Transcript document

Chapter 2
Biology and Evolution
Chapter Outline
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Evolution and Creation Stories
The Classification of Living Things
The Discovery of Evolution
Heredity
Evolution, Individuals, and Populations
Adaptation and Physical Variation
Great Chain of Being
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An early form of classification of living things used in
Europe.
Developed by Aristotle in ancient Greece over 2,000
years ago.
Categories were based upon visible similarities with a
member of each category considered a “primate”.
– The primate of rocks was the diamond.
– Humans were at the very top of the ladder, just
below the angels.
Systema Naturae
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Classificatory system developed by Carolus Linnaeus
in the 18th century to classify all living things.
Linnaeus classified living things into categories that
are progressively more inclusive on the basis of
internal and external visual similarities.
Species are the smallest working units in biological
classificatory systems.
Species are subdivisions of larger, more inclusive
groups, called genera.
Criteria of Linnaeus Classificatory
System
1.
2.
3.
Body structure: A Guernsey cow and a Holstein cow
are the same species because they have identical
body structure.
Body function: Cows and horses give birth to live
young. Although they are different species, they are
closer than either cows or horses are to chickens.
Sequence of bodily growth: At the time of birth—or
hatching out of the egg—young cows and chickens
resemble their parents in their body plan.
Taxonomy
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The science of classification.
 It is based on more than body structure,
function, and growth; today scientists base
taxonomy also on molecular comparisons.
Analogies
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In biology, structures possessed by different
organisms that are superficially similar due to
similar function; without sharing a common
developmental pathway or structure.
Homologies
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In biology, structures possessed by two
different organisms that arise in similar
fashion and pass through similar stages
during embryonic development though they
may possess different functions.
Classification of Humans
Taxonomic
Category
Kingdom
Category to Which Humans Belong
Animalia
Phylum
Chordata
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Subphylum
Vertebrata
Class
Mammalia
Order
Primates
Classification of Humans
Taxonomic Category
Human Category
Suborder
Anthropoidea
Superfamily
Hominoid
Subphylum
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Family½ TABLE 2.1 P. 31
Vertebrata
Subfamily
Hominid
Hominin
Genus
Species
Homo
sapiens
Theory of Natural Selection
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Charles Darwin formulated the theory of natural
selection and published it in 1859.
Darwin combined his observations into the theory of
natural selection as follows:
– All species display variation and have the ability to
expand beyond their means of subsistence.
– In their “struggle for existence,” organisms with
variations that help them survive will reproduce
more successfully.
– Nature selects the most advantageous variations,
and species evolve.
The Transmission of Genes
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A gene is a portion of the DNA molecule that
contains a sequence of base pairs that
encode a particular protein.
 Mendel deduced the presence and activity of
genes by experimenting with garden peas to
determine how traits are passed from one
generation to the next.
 He discovered that inheritance was
particulate, rather than blending, as Darwin
thought.
The Law of Segregation
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Units controlling the expression of visible
traits come in pairs, one from each parent,
and retain their separate identities over the
generations rather than blending into a
combination of parental traits in offspring.
The Law of Independent
Assortment
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The Mendelian principle that genes
controlling different traits are inherited
independently of one another.
Chromosones
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In the cell nucleus, chromosones are the
structures visible during cellular division
containing long strands of DNA combined
with a protein.
 When chromosomes were discovered at the
start of the 20th century, they provided a
visible vehicle for transmission of traits
proposed in Mendel’s laws.
DNA
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Deoxyribonucleic acid.
 The genetic material consisting of a complex
molecule whose base structure directs the
synthesis of proteins.
 In 1953 James Watson and Francis Crick
found that genes are actually portions of
molecules of DNA.
DNA Structure
INSERT FIGURE 2.1 P. 34
Alleles
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Alternate forms of a single gene.
 Example:
– The gene for a human blood type in the AB-O system refers to a specific portion of a
DNA molecule, and alleles correspond to
alternate forms of this gene that determine
the specific blood type (A allele, B allele, C
allele).
Humane Genome
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The complete sequence of human DNA.
 The genome contains 3 billion chemical
bases, with about 20,000–25,000 functioning
genes, a number similar to that found in most
mammals.
 Of the 3 billion bases, humans and mice are
about 90 percent identical.
Cell Division
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In order to grow and maintain good health,
the body cells of an organism must divide and
produce new cells.
 Cell division is initiated when chromosomes
replicate, forming a second pair that
duplicates the original pair of chromosomes
in the nucleus.
Mitosis
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A kind of cell division that produces new cells having
exactly the same number of chromosome pairs as
the parent cell.
 The DNA “unzips” between the base pairs—adenine
from thymine and guanine from cytosine.
 Each base on each now-single strand attracts its
complementary base, reconstituting the second half
of the double helix.
 Each new pair is surrounded by a membrane and
becomes the nucleus of a new cell.
 As long as no errors are made in the process, cells
within organisms can divide to form daughter cells
that are exact genetic copies of the parent cell.
Meiosis (Sexual Reproduction)
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A kind of cell division that produces sex cells, each of
which has half the number of chromosomes found in
other cells of the organism.
In humans this involves 23 pair of chromosomes.
Sexual reproduction increases genetic diversity and
has contributed to adaptations among sexually
reproducing species.
Meiosis
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Meiosis is cell division that produces sex
cells, each of which has half the number of
chromosomes found in other cells.
 If two regular body cells, each containing 23
pairs of chromosomes, merged, the result
would be an individual with 46 pairs of
chromosomes; they could not survive.
 This doesn’t occur because sex cells that join
to form a new individual are the product of
meiosis.
Mitosis and Meiosis
INSERT FIGURE 2.2 P. 37
The Punnett Square
INSERT FIGURE 2.3 P. 37
Genotype
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The alleles possessed for a particular trait.
Heterozygous
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Refers to a chromosome pair that bears
different alleles for a single gene.
Homozygous
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Refers to a chromosome pair that bears
identical alleles for a single gene.
Dominance
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The ability of one allele for a trait to mask the
presence of another allele.
Recessive
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An allele for a trait whose expression is
masked by the presence of a dominant allele.
Dominance and Recessiveness
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Recessive alleles can be handed down for
generations before they are matched with
another recessive allele in the process of
sexual reproduction and show up in the
phenotype.
 The presence of the dominant allele masks
the expression of the recessive allele.
Phenotype
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The observable or testable appearance of an
organism that may or may not reflect a
particular genotype due to the variable
expression of dominant and recessive alleles.
Hemoglobin
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The protein that carries oxygen in the red
blood cells.
Polygenetic Inheritance
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When two or more genes contribute to the
phenotypic expression of a single character.
Evolution, Individuals and
Populations
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In biology, a population is a group of similar
individuals that can and do interbreed.
The gene pool refers to the genetic variants
possessed by all members of a population.
Natural selection also takes place within populations.
Over generations, the relative proportions of alleles in
a population changes according to the reproductive
success of individuals within that population. This is
called microevolution.
Microevolution
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At the level of population genetics, evolution is
defined as changes in allele frequencies in
populations, or microevolution.
Four evolutionary forces—mutation, gene flow,
genetic drift, and natural selection—are responsible
for the genetic changes that underlie biological
variation.
These evolutionary forces create and pattern
diversity.
Mutation
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Mutation is the ultimate source of
evolutionary change that constantly
introduces new variation.
 For sexually reproducing species like
humans, only mutations that occur in sex
cells are of any evolutionary consequence.
 Mutations may arise whenever copying
mistakes are made during cell division.
Some Causes of Mutation
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Environmental factors such as dyes, antibiotics, and
chemicals may increase the rate at which mutations
occur.
Radiation (industrial or solar) is also a cause of
mutations.
Stress can increase mutation rates, increasing the
diversity necessary for selection if successful
adaptation is to occur.
Mutation Process
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In all multicellular animals, genetic material
ensures that mutations will occur.
 Genes are split by stretches of DNA that are
not a part of that gene, increasing the
chances that a simple mistake in the process
of copying DNA will cause mutations.
 Mutations occur randomly and do not arise
out of need for some new adaptation.
Genetic Drift
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Refers to chance fluctuations of allele
frequencies of the gene pool of a population.
 These changes are a result of random events
at the individual level.
 Genetic drift is likely to have been an
important factor in human evolution, because
until 10,000 years ago, all humans were food
foragers who lived in small, self-contained
populations.
Founder Effects
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A particular kind of genetic drift that may
occur when an existing population splits up
into two or more new ones, especially if one
of the new populations is founded by a
particularly small number of individuals.
 It is unlikely that the gene frequencies of the
smaller population will be representative of
those of the larger one.
Gene Flow
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The introduction of new alleles from nearby
populations.
 Interbreeding allows genes to flow in and out
of populations, increasing variation within a
population.
 Migration and geographical factors lead to
gene flow.
 Among humans, social factors such as
mating rules, intergroup conflict, and our
ability to travel great distances affect gene
flow.
Natural Selection
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The evolutionary process through which
genetic variation at the population level is
shaped to fit local environmental conditions.
 Over time, changes in the genetic structure of
the population are visible in the biology or
behavior of a population, and such genetic
changes can result in the formation of new
species.
Sickle-Cell Trait
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The sickle-cell trait, caused by the inheritance
of an abnormal form of hemoglobin, is an
adaptation found in regions in which malaria
is common.
 In these regions, the sickle-cell trait plays a
beneficial role.
 In other parts of the world, the sickling trait is
not advantageous and sickle- cell anemia is
harmful.
Sickle-Cell Anemia
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A disease in which the oxygen-carrying red
blood cells change shape and clog the
circulatory system.
 Geneticists predict that as malaria is brought
under control, within several generations,
there will be a decline in the number of
individuals who carry the allele responsible
for sickle-cell anemia.
Sickle-cell Anemia
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Adaptation and Physical
Variation
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Anthropologists study biological diversity in
terms of clines, or the continuous gradation
over space in the form or frequency of a trait.
 Clinal analysis of a continuous trait, such as
body shape, allows anthropologists to
interpret human variation in body build as an
adaptation to climate.
 People native to cold climates tend to have
greater body bulk relative to their arms and
legs than people native to hot climates.