Chapter 22 Descent with Modification: a Darwinian View of Life

Chapter 22 Descent with Modification: A Darwinian View of Life

Student Guided Notes

Overview: Endless Forms Most Beautiful

On November 24, 1859, Charles Darwin published his hypothesis in ______, ushering in the era of evolutionary biology.
Darwin defined evolution as ______, proposing that Earth’s many species are descendants of ancestral species that were very different from those alive today.

○Evolution can also be defined more narrowly as ______.

Concept 22.1 The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species

Darwin’s hypothesis had its roots in the work of many other individuals.
The Greek philosopher Aristotle (384–322 A.D.) opposed any concept of evolution and viewed species as ______.
______ (1707–1778), a Swedish physician and botanist, developed a ______ system for naming species according to genus and species and classifying species into a hierarchy of increasingly complex categories.
Darwin’s views were influenced by fossils, ______.

○Fossils within layers of ______rock show that a succession of organisms have populated Earth throughout time.

Paleontology, the study of ______, was largely developed by the French anatomist ______ (1769–1832).

○Instead of evolution, Cuvier advocated ______, speculating that boundaries between strata were due to local floods or droughts that destroyed the species then present.

In contrast to Cuvier’s catastrophism, Scottish geologist James Hutton (1726–1797) proposed a theory of gradualism, which held that profound geologic changes took place through the cumulative effect ______.
Later, geologist Charles Lyell (1797–1875) proposed a theory of ______, which held that geologic processes had not changed throughout Earth’s history.
Hutton’s and Lyell’s observations and theories had a strong influence on Darwin.

○If geologic changes result from slow, continuous processes rather than sudden events, then the Earth must be ______estimated by theologians from biblical inference.

In 1809, French biologist ______ (1744–1829) published a theory of evolution.

Lamarck explained his observations with two principles: ______of parts and the ______.

○Use and disuse was the concept that body parts that are used extensively become ______, while those that are not used ______. (he was right on this!!)

○The inheritance of acquired characteristics stated that modifications acquired during the life of an organism ______. (he was wrong on this!!)

○A classic example is the long neck of the giraffe. Lamarck reasoned that the long, muscular neck of the modern giraffe evolved over many generations as the ancestors of giraffes reached for leaves on higher branches and passed this characteristic on to their offspring.

Concept 22.2 Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity of life

When Darwin was 16, his father sent him to the University of ______to study ______.

Darwin left Edinburgh without a degree and enrolled at ______University with the intent of becoming a ______.

○At that time, most naturalists and scientists belonged to the clergy.

After graduation, Darwin joined the crew of the survey ship HMS Beagle as ship naturalist and conversation companion to Captain Robert FitzRoy.

The voyage of the Beagle

Darwin embarked from ______on the Beagle in December ______.
Darwin collected thousands of specimens and noted that the plants and animals of South America were very different from those of Europe.
Darwin also found fossils that were formed by ______similar to one he experienced.

○These observations reinforced Darwin’s acceptance of Lyell’s ideas and led him to doubt the traditional view ______(thought of as 6,000 years old and unchanging.)

Darwin’s interest in the geographic distribution of species was further stimulated by the Beagle’s visit to the ______, a group of young volcanic islands 900 km west of the ______coast.

Darwin’s focus on adaptation

During his travels, Darwin observed many examples of adaptations, ______(ex. finches and differences in beaks related to food they ate).

○Darwin explained that adaptations arise by natural selection______.

By the early 1840s, Darwin had developed the major features of his theory of natural selection as the mechanism for evolution.
In June 1858, ______- (1823–1913), a young naturalist sent Darwin a manuscript containing a hypothesis of ______.
Darwin finished The Origin of Species and published it the next year.
Although both Darwin and Wallace developed similar ideas independently, the theory of evolution by natural selection is attributed to Darwin because he developed his ideas earlier and supported the theory much more extensively.

The Origin of Species

Darwin used the phrase ______ to describe evolution.

○All organisms are related through descent from a common ancestor that ______. As a result, organisms share many characteristics, explaining the ______of life.

○Over evolutionary time, the descendents of that common ancestor have accumulated ______, that allow them to survive and reproduce in specific habitats.

○Over long periods of time, descent with modification has led to the rich ______.

Artificial selection, natural selection, and adaptation

Darwin proposed a mechanism—______—to explain the observable patterns of evolution.
Darwin’s views on the role of environmental factors in the screening of heritable variation were heavily influenced by artificial selection.
Darwin described two observations of nature, from which he drew two inferences.

○Observation #1: ______.

○Observation #2: ______.

○Inference #1: Individuals whose inherited traits give them a ______and reproducing in a given environment than other individuals tend to ______.

○Inference #2: This unequal ability of individuals to survive and reproduce will cause ______.

A 1798 essay on human population by ______ heavily influenced Darwin’s views on “overreproduction.”

○Malthus contended that much human suffering—______—was the inescapable consequence of ______(over-reproduction is characteristic of most species.)

Three important points need to be emphasized about evolution through natural selection.

Although natural selection occurs through interactions between individual organisms and their environment, ______. A ______ is the smallest group that can evolve over time.
Natural selection can act only on ______traits, traits that are passed from organisms to their offspring. Characteristics acquired by an organism during its lifetime may enhance its survival and reproductive success, but there is no evidence that such characteristics can be inherited by offspring.
______factors vary from ______to ______and from time to time. A trait that is favorable in one environment may be ______.

Concept 22.3 Evolution is supported by an overwhelming amount of scientific evidence

Four types of data document the pattern of evolution and tell us about the processes by which it occurs: direct ______, ______, the ______, and ______.

Direct observations of evolutionary change

The evolution of drug resistance is a particular problem in bacteria and viruses, which exhibit rapid rates of reproduction.

Many people harbor the bacterium Staphylococcus aureus on their ______or in their ______with no ______effects.

○Some genetic strains of this species, known as ______(MRSA), are formidable pathogens.

In ______, ______became the first widely used antibiotic.

○By 1945, more than _____% of S. aureus in hospitals were already ______.

○New strains of the bacteria were resistant to penicillin within a few years. Doctors tried using another powerful antibiotic, methicillin, but again, methicillin-resistant strains of bacteria appeared.

The example of drug-resistant S. aureus highlight two important points about natural selection.

Natural selection is an ______mechanism, not a ______force. It can act only on existing variation in the population; it cannot create favorable traits, it selects for favorable traits that are already present in the population.
Natural selection favors traits that increase fitness in the ______environment. What is adaptive in one situation is not adaptive in another.

Homology

More evidence for evolution comes from similarities in the characteristics of different organisms.

Similarity in characteristic traits from ______is known as homology.

○For example, the forelimbs of ______, ______, ______, and ______share the same skeletal elements, even though the appendages have very different ______.

○These forelimbs are ______structures that represent variations on the ancestral tetrapod forelimb.

Homologies that are not obvious in adult organisms may become evident when we look at embryonic development.
Some of the most interesting homologous structures are ______structures, structures that have marginal, if any, importance to a living organism but that had important functions in the organism’s ______.

○For example, the skeletons of some snakes and of fossil whales retain vestiges of the ______and ______bones of ______ancestors.

Homologies mirror the taxonomic hierarchy of the tree of life.

Some homologies, such as the ______, are shared by all living things because they arose in the ______. Other homologies that evolved more recently are shared by only smaller branches of the tree of life.
The pattern of descent from common ancestors and the resulting homologies can be shown in an evolutionary tree, which reflects evolutionary relationships among groups of organisms.
Distantly related organisms may resemble each other because of convergent evolution, ______.
Their resemblance is ______, not homologous.
NOTE: Analogy = common function (eg bat wing, bird wing)

Homology = common ancestry (eg. wing, arm, flipper)

The fossil record

The fossil record documents the pattern of evolution, showing that past organisms differed from present-day organisms and that many species have become ______.
Over longer time scales, fossils document the origin of major groups of organisms and the evolutionary changes within these groups.

Biogeography

Evidence for evolution also comes from biogeography, ______.
The geographic distribution of organisms is influenced by many factors, including ______.

We can also use our understanding of evolution to explain biogeographic data.
For example, islands generally have endemic species ______.
Most island species are closely related to species from ______or a neighboring island, reflecting the pattern of colonization of the island.

What is theoretical about the Darwinian view of life?

Some people dismiss the Darwinian view as “______.”

○The term theory has a very different meaning in science than in everyday use.

A unifying theory does not become widely accepted unless ______.

○That has certainly been the case with the theory of evolution by natural selection.

Scientists continue to test Darwin’s theory.

Chapter 23  The Evolution of Populations

Student Guided Notes

Overview: The Smallest Unit of Evolution

Natural selectiondoes act on individuals. Each individual’s traits affect its survival and its reproductive success relative to other individuals in the population.
The evolutionary impact of natural selection is apparent only in the changes in a population of organisms over time and so it is the ______, not the ______, which evolves.
Microevolution is defined as ______.
Three mechanisms can cause allele frequencies to change: ______, ______(chance events that alter allele frequencies), and ______(the transfer of alleles between populations).

Concept 23.1 Genetic variation makes evolution possible

Genetic variation occurs within a population.

Individual variation occurs in all species and often reflects genetic variation, ______.
Both quantitative and discrete characters contribute to variation within a population.
Discrete characters, such as flower color, are usually determined by a single locus with different alleles that produce distinct phenotypes.
Quantitative characters, such as plant height, vary along a continuum within a population.

Genetic variation occurs between populations.

Species also exhibit geographic variation, differences in the genetic composition of geographically separate populations.
Geographic variation in the form of graded change in a trait along a geographic axis is called a cline (example: birds have increasing body fat as latitude increases.)

New genes and new alleles originate only by mutation.

The genetic variation on which evolution depends originates when ______, ______, or other processes produce new ______and new ______.
New alleles can arise by mutation, ______.
Some genetic variation in populations represents neutral variation that does not ______(example: fingerprints.)
The tendency for natural selection to reduce variation is countered by mechanisms that ______, including diploidy and balanced polymorphisms.
Diploidy, having two copies of each chromosome, in eukaryotes prevents the elimination of recessive alleles via selection because recessive alleles do not affect the phenotype in heterozygotes.

Even recessive alleles that are unfavorable can persist in a population by “hiding” in heterozygous individuals.

Heterozygote protection maintains a huge pool of alleles that may not be suitable under the present conditions but may become beneficial when the environment changes. (balanced polymorphism)
Sexual reproduction also increases variety via: ______, ______and ______.

Concept 23.2 The Hardy-Weinberg equation can be used to test whether a population ______

For a population to evolve, individuals must differ genetically and one of the factors that causes evolution must be at work.

A population’s gene pool is defined by its allele frequencies.

A population is ______.
The total of all the alleles for all of the loci for all of the individuals in a population is called the population’s ______.
Each allele has a frequency or proportion in the population’s gene pool.
For example, imagine a population of 500 wildflower plants with two alleles (CR and CW) at a locus that codes for flower pigment.

Suppose that in the imaginary population of 500 plants, 20 (4%) are homozygous for the CW allele (CWCW) and have ______flowers.
Of the remaining plants, 320 (64%) are homozygous for the CR allele (CRCR) and have ______flowers.
These alleles show incomplete dominance,so 160 (32%) of the plants are heterozygous (CRCW) and produce ______flowers.

Because these plants are diploid, the population of 500 plants has 1,000 copies of the gene for flower color.

The dominant allele (CR) accounts for 800 copies (320 × 2 for CRCR + 160 × 1 for CRCW)  640 + 160 = 800.
The frequency of the CR allele in the gene pool of this population is 800/1,000 = 0.8, or ______%.
The CW allele must have a frequency of 1.0 − 0.8 = 0.2, or ______%.

When there are two alleles at a locus, the convention is to use p to represent the frequency of one allele and q to represent the frequency of the other.

Thus p, the frequency of the CR allele in this population, is _____.
The frequency of the CW allele, represented by q, is ______.

Allele and genotype frequencies can be used to test whether ______is occurring in a population.

The Hardy-Weinberg principle describes a non-evolving population.

The Hardy-Weinberg principle states that the frequencies of alleles and genotypes in a population’s gene pool will remain constant over generations unless acted upon by agents other than Mendelian segregation and recombination of alleles.

The shuffling of alleles by meiosis and random fertilization has no effect on the overall gene pool of a population.
Such a gene pool is said to be in ______.

The Hardy-Weinberg principle states that the repeated shuffling of a population’s gene pool over generations does not increase the frequency of one allele over another.

Theoretically, the allele frequencies in our flower population should remain 0.8 for CR and 0.2 for CW forever.

In a population that has two alleles with frequencies p and q, the combined frequencies must add to 1, or 100%.

Therefore p + q = 1.0
____= frequency of dominant allele (B)
____ = frequency of recessive allele (b)

In addition, the genotype frequencies must add to 1.0: _____ + _____ + _____= ______.

_____= frequency of homozygous dominant (BB)
_____ = frequency of heterozygous dominant (Bb)
_____ = frequency of homozygous recessive (bb)

This general formula is the Hardy-Weinberg equation.
Using this formula, we can calculate the frequencies of alleles in a gene pool if we know the frequencies of genotypes, or we can calculate the frequencies of genotypes if we know the frequencies of alleles.
TIP: ALWAYS SOLVE FOR q FIRST!!!

Five conditions must be met for a population to remain in Hardy-Weinberg equilibrium.

Populations evolve because five conditions for non-evolving populations are rarely met for long in nature. A population must satisfy all five conditions to remain in Hardy-Weinberg equilibrium:

______. The gene pool is modified if mutations alter alleles or if entire genes are deleted or duplicated.
______. If individuals pick mates with certain genotypes, or if inbreeding is common, the mixing of gametes will not be random and genotype frequencies will change.
______. Differential survival or reproductive success among genotypes will alter allele frequencies.
______. In small populations, chance fluctuations in the gene pool will cause allele frequencies to change over time, a process called genetic drift.
______. Gene flow, the transfer of alleles due to the migration of individuals or gametes between populations, will change the frequencies of alleles.

NOTE: Hardy-Weinberg explains NON-EVOLVING populations! If one or more of these 5 conditions ARE NOT met, then that means the population is EVOLVING.

We can apply the Hardy-Weinberg principle to a human population.

We can use the Hardy-Weinberg principle to estimate the percent of the human population that carries the allele for the inherited disease ______(PKU). (refer to Genetic Disorder Chart CH 14/15)
From the epidemiologic data, we know that the frequency of homozygous recessive individuals (q2 in the Hardy-Weinberg principle) is one in ______, or 0.0001.

The frequency of the ______allele (q) is the square root of 0.0001 = 0.01.
The frequency of the ______allele (p) is p = 1 − q,or 1 − 0.01 = 0.99.
The frequency of carriers (heterozygous individuals) is 2pq = 2 × 0.99 × 0.01 = 0.0198, or about __%.

Thus, about 2% of the U.S. population carries the PKU allele.

Concept 23.3 Natural selection, genetic drift, and gene flow can alter allele frequencies in a population

Natural selection is based on differential survival and reproductive success.

Individuals with variations better suited ______tend to produce more ______than those with variations that are less well suited.
As a result of selection, alleles are passed on to the next generation in frequencies different from their relative frequencies in the present population.
For example, the fruit fly Drosophila melanogaster has an allele that confers resistance ______, including ______.

In 20 years after the first use of DDT, the allele frequency shifted from 0% to _____%.
DDT was a strong ______force, favoring alleles that conferred resistance.
Note: If DDT had eliminated ALL pests in the early application (no survivors) it would have been effective.

By ______can cause adaptive evolution(evolution that results in a better match between organisms and their environment).

Genetic drift results from chance fluctuations in allele frequencies in small populations.

______ occurs when changes in gene frequencies from one generation to another occur because of ______events (sampling errors) that occur in small populations.
Genetic drift in ______populations may occur as a result of two situations: the bottleneck effect or the founder effect.
The ______effect occurs when a new population is started by a small number of individuals who do not represent the gene pool of the larger source population.
The bottleneck effect occurs when the numbers of individuals in a large population are drastically ______by a disaster.
FOUR key points about Genetic Drift:
______.
______.
______.
______.

A population may lose or gain alleles by gene flow.