Download Unit 6

Macias, Rachel
1/25/03
Period 3
Chapter 22: A Darwinian View of Life
OBJECTIVES
After reading this chapter and attending lecture, the student should be able to:
1. State the two major points Darwin made in The Origin of Species concerning the Earth's biota.
1) He argues from evidence that species were not specially created in their present forms but had evolved
from ancestral species.
2) He proposed a mechanism for evolution, natural selection.
2. Describe Carolus Linnaeus' contribution to Darwin's theory of evolution.
He sought order in life’s diversity. He founded taxonomy, the branch of biology concerned with naming
and classifying the diverse forms of life by species, genus, family, etc. Although created to support
creationism, the system later became the focal point of Darwin’s argument for evolution.
3. Describe Jean Baptiste Lamarck's model for how adaptations evolve.
Lamarck saw through fossils a series of older to younger fossils leading to a modern species. At the bottom
were microorganisms which he believed continually generated spontaneously from inanimate material. At
the top are the most complex plants and animals. He believed evolution responded to “felt” need of a
species, pushing its evolution on to perfection. He also believed in disuse, the idea that parts of the body
used extensively to cope with the environment become larger/stronger and those that are not used
deteriorate. Additionally he believed that when modifications to a character trait occurs in an organism, they
are passed on to the next generation.
4. Explain what evidence convinced Darwin that species change over time.
At 22 he traveled the South American Coast on the Beagle and studied its life forms. He noticed all
resembled each other and similarities were unique only to South America. In the Galapagos Islands he
collected 13 types of finches that seemed to be of different species although they were very similar.
5. Explain why variation was so important to Darwin's theory.
Variation was important because Darwin’s whole theory was that species had developed from one specie that
fragmented into several local populations isolated by the geography around them. That population would
change more and more in appearance to adapt to local conditions. He predicted that over time they’d be
different enough to become species.
6. Define and state the basic principles in natural selection.
Natural selection – a differential success in reproduction and its products is adaptation of organisms to their
environment. Based on his observations, Darwin inferred that: 1) overcrowding in an environment leads to
competition with only a fraction of offspring surviving, 2) survival in the struggle for existence is not
random, but depends on which species is best suited to live in their environment, and 3) over generations,
because of the unequal ability of individuals to survive and reproduce, more favorable characteristics would
be passed on and come to define the population.
7. Using some contemporary examples, explain how natural selection results in evolutionary change.
Example 1 – Two scientists at Princeton have been studying finches for 20 years and discovered that their
beak depth changes as the seasons do. Natural selection did not create adapted beaks, it just adapted what
was already there.
Example 2 – From one generation to the next of the female checkerspot butterfly, eggs were laid first on one
type of plant and then on another by the daughter generation. The reproductive behavior of the generations
was changing.
8. Describe how molecular biology can be used to study the evolutionary relationships among organisms.
Evolutionary relationships are reflected in DNA and proteins. If two species of DNA are similar, they must
have has a common ancestor. A common genetic code is evidence that all is related, as the genetic code was
passed down through all branches of evolution since its inception.
9. Explain the problem with the statement that Darwinism is "just a theory".
1) It fails to separate Darwin’s claims: modern species evolved from ancestors and natural selection is the
main mechanism for this evolution.
2) The term theory has a different meaning in science than in regular use (means hypothesis). It accounts
for many fact and attempts to explain a great variety of phenomena. It does not become accepted unless its
predictions stand up to thorough/continuous testing by experiments and observation.
Chapter 23: The Evolution of Populations
OBJECTIVES
After reading this chapter and attending lecture, the student should be able to:
1. Explain what is meant by the "modern synthesis".
Modern synthesis – it integrated discoveries and ideas from many fields of science. It is a comprehensive
theory of evolution. It emphasizes the importance of population as units of evolution, and the idea of
gradualism to explain how large changes can occur over long periods of time.
2. Explain how microevolutionary change can affect a gene pool.
Microevolution is evolution at the smallest level. If a population’s gene pool is doing such evolving, allele
and genotype frequencies at some loci may be at equilibrium while other allele frequencies may be changing.
3. In their own words, state the Hardy-Weinberg theorem.
States that allele and genotype frequencies in a population’s gene pool remain constant over the generations
unless acted upon by agents other than sexual recombination. In other words, sexual recombination would
have no affect on the overall genetic structure of a population.
4. Describe the usefulness of the Hardy-Weinberg model to population geneticists.
The model provides a theorem describing a nonevolving population. The allele and genotype frequencies
calculated from it provide a baseline for tracking the genetic structure of a population over a succession of
generations. If frequencies vary, the population is evolving.
5. Explain how genetic drift, gene flow, mutation, nonrandom mating and natural selection can cause
microevolution.
Genetic drift – changes in the gene pool of a population entirely due to chance; results in evolution.
Gene flow – tends to reduce the difference between populations that have accumulated by natural selection
or genetic drift. (Exchange due to migration of gametes or individuals in a population).
Mutation – substitutes one allele for another in a gene pool. It is the original source of genetic variation
that serves as raw material for natural selection.
Nonrandom mating – as a population continues to mate within itself, heterozygotes tend to diminish,
replaced instead by homozygotes.
Natural selection – differential success in reproduction. It accumulates and maintains favorable genotypes in
a population so it can survive. These genotypes however, can result only within what genetic viability
already exists in the population.
6. Distinguish between the bottleneck effect and the founder effect.
Bottleneck – disasters kill individuals of a population randomly, so the individuals left don’t usually
represent the original population’s genetic make-up. Genetic variation is not as great because at least some
of the alleles for the loci are gone.
Founder – a small population of a larger one moves to a small environment such as an island. Genetic
variation won’t be that great until the population grows to a size where genetic error is possible.
7. Explain why mutation has little quantitative effect on a large population.
Mutation does not have much quantitative effect on a population by itself in a single generation because
mutation in itself at any gene locus is very rare. The gene pool would be even less affected if the mutation
were reversible, as most are.
8. Give the cause of nearly all genetic variation in a population.
Nearly all genetic variation in a population occurs as a result of the unique recombinations of existing alleles
that each individual draws from a gene pool.
9. Explain how genetic variation may be preserved in a natural population.
Because most eukaryotes are diploid some genetic variation is hidden in the form of recessive alleles in
heterozygotes. A heterozygote gene pool maintains alleles that may not be favorable at the present, but may
later become favorable in a different environment. Selection may also preserve variation at a gene loci
(balanced polymorphism). If a heterozygote individual is more successful than a homozygote, two or more
heterozygous alleles will be maintained at that locus.
10. Describe what selection acts on and what factors contribute to the overall fitness of a genotype.
Selection acts on phenotypes; it indirectly adapts a population to its environment by increasing/maintaining
favorable genotypes in a gene pool. Overall fitness depends on whether its positive effects outweigh
harmful effects it could have on the organism’s survival or reproductive abilities. It’s effects depend on the
entire genetic context in which it works. (Ex. A tree must have alleles that make not only its trunk grow,
but also its roots in order for it to survive).
11. Give examples of how an organism's phenotype may be influenced by the environment.
Natural selection chooses not only genotypic variation, but also that which it affects, the phenotypic
variation. There are three types of this selection, stabilizing, directional, and diversifying.
12. Distinguish among stabilizing selection, directional selection and diversifying selection.
Stabilizing selection – acts against extreme phenotypes and favors the more common intermediate variants.
Reduces variation; keeps status quo for a particular phenotypic character.
Directional selection – most common during environmental change or movement of individuals to a new
habitat. Shifts frequency curve in phenotypic character by favoring the rare traits of individuals that deviate
from the average character.
Diversifying selection – when environmental conditions favor extreme phenotypic traits over intermediate
ones. Can result in balanced polymorphism.
13. Give at least four reasons why natural selection cannot breed perfect organisms.
1) Organisms are locked into historical constraints. Evolution doesn’t do away with original life form traits,
so today’s existing life still reflects the structures of past life forms.
2) Adaptations are often compromises. Example: We have arms and legs which are very useful to us, but
they are also potentially painful because we can get broken bones, torn ligaments, or sprains.
3) Not all evolution is adaptive. Not all organisms placed in a new environment are necessarily suited to
that environment.
4) Selection can only edit variations that exist. Natural selection favors the most fit variations of traits that
already exist. New alleles aren’t just created on demand.
Chapter 24: The Origin of Species
OBJECTIVES
After reading this chapter and attending lecture, the student should be able to:
1. Define biological species (E. Mayr).
Defines a species as a population of group of populations whose members have the potential to interbreed
with one another in nature to produce fertile offspring. Also, it can’t successfully interbreed with another
species.
2. Describe some limitations of the biological species concept.
The concept is useless for asexually breeding organisms. It is also inadequate for grouping already extinct
forms of life. Also, two populations could be very closely related and live nearby, but be geographically
separated so it is not certain of whether or not they could interbreed.
3. Distinguish between prezygotic and postzygotic isolating mechanisms.
Prezygotic – barriers that impede mating between species or hinder the fertilization of ova if members of
different species attempt to mate.
Postzygotic – barriers that prevent the hybrid zygote from developing into a viable, fertile adult.
4. Describe five prezygotic isolating mechanisms and give an example of each.
Habitat isolation – two species may live nearby but almost never run across each other even though they are
not technically geographically separated.
Exmaple – 2 species of garter snakes live in the same area, but one is primarily terrestrial and the other is
aquatic.
Temporal isolation – two species that breed during different times of the day, different seasons or years,
cannot mix their gametes.
Example – The geographical ranges of the western spotted and eastern spotted skunks overlap, but they
don’t interbreed because they have different breeding seasons.
Mechanical isolation – similar species attempt to mate but cannot because they are automatically
incompatible.
Example – This contributes to reproductive isolation of flowering plants pollinated by insects or other
animals.
Genetic isolation – two individuals from different species meet, but fail to form a zygote. With internal
fertilization, the sperm of one species may not be able to survive in the reproductive tract of another. With
external fertilization, cross fertilization is uncommon.
5. Explain, in their own words, how hybrid breakdown maintains separate species even if gene flow occurs.
Even if two species were to mate successfully and produce viable offspring, when that offspring next tried to
mate it would produce offspring that were feeble or sterile.
6. Distinguish between allopatric and sympatric speciation.
Allopatric – an initial block to gene flow created by a geographic barrier.
Sympatric – when a subpopulation becomes isolated within its own parent population. They must have
their ranges overlap.
7. Describe the adaptive radiation model and use it to describe how it might be possible to have many
sympatric closely related species even if geographic isolation is necessary for them to evolve.
1) An island in a cluster is seeded by species A from a nearby coastline.
2) Its gene pool is isolated from its parents on the mainland, it evolves into species B to adapt to its
surroundings.
3) Storms, etc. disperse B to a second island.
4) They are isolated and form species C.
5) Later species C cohabits with species B from the first island, but reproductive barriers keep them
separate.
6) A colony of C populates a third island.
7) Species C adapts and forms species D.
8) Species D is dispersed to two ancestral islands.
9) On those islands species E is formed.
The islands are separated geographically but still close enough to each other and the mainland to
occasionally interbreed. Also, they are so close to the mainland, there is not time to develop reproductive
barriers against the steady stream of immigrants from the parent population.
8. Define sympatric speciation and explain how polyploidy can cause reproductive isolation.
(*See # 6b). If polyploidy occurred, an individual within a population otherwise the same as itself could
become isolated reproductively.
9. List some points of agreement and disagreement between the two schools of thought about the tempo of
speciation (gradualism vs. punctuated equilibrium).
Agreement:
Disagreement:
That a rapid or sudden development of a species
Punctuationists believe that a
could take up to thousands of years.
species can remain static, not
changing once it has adapted to
its surroundings and then
natural
selection takes over.
Gradualists say stasis is an
illusion, that species must
continue to change after they
came into existence, but in such
ways that it is not detectable in
the fossil record.
Chapter 26: Early Earth and the Origin of Life
OBJECTIVES
After reading this chapter and attending lecture, the student should be able to:
1. Provide at least two lines of evidence for the antiquity of life.
1) Prokaryotes about the size of bacteria have been discovered in South Africa in a rock formation, the Fig
Tree Chart which is 34 billion years old.
2) Fossils resembling spherical and filamentous prokaryotes have been found in stromatolites (domes of
banded sediment 3.5 billion years old) in West and South Africa.
2. Describe the contributions that A.I. Oparin, J.B.S. Haldane, Stanley Miller and Harold Urey made towards
developing a model for abiotic synthesis of organic molecules.
Oparin and Haldane hypothesized that in the beginning, living/organic matter was created from nonliving
matter. They figured t doesn’t happen today because there is 02 in the air, not conducive to spontaneous
synthesis. They envisioned a primitive earth free of 02 and synthesis powered by UV radiation. Miller and
Urey tested this theory by creating a model with conditions comparable to those of an early earth. The
result was the creation of amino acids and other organic compounds found in living organisms.
3. Provide evidence to support the hypothesis that chemical evolution resulting in life's origin occurred in 4
stages:
a. Abiotic synthesis of organic monomers
Because of Miller and Urey’s experiment, it was proven that the amino acids needed to begin life and some
bases of DNA and RNA could be formed in the primordial soup.
b. Abiotic synthesis of polymers
In some lab experiments, polymerization has occurred by dripping diluted solutions of organic molecules
onto hot rocks. Waves or rain could’ve diluted these, splashing them onto fresh lava or hot rocks.
c. Formation of protobionts
These could have preceded living cells. Lab experiments show that they can form spontaneously. When
cool water is added, they become miproteinoids which swell of shrink in a salt water solution like cells do.
d. Origin of genetic information
IN a lab, if RNA is transferred to a test tube solution containing monomers to make more RNA, nucleotides
of 5-10 base pairs can be formed.
4. Describe the basis for Whittaker's five-kingdom system.
The five kingdom system (Monera, Protista, Plantae, Fungi, Animalia) recognizes two different types of cells,
prokaryotes and eukaryotes. Prokaryotes are bacteria. In the other four kingdoms, all consist of cells
organized on a eukaryotic plan. Each is defined by characteristics of structure and the life cycle. Protista is
a conglomeration of everything that didn’t fit into Plantae, Fungi, or Animalia.
5. Describe three alternatives to the five-kingdom system and explain the rationale for each.
1) 6-kingdom alternative divides prokaryotes into two kingdoms. This modification is based on molecular
evidence for a divergence between eubacteria (most bacteria) and archaebacteria, an ancient lineage of
prokaryotes with unique characteristics.
2) 3-domain alternative divides eubacteria, archaebacteria, and eukaryotes into 3 domains (one level above a
kingdom).
3) 8-kingdom alternative system solves the problem of the different lineages of microorganisms. There are
two separate prokaryotes kingdoms and protists in the three kingdoms. This system has reopened issues of
biological diversity at the highest taxonomic levels.