Development, Evolution and classification

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Development, Evolution and classification

• AP Biology

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From Single Cell to Multicellular Organism

• Genetic analysis and DNA technology have
  revolutionized the study of development
• Researchers use mutations to deduce developmental
  pathways
• They apply concepts and tools of molecular
  genetics to the study of developmental biology

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• Researchers select model organisms that are
  representative of a larger group, suitable for
  the questions under investigation, and easy to
  grow in the lab
• - Fruit flies, zebra fish, mice, C. elegans

Video C. elegans Crawling
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Embryonic development involves cell division,
cell differentiation, and morphogenesis

• In embryonic development of most organisms, a
  single-celled zygote gives rise to cells of many
  different types, each with a different structure
  and corresponding function
• Development involves three processes cell
  division, cell differentiation, and morphogenesis
  (creation of form)

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• Through a succession of mitotic cell divisions,
  the zygote gives rise to a large number of cells
• In cell differentiation, cells become specialized
  in structure and function
• Morphogenesis encompasses the processes that give
  shape to the organism and its various parts

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LE 21-4
Animal development
Gut
Cell movement
Zygote (fertilized egg)
Eight cells
Blastula (cross section)
Gastrula (cross section)
Adult animal (sea star)
Cell division
Morphogenesis
Observable cell differentiation
Seed leaves
Plant development
Shoot apical meristem
Root apical meristem
Two cells
Zygote (fertilized egg)
Embryo inside seed
Plant
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Different cell types result from differential
gene expression in cells with the same DNA

• Differences between cells in a multicellular
  organism come almost entirely from gene
  expression, not differences in the cells genomes
• These differences arise during development, as
  regulatory mechanisms turn genes off and on

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Evidence for Genomic Equivalence

• Many experiments support the conclusion that
  nearly all cells of an organism have genomic
  equivalence (the same genes)
• A key question that emerges is whether genes are
  irreversibly inactivated during differentiation

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Totipotency

• One experimental approach for testing genomic
  equivalence is to see whether a differentiated
  cell can generate a whole organism
• A totipotent cell is one that can generate a
  complete new organism
• Cloning is using one or more somatic cells from a
  multicellular organism to make a genetically
  identical individual

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The Stem Cells of Animals

• A stem cell is a relatively unspecialized cell
  that can reproduce itself indefinitely and
  differentiate into specialized cells of one or
  more types
• Stem cells isolated from early embryos at the
  blastocyst stage are called embryonic stem cells
• The adult body also has stem cells, which replace
  nonreproducing specialized cells
• Embryonic stem cells are totipotent, able to
  differentiate into all cell types
• Adult stem cells are pluripotent, able to give
  rise to multiple but not all cell types

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LE 21-9
Embryonic stem cells
Adult stem cells
Pluripotent cells
Totipotent cells
Cultured stem cells
Different culture conditions
Different types of differentiated cells
Liver cells
Nerve cells
Blood cells
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Transcriptional Regulation of Gene Expression
During Development

• Cell determination precedes differentiation and
  involves expression of genes for tissue-specific
  proteins
• Tissue-specific proteins enable differentiated
  cells to carry out their specific tasks

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Cytoplasmic Determinants and Cell-Cell Signals in
Cell Differentiation

• Maternal substances that influence early
  development are called cytoplasmic determinants
• These substances regulate expression of genes
  that affect the cells developmental fate

Animation Cell Signaling
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LE 21-11a
Unfertilized egg cell
Sperm
Molecules of another cytoplasmic determinant
Molecules of a cytoplasmic determinant
Nucleus
Fertilization
Zygote (fertilized egg)
Mitotic cell division
Two-celled embryo
Cytoplasmic determinants in the egg
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• The other important source of developmental
  information is the environment around the cell,
  especially signals from nearby embryonic cells
• In the process called induction, signal molecules
  from embryonic cells cause transcriptional
  changes in nearby target cells

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LE 21-11b
Early embryo (32 cells)
Signal transduction pathway
NUCLEUS
Signal receptor
Signal molecule (inducer)
Induction by nearby cells
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Pattern formation

• Pattern formation is the development of a spatial
  organization of tissues and organs
• It occurs continually in plants, but it is mostly
  limited to embryos and juveniles in animals
• Positional information, the molecular cues that
  control pattern formation, tells a cell its
  location relative to the body axes and to
  neighboring cells

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The Life Cycle of Drosophila

• Pattern formation has been extensively studied in
  the fruit fly Drosophila melanogaster
• After fertilization, positional information
  specifies the body segments in Drosophila
• Positional information triggers the formation of
  each segments characteristic structures
• Sequential gene expression produces regional
  differences in the formation of the segments

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Axis Establishment

• Maternal effect genes encode for cytoplasmic
  determinants that initially establish the axes of
  the body of Drosophila
• These maternal effect genes are also called
  egg-polarity genes because they control
  orientation of the egg and consequently the fly

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Segmentation Pattern

• Segmentation genes produce proteins that direct
  formation of segments after the embryos major
  body axes are formed
• Positional information is provided by sequential
  activation of three sets of segmentation genes
  gap genes, pair-rule genes, and segment-polarity
  genes

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Identity of Body Parts

• The anatomical identity of Drosophila segments is
  set by master regulatory genes called homeotic
  genes
• Mutations to homeotic genes produce flies with
  strange traits, such as legs growing from the
  head in place of antennae

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• Cell signaling is involved in apoptosis,
  programmed cell death
• In vertebrates, apoptosis is part of normal
  development of the nervous system, operation of
  the immune system, and morphogenesis of hands and
  feet in humans and paws in other mammals

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LE 21-19
Interdigital tissue
1 mm
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Widespread Conservation of Developmental Genes
Among Animals

• Molecular analysis of the homeotic genes in
  Drosophila has shown that they all include a
  sequence called a homeobox
• An identical or very similar nucleotide sequence
  has been discovered in the homeotic genes of both
  vertebrates and invertebrates

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LE 21-23
Adult fruit fly
Fruit fly embryo (10 hours)
Fly chromosome
Mouse chromosomes
Mouse embryo (12 days)
Adult mouse
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• Related genetic sequences have been found in
  regulatory genes of yeasts, plants, and even
  prokaryotes
• In addition to developmental genes, many other
  genes are highly conserved from species to
  species
• Sometimes small changes in regulatory sequences
  of certain genes lead to major changes in body
  form, as in crustaceans and insects

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Evolution and classification
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Gene Pools and Allele Frequencies

• A population is a localized group of individuals
  capable of interbreeding and producing fertile
  offspring
• The gene pool is the total aggregate of genes in
  a population at any one time
• The gene pool consists of all gene loci in all
  individuals of the population

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Individuals dont evolvepopulations do

• Each gene exists in two or more forms called
  alleles
• Variation in a species results from one or more
  of the following mutations, crossing over during
  meiosis 1, independent assortment of alleles,
  fertilization, changes in chromosome structure or
  number
• Only mutation creates new alleles

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Microevolution

• Change in relative allele frequency over time if
  allele frequency changes evolution occurs
• Causes of microevolution
• Genetic drift change in a small gene pool due to
  chance
• Bottleneck event population size is drastically
  reduced, leaving only the alleles of the
  survivors in the gene pool

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• Founder effect the small group starting a new
  colony contribute only their alleles to the new
  population
• Gene flow gain or loss of alleles through
  immigration or emigration
• Non-random mating organisms tend to mate with
  neighbors although they are capable of mating
  with any member of their species anywhere on earth

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Figure 23.4 Genetic drift
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LE 23-8
Original population
Bottlenecking event
Surviving population
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Hardy-Weinberg

• Their formulas are used to establish allele
  frequencies at genetic equilibrium (no evolution
  is occurring)
• The following conditions must all be fulfilled
• The population is very, very large
• There is no migration of individuals
• No mutations
• Mating is completely random
• All members survive and reproduce successfully

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The formulas

• Allele frequency fraction of that particular
  allele in the population
• The sum of all the allele frequencies 1
• p frequency of the dominant allele
• q frequency of the recessive allele
• p q 1 use for single alleles
• To figure the frequency of each genotype use p2
  2pq q2 1 use for genotypes, phenotypes or
  individuals

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Figure 23.3a The Hardy-Weinberg theorem
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Figure 23.3b The Hardy-Weinberg theorem
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Sample problem

• In mice brown coat color, B, is dominant to
  white, b. The frequency of the dominant allele is
  .6 and the frequency of the recessive allele is
  .4. What is the probability of producing each
  genotype of offspring?

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Sample problem 2

• Given the following gene pool
• R r r r r
• r r r r r
• R R r r r
• R R r r R
• What is the value of p? Of q2? Of 2pq? Of p2?

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Natural selection

• The major microevolutionary process that results
  in differential survival and reproduction
• There is variation among individuals
• More are born than can survive
• There is competition for resources
• Those individuals that are most fit for their
  environment survive, reproduce and pass on their
  alleles.

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Types of selection

• Directional selection favors individuals at one
  end of the phenotypic range
• Disruptive selection favors individuals at both
  extremes of the phenotypic range
• Stabilizing selection favors intermediate
  variants and acts against extreme phenotypes

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LE 23-12
Original population
Frequency of individuals
Original population
Evolved population
Phenotypes (fur color)
Directional selection
Disruptive selection
Stabilizing selection
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Sexual Selection

• Sexual selection is natural selection for mating
  success
• It can result in sexual dimorphism, marked
  differences between the sexes in secondary sexual
  characteristics

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• Intersexual selection occurs when individuals of
  one sex (usually females) are choosy in selecting
  their mates from individuals of the other sex
• Selection may depend on the showiness of the
  males appearance

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• Speciation, the origin of new species, is at the
  focal point of evolutionary theory which explains
  how new species originate and how populations
  evolve
• Microevolution consists of adaptations that
  evolve within a population, confined to one gene
  pool
• Macroevolution refers to evolutionary change
  above the species level

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Limitations of the Biological Species Concept

• The biological species concept does not apply to
• Asexual organisms
• Fossils
• Organisms about which little is known regarding
  their reproduction

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Isolating mechanisms

• Prezygotic barriers prevent mating or
  fertilization
• Habitat isolation live in the same place but
  never meet
• Temporal isolation reproduce at different times
• Behavioral isolation mating rituals
• Mechanical isolation parts have to fit to
  deliver the gametes
• Gametic isolation species specific proteins and
  receptor sites

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• Postzygotic barriers prevent the hybrid zygote
  from developing into fertile adults
• Reduced hybrid viability-meet, mate, no offspring
  produced
• Reduced hybrid fertility-meet, mate, offspring
  are sterile
• Hybrid breakdown-meet, mate offspring mate but
  their offspring die

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Figure 24.3 Courtship ritual as a behavioral
barrier between species
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Allopatric speciation

• In allopatric speciation, a physical barrier cuts
  off the gene flow between 2 or more populations
• If conditions are different in areas of the 2
  populations, they can become reproductively
  incompatible and cannot interbreed, making them
  into 2 different species

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Sympatric speciation

• In sympatric speciation species arise from within
  the range of existing species, in the absence of
  physical or ecological barriers
• Paripatric speciation occurs at borders of
  populations

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Figure 24.6 Two modes of speciation
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LE 24-6
A. leucurus
A. harrisi
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Figure 24.8 Has speciation occurred during
geographic isolation?
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Tempo of speciation

• Gradulism tree diagrams have branches at slight
  angles showing slow steady change over time
• Punctuated equilibrium tree has short,
  horizontal branches that show rapid periods of
  change followed by stable periods

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Figure 24.17 Two models for the tempo of
speciation
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• Two basic patterns of evolutionary change
• Anagenesis (phyletic evolution) transforms one
  species into another
• Cladogenesis (branching evolution) is the
  splitting of a gene pool, giving rise to one or
  more new species

Animation Macroevolution
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LE 24-2
Anagenesis
Cladogenesis
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Adaptive radiation

• Burst of microevolutionary activity that result
  in the formation of new species in a wide range
  of habitats
• A small group of founders start a new colony if
  there are available niches and enough variation
  in the genes of the population they can evolve
  into many different species over time (finches)

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Figure 24.11 A model for adaptive radiation on
island chains
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Evidence for evolution

• Fossil record and biogeography
• Similar fossils in South America and Africa
• Comparative morphology
• Homologous structures
• Analogous structures
• Embryological development
• vertebrates
• Biochemical comparisons
• Proteins
• Nucleic acids

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The 6 kingdoms

• Monera now are 2 kingdoms eubacteria and
  archaebacteria
• Protista
• Fungi
• Plantae
• Animalia

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Taxonomy

• Taxonomy is the ordered division of organisms
  into categories based on characteristics used to
  assess similarities and differences
• In 1748, Carolus Linnaeus published a system of
  taxonomy based on resemblances.
• Two key features of his system remain useful
  today two-part names for species and
  hierarchical classification

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Binomial Nomenclature

• The two-part scientific name of a species is
  called a binomial
• The first part of the name is the genus
• The second part, called the specific epithet, is
  unique for each species within the genus
• The first letter of the genus is capitalized, and
  the entire species name is latinized
• Both parts together name the species (not the
  specific epithet alone)

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Hierarchical Classification

• Linnaeus introduced a system for grouping species
  in increasingly broad categories
• Domain, Kingdom, Phylum, Class, Order, Family,
  Genus, Species

Animation Classification Schemes
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LE 25-8
Panthera pardus
Species
Panthera
Genus
Felidae
Family
Carnivora
Order
Mammalia
Class
Chordata
Phylum
Animalia
Kingdom
Eukarya
Domain
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Linking Classification and Phylogeny

• Systematists depict evolutionary relationships in
  branching phylogenetic trees
• Each branch point represents the divergence of
  two species
• Deeper branch points represent progressively
  greater amounts of divergence

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LE 25-9
Panthera pardus (leopard)
Mephitis mephitis (striped skunk)
Lutra lutra (European otter)
Canis familiaris (domestic dog)
Canis lupus (wolf)
Species
Genus
Panthera
Mephitis
Lutra
Canis
Family
Felidae
Mustelidae
Canidae
Carnivora
Order
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Figure 25.12 Cladistics and taxonomy
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LE 22-15
Pharyngeal pouches
Post-anal tail
Chick embryo (LM)
Human embryo
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LE 22-16
Percent of Amino Acids That Are Identical to the
Amino Acids in a Human Hemoglobin Polypeptide
Species
Human
100
95
Rhesus monkey
87
Mouse
69
Chicken
54
Frog
14
Lamprey
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LE 25-UN497
Leopard
Domestic cat
Common ancestor
Leopard
Domestic cat
Wolf
Common ancestor
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Phylogenetic trees are made based on shared
characteristics

• A cladogram depicts patterns of shared
  characteristics among taxa
• A clade is a group of species that includes an
  ancestral species and all its descendants
• Cladistics studies resemblances among clades

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Cladistics

• Clades can be nested in larger clades, but not
  all groupings or organisms qualify as clades
• A valid clade is monophyletic, signifying that it
  consists of the ancestor species and all its
  descendants
• A paraphyletic grouping consists of an ancestral
  species and some, but not all, of the descendants
• A polyphyletic grouping consists of various
  species that lack a common ancestor

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LE 25-10a
Grouping 1
Monophyletic
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LE 25-10b
Grouping 2
Paraphyletic
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LE 25-10c
Grouping 3
Polyphyletic
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Shared Primitive and Shared Derived
Characteristics

• In cladistic analysis, clades are defined by
  their evolutionary novelties
• A shared primitive character is a character that
  is shared beyond the taxon we are trying to
  define
• A shared derived character is an evolutionary
  novelty unique to a particular clade

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Outgroups

• An outgroup is a species or group of species that
  is closely related to the ingroup, the various
  species being studied
• We compare each ingroup species with the outgroup
  to differentiate between shared derived and
  shared primitive characteristics

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• The outgroup and ingroup share primitive
  characters that predate the divergence of both
  groups from a common ancestor
• The focus is on characters derived at various
  branch points in the evolution of a clade

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LE 25-11
TAXA
Lancelet (outgroup)
Salamander
Lamprey
Leopard
Turtle
Tuna
Hair
Amniotic (shelled) egg
Four walking legs
CHARACTERS
Hinged jaws
Vertebral column (backbone)
Character table
Leopard
Turtle
Hair
Salamander
Amniotic egg
Tuna
Four walking legs
Lamprey
Hinged jaws
Lancelet (outgroup)
Vertebral column
Cladogram
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Trait Shark Frog Kangaroo human
Vertebrae X X X X
2 pairs of limbs X X X
Mammary glands X X
Placenta X
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