selection may lead to phenotypic differences between males and females

Sexual selection

– is a form of natural selection

– in which individuals with certain characteristics are more

likely than other individuals to obtain mates.

In many animal species, males and females show

distinctly different appearances, called sexual

dimorphism.

Intrasexual selection (within the same sex) involves

competition for mates, usually by males.


Figure 13.14A

Figure 13.14B

13.14 Sexual selection may lead to phenotypic differences between males and females

In intersexual selection (between sexes) or mate

choice, individuals of one sex (usually females)

– are choosy in picking their mates and

– often select flashy or colorful mates.


Figure 13.14C

The excessive use of antibiotics is leading to the

evolution of antibiotic-resistant bacteria.

As a result, natural selection is favoring bacteria

that are naturally resistant to antibiotics.

– Natural selection for antibiotic resistance is particularly

strong in hospitals.

– Methicillin-resistant (MRSA) bacteria can cause “flesh-

eating disease” and potentially fatal infections.

13.15 EVOLUTION CONNECTION: The evolution of antibiotic resistance in bacteria is a serious public health concern


Figure 13.15

What prevents natural selection from eliminating

unfavorable genotypes?

– In diploid organisms, recessive alleles are usually not

subject to natural selection in heterozygotes.

– Balancing selection maintains stable frequencies of

two or more phenotypes in a population.

– In heterozygote advantage, heterozygotes have greater

reproductive success than homozygotes.

– Frequency-dependent selection is a type of balancing

selection that maintains two different phenotypes in a

population.

13.16 Diploidy and balancing selection preserve genetic variation


Figure 13.16

“Left-mouthed”

“Right-mouthed”

Fre

qu

en

cy o

f

“le

ft-m

ou

thed”

ind

ivid

uals

Sample year

1981 ʼ82 ʼ83 ʼ84 ʼ85 ʼ86 ʼ87 ʼ88 ʼ89 ʼ900

0.5

1.0

The evolution of organisms is constrained.

1. Selection can act only on existing variations. New,

advantageous alleles do not arise on demand.

2. Evolution is limited by historical constraints. Evolution

co-opts existing structures and adapts them to new

situations.

3. Adaptations are often compromises. The same

structure often performs many functions.

4. Chance, natural selection, and the environment interact.

Environments often change unpredictably.

13.17 Natural selection cannot fashion perfect organisms


Figure 13.UN04

change in allelefrequencies in a

population

Microevolution

may result from

is the

randomfluctuations

more likely in a

due tomovement

ofdueto

leadsto

(c)(b)(a)

ofindividuals

may beresult of

(d) (g)

(f)(e)

individualsor gametes

adaptiveevolution

best adaptedto environment

Concept Check

The similarity in bone structure and arrangement between cats and bats

suggests that

– bats originated from bird-like ancestors.

– bats originated from four-legged ancestors, such as cats.

– modern bats fly much faster than ancient bat species.


Answer

The similarity in bone structure and arrangement between

cats and bats suggests that

b) bats originated from four-legged ancestors, such as cats.


Concept Check

Darwin proposed the theory of natural selection as the mechanism of

evolution based on three observations about nature. Which of the

following were part of Darwin’s observations?

– Populations have the potential to produce more individuals than the

environment can support.

– Individuals in some populations have varied characteristics.

– Variation in individuals appears to be inherited.

– All of the above.


Answer

Darwin proposed the theory of natural selection as the mechanism of

evolution based on three observations about nature. Which of the

following were part of Darwin’s observations?

d) All of the above.


Concept Check

Natural selection acts on genetic

variation. The ultimate source of

genetic variation is mutation in the DNA

(or RNA is some organisms). However

in sexually reproducing organisms with

long generation time what process(es)

account(s) for individual variation?

– random fertilization

– crossing over

– independent assortment

– all of the above


Answer

Natural selection acts on genetic

variation. The ultimate source of

genetic variation is mutation in the DNA

(or RNA is some organisms). However

in sexually reproducing organisms with

long generation time what process(es)

account(s) for individual variation?

d) all of the above


Concept Check

Evolutionary fitness is an often misunderstood concept. Which of the

following imaginary individuals would have the greatest evolutionary fitness?

– Sparrow A

– Sparrow B

– Sparrow C

– Sparrow D


Sparrow A Sparrow B Sparrow C Sparrow D

Beak size (mm) 13 15 17 16

Lifespan (years) 2.5 2 3 3

Offspring that

survive to

adulthood

10 16 12 14

Answer

Evolutionary fitness is an often misunderstood concept. Which of the

following imaginary individuals would have the greatest evolutionary fitness?

b) Sparrow B


Sparrow A Sparrow B Sparrow C Sparrow D

Beak size (mm) 13 15 17 16

Lifespan (years) 2.5 2 3 3

Offspring that

survive to

adulthood

10 16 12 14

Interpreting Data

The figure above shows the frequency of foot phenotypes in a

population of blue-footed boobies. What is the frequency of the W allele

in this population?

– 0.2

– 0.4

– 0.5

– 0.6


Answer


population of blue-footed boobies. What is the frequency of the W allele

in this population?

c) 0.5


Interpreting Data

The figure above shows the frequency of foot phenotypes in a population of blue-footed boobies. What is the frequency of the w allele in this population?

– 0.2

– 0.4

– 0.5

– 0.6


Answer

The figure above shows the frequency of foot phenotypes in a population of blue-footed boobies. What is the frequency of the w allele in this population?

c) 0.5


Interpreting Data

The figure above shows the frequency of foot phenotypes in a population of blue-footed boobies. What is the expected frequency of the WW genotype in this population assuming the population is in Hardy-Weinberg equilibrium (Hint: The frequency of W is 0.5 and the frequency of w is 0.5.)?

– 0.20

– 0.25

– 0.40

– 0.50


Answer

The figure above shows the frequency of foot phenotypes in a population of blue-footed boobies. What is the expected frequency of the WW genotype in this population assuming the population is in Hardy-Weinberg equilibrium (Hint: The frequency of W is 0.5 and the frequency of w is 0.5.)?

b) 0.25


Interpreting Data


population of blue-footed boobies. Is this population in Hardy-Weinberg

equilibrium?

– Yes

– No


Answer


population of blue-footed boobies. Is this population in Hardy-Weinberg

equilibrium?

b) No


Biology and Society

One concept of conservation biology is known as minimum viable population. Some species’ populations are so fragmented and small that they may have very little genetic variability left. With minimal genetic variation in the population there is little likelihood that a population can adapt to an environmental threat, such as a new disease. Florida panthers are at or below the minimum viable population level (estimated population less than 80).

Do you think that it is practical to use limited resources to conserve a population like the Florida panther?


Disagree Agree

Strongly A B C D E Strongly

Biology and Society

During the anthrax crisis of 2001, public health officials urged citizens to not take the antibiotic ciprofloxacin as a preventative measure. Public health officials were concerned that over use of ciprofloxacin would lead to resistant varieties of anthrax and other bacterial pathogens. Ciprofloxacin is one of the few readily available effective antibiotics that can treat anthrax.

Do you think that public health officials should more directly regulate the availability of ciprofloxacin to assure its proper use?


Disagree Agree


Biology and Society

For some, science and religion seem to be at odds—especially with

regard to the topic of evolution. Many evolutionary scientists hold

devout religious beliefs. Like many devoutly religious people these

scientists are able to reconcile their religion and their science. Others

find the two ways of knowing to be in conflict. There is little doubt that a

literate citizen should explore the interface between science and

religion. There is a social controversy but there is not a scientific

controversy.

Do you think that this issue should be a part of a science class?


Disagree Agree


Concept Review

The Mammals that Conquered the Seas

• Fossil evidence indicates that vertebrates originated in

aquatic environments and later adapted to land.

• Mammals originated on land. But some mammals, such

as whales, later adapted to marine environments,

reversing the trend.

Concept Review


• Whales may live in water, but they are not fish.

• They are clearly warm-blooded mammals, breathing air

and nursing their young. Along with dolphins and porpoises,

they belong to an order of mammals called cetacea.

• The whales’ return to water was poorly understood until

fossil discoveries over the last two decades helped trace their

transition.

Concept Review


• This shift occurred during the Eocene era, about 55

to 34 million years ago.

• Archaic whales, or archaeocetes, may have been drawn

back to aquatic life by ancient seas teeming with food.

Concept Review


• Whales’ transitional ancestors had characteristics of both

land and sea creatures – legs and hooves for walking, tails

for swimming.

Concept Review


• But later fossil and molecular studies suggest closer ties

to artiodactyls, even-toed hoofed mammals such as

camels and pigs.

• The hippopotamus may be an especially close whale

relative.

• Scientists once thought whales might be descended from

extinct wolf-like hoofed mammals called mesonychids.

Testing Your Comprehension


Distant ancestors of whales had what characteristics?

a) fur

b) milk-producing glands

c) legs and feet

d) all of the above



Distant ancestors of whales had what characteristics?

d) all of the above



Whales are most closely related to which terrestrial mammals?

a) artiodactyls such as camels, pigs, and cows

b) carnivores such as bears, raccoons, and otters

c) perissodactyls such as horses, donkeys, and zebras

d) all of the above



Whales are most closely related to which terrestrial mammals?

a) artiodactyls such as camels, pigs, and cows



Which of the following do not help explain how modern whales

fit into the mammalian family tree?

a) DNA analysis

b) the fossil record

c) modern whale anatomy

d) antibody-antigen physiology



Which of the following do not help explain how modern whales

fit into the mammalian family tree?

c) modern whale anatomy



Which of these is not thought to be an ancestor of modern

whales?

a) Basilosaurus

b) Ambulocetus

c) Orca

d) Dorudon



Which of these is not thought to be an ancestor of modern

whales?

c) Orca

Biology and Society


Selective pressures in the Eocene environment caused whales

to adapt and return to water. Environmental pressures

are also driving natural selection in the present-day world.

Strongly

Agree

Strongly

DisagreeA. E.C.B. D.

Biology and Society


During the Eocene era, ancient oceans covered much of what

is now the Indian subcontinent, including Pakistan. Important

whale ancestor fossils have been found there, but such work

has also been interrupted by modern-day conflict. Scientists

should receive special protection to conduct research globally,

despite political or social problems.

Strongly

Agree

Strongly


Thinking About Science


Most mammals cannot live without fresh water. But

cetaceans obtain their water, in part, from sips of the salty

ocean. To investigate when the ancestors of whales

became able to ingest seawater, scientists applied a

technique to measure the ratio of certain oxygen isotopes

in fossilized teeth. The ratio of these isotopes is different in

fresh and salt water.

Describe how this difference helped shape the hypothesis

of the scientists conducting the research.

Interpreting Data and Graphs


These drawings illustrate how

various hypotheses of whale

ancestry have changed as new

findings come to light.

According to each of the four

drawings, which category of

creature is the whale’s closest

relative?

1. Explain how Darwin’s voyage on the Beagleinfluenced his thinking.

2. Explain how the work of Thomas Malthus and the process of artificial selection influenced Darwin’s development of the idea of natural selection.

3. Describe Darwin’s observations and inferences in developing the concept of natural selection.

4. Explain why individuals cannot evolve and why evolution does not lead to perfectly adapted organisms.

You should now be able to


5. Describe two examples of natural selection known to occur in nature.

6. Explain how fossils form, noting examples of each process.

7. Explain how the fossil record, biogeography, comparative anatomy, and molecular biology support evolution.

8. Explain how evolutionary trees are constructed and used to represent ancestral relationships.

9. Define the gene pool, a population, and microevolution.



10. Explain how mutation and sexual reproduction produce genetic variation.

11. Explain why prokaryotes can evolve more quickly than eukaryotes.

12. Describe the five conditions required for the Hardy-Weinberg equilibrium.

13. Explain why the Hardy-Weinberg equilibrium is significant to understanding the evolution of natural populations and to public health science.



14. Define genetic drift and gene flow. Explain how the bottleneck effect and the founder effect influence microevolution.

15. Distinguish between stabilizing selection, directional selection, and disruptive selection. Describe an example of each.

16. Define and compare intrasexual selection and intersexual selection.

17. Explain how antibiotic resistance has evolved.

18. Explain why natural selection cannot produce perfection.



Concept Review

Founder Mutations

• A founder mutation is a mutation shared by many

individuals because they share a common ancestor.

• Founder mutations associated with disease are often

recessive and spare individuals who carry only one

copy of the mutant gene.

• This makes it possible for the mutation to spread from

the founder to his or her descendants instead of being

eliminated.

• Founder mutations provide a window to human

migrations.

Concept Review

Founder Mutations

• Mutations arise by random changes to DNA

sequences.

• Genes can be mutated to cause inherited disease in

two general ways:

1) Different individuals may carry different mutations in

the gene associated with the disease.

2) Precisely the same mutation may be seen again and

again in a disease-associated gene.

Concept Review

Founder Mutations

• A repeatedly observed disease-causing mutation can

occur if

- A hotspot for mutation is mutated independently in

different individuals.

or

- A mutation occurs in one individual, the founder, and is

transmitted to the founder’s descendants.

Concept Review

Founder Mutations

• Everyone who carries the founder mutation also

shares nearby sequences of DNA.

• This shared DNA region is a haplotype.

• Over time, haplotypes

become progressively shorter

because of recombination

between homologous

chromosomes.

• Therefore, the length of the

haplotype provides an estimate

of how long ago the founder

mutation occurred.

Concept Review

Founder Mutations

Concept Review

Founder Mutations

• Founder mutations are hundreds to thousands of

times more common than typical mutations that cause

disease.

• Founder mutations reach high frequencies through

natural selection because they provide an advantage to

individuals who carry only one copy of the mutated

gene.

• For example, carrying a single copy of the founder

mutation that causes hereditary hemochromatosis

enhances iron absorption, an advantage when diets are

poor in iron.

Concept Review

Founder Mutations

• The frequency of a founder mutation represents a

balance between two competing forces – the harm

caused by carrying two copies of the mutation weighted

against the benefit provided by carrying one copy of the

mutation.

• This is balancing selection.

Concept Review

Founder Mutations

PTC Taste Perception and the Out of Africa Hypothesis

• About 75% of people worldwide perceive the chemical

PTC as extremely bitter; the rest cannot taste it at all.

• The inability to taste PTC is due to a founder mutation.

• In African populations, there are seven different forms

of the gene associated with PTC perception.

• Outside of Africa, there is only one major taster and

one nontaster form of the gene.

Concept Review

Founder Mutations

• The nontaster mutation is in a very short haplotype,

indicating an ancient origin for this mutation.

• Two conclusions can be drawn:

Concept Review

Founder Mutations

• The existence of a single nontaster haplotype is

consistent with the tenet of the Out of Africa hypothesis

that ancestors of modern non-African populations

migrated from Africa about 75,000 years ago. These

migrants carried one major taster and one nontaster

form of the gene.

• The single PTC nontaster mutation suggests that

migrants from Africa did not interbreed with local

populations that almost certainly would have carried

their own unique mutations of this gene.

Concept Review

Founder Mutations

The Hemochromatosis Founder Mutation as a Window

to European Migrations

• The hemochromatosis founder mutation is found at

highest frequencies in Celtic peoples of northwestern

Europe and at lower frequencies in other regions of

Europe.

• The Celts were a dominant group in central Europe

2,000 years ago but were largely displaced north and

west by the expanding Roman Empire.

Concept Review

Founder Mutations

• Did the hemochromatosis founder mutation arise in

central Europe before Celtic migrations? Or did it

originate in today’s Celtic lands and spread

southeastward?

Concept Review

Founder Mutations

• The large size of the haplotype that contains the

hemochromatosis mutation indicates that it originated

recently: 60 to 70 generations ago, or about A.D. 800.

• Because this was long after the displacement of the

Celts from central Europe, the mutation must have

arisen in northwestern Europe and spread

southeastward through the founder’s descendants.

• Analysis of founder mutations offers insight into where

we came from and how we came to inhabit modern

homelands.

Founder Mutations


How many copies of a founder mutation are required to

cause disease?

a) 1

b) 2

c) 4

d) 8

Founder Mutations


How many copies of a founder mutation are required to

cause disease?

b) 2

Founder Mutations


If two people have the same genetic disease caused by

a mutation other than a founder mutation, they usually

will have

a) exactly the same mutation in the same gene

b) different mutations in the same gene

c) hotspot mutations in different genes

d) markedly different symptoms

Founder Mutations


If two people have the same genetic disease caused by

a mutation other than a founder mutation, they usually

will have

b) different mutations in the same gene

Founder Mutations


Over time, haplotypes become

a) shorter

b) longer

c) more harmful

d) less harmful

Founder Mutations


Over time, haplotypes become

a) shorter

Founder Mutations


Balancing selection leads to

a) elimination of founder mutations

b) a continual increase in the frequency of founder

mutations

c) a stable frequency of a founder mutation

d) a fluctuating frequency of a founder mutation

Founder Mutations


Balancing selection leads to

c) a stable frequency of a founder mutation

Founder Mutations

Biology and Society

The investigation of founder mutations and other

markers of human origins shows that human

populations are very closely related. If people could be

educated about their close degree of kinship, this would

help prevent conflicts across the world.

Strongly

Agree

Strongly


Founder Mutations


The figure shows two sets of DNA sequences obtained

from 8 different people. The A shown in red is a disease-

causing mutation. Letters in the blue-bordered columns

are DNA sequences that may vary, but do not cause the

disease. Which set comes from people carrying a

founder mutation?

a) The top set

b) The bottom set

Founder Mutations


The figure shows two sets of DNA sequences obtained

from 8 different people. The A shown in red is a disease-

causing mutation. Letters in the blue-bordered columns

are DNA sequences that may vary, but do not cause the

disease. Which set comes from people carrying a

founder mutation?

b) The bottom set

Interpreting Data and Graphs

Founder Mutations

• DNA sequences of a small part of one gene from a

healthy individual and three individuals with genetic

disease caused by mutations of this gene are shown in

the following table.

Which mutation is likely to cause this disease?

Is this a founder mutation?

Healthy ACCGTAC

Diseased 1 ACTCTAC

Diseased 2 TCCCTAC

Diseased 3 ACCCTAG

chapter 13 how populations evolve · fossils are the imprints or remains of organisms ... –...

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