Transcript Diversity of Life

Diversity of Life
Biology 103
Instructor: Jim Driver
Class Information Card
Please take a few minutes to fill out a 3x5 card with the following
information:
• Name
• Major
• Class (Soph., Jr., etc)
• Related courses taken
• Career goals?
• Expectations of this course
• E-Mail address (optional)
Course Business





Instructor: Jim Driver ([email protected])
Required text: Biology, Campbell and Reese, 7th edition
Diversity of Life is a continuation of Principles of
Biology
A comprehensive syllabus and lecture schedule will be
provided
This course will have four exams, one will be a takehome
Course Business



Classroom attendance is STRONGLY
recommended
Taking clear, concise lectures notes will help in
this and future university classes
Exam questions will come from the lecture
notes. Use the textbook to better understand the
materials covered in lecture, BUT……a
thorough reading of the text will help in the
future and may be enjoyable!
How to study for my exams
• Come to class
• Take notes, pay attention to emphasis on
topics or concepts
• Use textbook to better understand notes
• Know all terms in notes
• If you have questions - ask during class or
come see me during office hours
Yes, life sure is diverse!
Diversity of Life – Course Preview


Biology of Life covered molecular biology, cell
biology, and genetics. This course covers the
rest!
But seriously, topics we will cover include:




How did life develop such diversity from its initial
beginnings?
How is life categorized?
What are the hallmarks of the major life groupings?
How does life interact on a local, regional, and
planetary level?
The molecular structure of DNA
• Holds all the information to make a complex
organism in 4 bases!
Nucleus
DNA
Cell
Nucleotide
Figure 1.7
(a) DNA double helix. This model shows
each atom in a segment of DNA.Made
up of two long chains of building
blocks called nucleotides, a DNA
molecule takes the three-dimensional
form of a double helix.
A
C
T
A
T
A
C
C
G
T
A
G
T
A
(b) Single strand of DNA. These geometric shapes and
letters are simple symbols for the nucleotides in a
small section of one chain of a DNA molecule.
Genetic information is encoded in specific sequences
of the four types of nucleotides (their names are
abbreviated here as A, T, C, and G).
Diversity and Relationships
• Carolus Linnaeus – taxonomy
– How can we put all the organisms in the right
boxes?
– Developed binomial nomenclature (Genus
species)
– He classified similar species (by morphology)
into increasingly general categories
What is common thread
in each grouping?
Evolution and Diversity
• Evolution accounts for life’s unity and
diversity
Darwin and “descent with modification”
• Lamark’s theory of evolution
– Use and disuse
– Inheritance of acquired characteristics
– Based on improvement of the individual
during its life and transmission of the
improvements to offspring
What Lamarck thought…
Darwinian Evolution
• 1859 – On The Origin of Species By
Means of Natural Selection (Alfred Russel
Wallace also had same idea)
– 2 main ideas
• Evolution explains life’s unity and diversity
• Natural selection is a cause of adaptive evolution
• Remember:
– Individuals survive and reproduce
– Populations evolve and adapt
Variation driven by random mutation and sexual recombination
Overproduction
Reproductive success
Imagine an
alternative
scenario
How did Darwin get to natural selection?
Observations and inferences.
•
•
•
•
•
•
•
•
Obs. #1 – all species have great potential fertility
#2 – populations tend to remain stable
#3 – resources are limited
Inference #1 – overproduction leads to struggle for
existence
Obs. #4 – in a population, no two individuals are alike
#5 variation is heritable
Inf. #2 – individuals with inherited traits that best fit the
environment will likely leave more offspring
Inf. #3 – unequal survival and reproduction will lead to
gradual change in a population, with favorable
characteristics accumulating over the generations
In other words….
• Natural selection is:
– differential success in reproduction
– an interaction between the environment and
the variability in individuals making up the
population
• Natural selection leads to the adaptation of
a population of organisms to their
environment
Evidence for natural selection
• Antibiotic resistance in bacteria
– Bacterial populations are not always clonal
– Mutations in DNA during replication can lead to
protein structure changes
• Moth coloration in England
– Pollution caused change in tree bark color
– Some moths stood out leading to differential
predation, changing population
• Pesticide resistance in insect populations
• Toxins in Newts
Figure 22.12
The fittest survive
and reproduce
Understand:
• Fitness –any heritable trait that increases
relative reproductive success
– Strictly dependent on the specific environment
• Adaptation – refers to populations
adapting to the environment, not the
individual
• Scientific Theory – useful, comprehensive,
and well-supported explanation for a wide
range of observations
Understand:
• Fitness –any heritable trait that increases
relative reproductive success
– Strictly dependent on the specific environment
• Adaptation – refers to populations adapting to
the environment, not the individual
• Scientific Theory – useful, comprehensive, and
well-supported explanation for a wide range of
observations
• Evolution in its strict meaning is a change in
allele frequencies in a population over
time…….But……
Time and scale of change in a population
Evolution – change through time
Macroevolution
Speciation
Microevolution
Definitions
• Microevolution – change in allele
frequencies in population over time
– Alleles - alternative versions of a gene that
produce distinguishable phenotypic effects
• Speciation – a population’s genetic
divergence leads to reproductive isolation
• Macroevolution – the level of change of life
on the planet observed over geological
time
Understanding Evolution
• Evidence indicates that all life on this
planet is related. Eg. DNA-based
• Later forms show a relationship to earlier
forms based on common characteristics
• Natural selection provides a mechanism to
explain how these changes came about
• Natural selection requires heritable
variation in populations and conditions that
favor one variant over another
Evidence for evolution
• Descent with modification can explain
similarities in structures with different
functions (homology)
• Anatomical homologies
Evidence of evolution
• Descent with modification can explain
similarities in structures with different
functions (homology)
• Anatomical homologies
• Molecular homologies
Biogeography
• The geographic distribution of species
• Closely related species inhabit same
geographic region (common evolution)
• But:
– Same ecological niches in distant regions can
be occupied by evolutionarily different species
Biogeography
• The geographic distribution of species
• Closely related species inhabit the same
geographic region
• But: these ecological niches in distant regions
can be occupied by evolutionarily different
species
• Darwin observed that many species are
endemic
Evolution of Populations
Chapter 23
Population genetics
• How do populations change (genetically)
over time?
• Gene pool – total of all genes in a
population
• Alleles – alternative forms of a gene
– Remember in sexual spp. One gene from
mom, one from dad
Mendelian
Genetics
Review
Mechanisms of Variation
• Mutations – changes in nucleotide
sequence of DNA
– Only mutations gametes passed to offspring
– Point mutations - single base change
– Chromosomal mutations - large scale
deletions, disruptions or rearrangements
• Also gene duplication (eg detecting odors)
– Mutation rates usually low in animals but
much higher in prokaryotes (eg. HIV)
Mechanisms of Variation
• Sexual recombination
– Rearranges alleles into new combinations
each generation (review Chap. 13)
– Remember, one chromosome of each pair
from each parent
– Do bacteria have sex? YES!
• What does THAT look like?
Sexual reproduction
• Two parents give rise to offspring that have unique
combinations of genes inherited from the two parents
Crossing Over (Not on Exam)
– Produces recombinant chromosomes with genes derived
from two different parents
Prophase I
of meiosis
Nonsister
chromatids
Tetrad
Chiasma,
site of
crossing
over
Metaphase I
Metaphase II
Daughter
cells
Figure 13.11
Recombinant
chromosomes
Also Independent Assortment (not on exam)
– Each pair of chromosomes sorts maternal and paternal
homologues into daughter cells independently of the other
pairs
Key
Maternal set of
chromosomes
Possibility 1
Possibility 2
Paternal set of
chromosomes
Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
Daughter
cells
Figure 13.10
Combination 1
Combination 2
Combination 3
Combination 4
How populations change
• Natural selection
– Variants better suited to the environment tend
to produce more offspring
• Or → Genetic drift – population changes
unexpectedly
Genetic drift – unpredictable changes
How populations change
• Genetic drift can come about through:
• Bottleneck effect; a few survivors
• Founder Effect
– A few individuals form an isolated population
How populations change
• Gene Flow
– Movement of fertile individuals or gametes
(eg. Pollen) into or out of a population
• Egs, pollen, storms or tsunami’s etc.
– Think humans and travel
Adaptive Evolution and Variation
• Genetic Variation can be:
– Discrete characters (either/or)
– Quantitative characters (vary along
continuum)
• Measuring variation
– Average heterozygosity (eg. Fruit flies 1800
out of 13,000 gene loci,)
– Nucleotide variability, in humans ~0.1% of
DNA bases
Variation between populations:
- Geographic variation in
a species can follow a
cline (variation in trait that
parallels environmental
gradient)
Fitness
• – contribution individual makes to gene pool
of next generation
• Relative fitness – contribution of one
genotype compared to alternative at same
locus
• based on reproductive success ONLY
How does natural selection work?
• Directional selection
– Favors extremes at one end of distribution
Modes of selection
Natural Selection, again
• Disruptive selection
– Favors extremes at both ends of distribution
Modes of selection
Natural Selection, again
• Stabilizing selection
– Removes extremes and favors intermediates
(most common type)
Modes of selection
Preserving variation
• Most eukaryotes are diploid (2 copies of each
chromosome/gene)
• Homozygous – identical genes at a location
• Heterozygous – different genes
• Heterozygote advantage – sickle cell anemia
How is it preserved?
• Wouldn’t natural selection remove all
unfavorable genotypes?
• No, due to:
– Recessive alleles
– Heterozygote advantage (eg sickle cell)
– Neutral variation (really neutral?)
Hardy-Weinberg Theorem
• Used to model non-evolving gene pools
• Can be used to determine allele frequencies
within a population
– Or, what is happening to variation in a population
• What is H-W good for?
H-W Theorem
• - frequencies of alleles and genotypes in gene
pool remains constant from generation to
generation if only Mendelian segregation and
recombination of alleles happens
• Requires:
– Extremely large population size
– No gene flow
– No mutations
– Random mating
– No natural selection
H-W and Sickle cell anemia
(no math on exam)
• Eg. In some populations the sickle cell
allele is 20% of all hemoglobin alleles
• H-W p2 + 2pq + q2 = 1
p = normal hemoglobin (0.8 of population)
q = mutant hemoglobin (0.2 of population)
p2 = (0.8)(0.8) = 0.64 or 64% of population
q2 = (0.2)(0.2) = 0.04 or 4% population
2pq = 2(0.8)(0.2) = 0.32 or 32% of population
What if?
• Malaria eradicated
– Change in natural selection?
– Loss of heterozygote advantage?
– Increase in gene flow?
Sexual selection
• Why sex anyway?
– Lower reproduction rate than asexual
– Provides variation for future
selection/adaptation
– Can provide short-term variation for disease
resistance
Sexual selection
can lead to differences
between sexes
Sexual Dimorphism
• If sexual characteristics increase mating
success then benefit outweighs risk
– “showy alleles” increase
– Egs. Horns, coloration, displays
The Evolution of Perfect Organisms:
Why doesn’t it happen?
•
•
•
•
•
What is perfect?
Evolution is limited by historical constraints
Adaptations are often compromises
Chance and natural selection interact
Selection can only edit existing variation