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CH's 22-24 (Descent With Modification (CH 22) (Charles Darwin…
CH's 22-24
Descent With Modification (CH 22)
Evolution = descent with modification = change in genetic composition from generation to generation
Greek philosophers first thought that life changed gradually over time
Aristotle, however, thought that eaxh life form was permanent and unchanging
these ideas aligned with the Old Testament in the Bible
Carolus Linnaeus was aligned with the Old Testament beliefs and also came up with our current system for naming organisms (
Homo Sapiens
for example)
A century later, Darwin said the organisms should be named based on evolutionary relationships
Darwin used fossils to support his ideas
Fossils are found in layers of sedimentary rock (strata)
Paleontology- the study of fossils
developed by Georges Cuvier
he noticed that lifeforms often changed, disappeared, or appeared over time
Charles Darwin
Born in 1809 (sam year Lamarck publishes his hypothesis on evolution)
travels the world on the HMS Beagle 1831-1836
writes his essay on descent with modification (evolution) 1844
publishes the
Origins of Species
1859
His ideas were strongly influenced by Hutton, Lamarck, Lyell, and fossils
Lamarck came up with principles that strongly influenced Darwin
Use and Diuse
Theory that says that useful body parts were enlarged while useless body part shriveled up
Inheritance of Acquired Characteristics
an organism will pass its modifications down to its offspring
Darwin's Research
He started out in medical school but ended up becoming a clergyman instead
his botany professor introduced him to the captain of the HMS Beagle
Darwin decided to go on a voyage with the captain was there to map the coastline of South America
Darwin spent most of his time collecting and observing plants and animals
he noticed that each creature was suited for their environment and that geologically speaking, the Earth is much older than people had originally thought
The Beagle made a stop at the Galapagos Islands and there, he noticed that all of the creatures suited for their environment but different on every island
this discovery led to his discovery of adaptations
adaptation- inherited characteristic that helps an organism survive and reproduce
which later led to his theory on natural selection
When he came home from his voyage he continued to build on the ideas he had during the voyage and even wrote an essay on them
he was hesitant to publish due to the outcry that his theory would cause
he was encouraged to publish before his thunder got stolen but he didn't listen until it was ALMOST too late
he reacted by quickly finishing and publishing his book in 1859
Main Ideas from Darwin's Book
descent with modification
life is unified through one ancestor organism that lived in the past
led to the diversity we see in life today
extinctions are not uncommon
Artificial/Natural Selection and Adaptations
Artificial Selection - the intentional breeding of plants or animals to produce desired traits
this is what he discussed first
after he talked about artificial selection, he talked about natural selection
he said that the environment determines which traits are desirable
argument was based on 2 observations
organisms in a population often have different traits
all species produce more offspring that the environment can support
this idea came from Thomas Malthus
Natural selection takes time whereas artificial selection can happen in relatively short period of time
INDIVIDUALS DO NOT EVOLVE
There is a lot of evidence for evolution
Direct observations
Natural slection when a new species is introduced
soapberry bugs have long "beaks" to get their food
when a new food source was introduced, which required a short "beak", those with a short beak survived
drug resistant bacteria
Homology- similar structure, different function
mammals have the same arrangement of bones in their limbs
vestigial structures often arise from this dilemma (snakes still have a pelvis for example)
all life forms have a similar genetic code
convergent evolution- when distantly related organisms look similar but for different reasons
traits are analogous rather tha homologous in this case
Fossils
fossils document the pattern of evolution
they also show us where new types of organisms come from
Biogeography- the study of the geographic distributions of species
organisms are influenced by many geographic factors
continental drift being a big one
endemic- native to a certain area and not found anywhere else in the world
common on islands
the are commonly closely related to the organisms on the mainland
Evolution of Populations (CH 23)
The smallest unit of evolution is a population.
Microevolution
Genetic Variation = phenotypic variations
Individuals have different inherited traits (variation) and natural selection acts on these variations
some traits are determined by one gene and are on an either-or basis where as others are determined by multiple genes
Darwin knew that individual variation is required for evolution but he didn't know how these traits got passed on
Mendel discovered that individuals pass on their traits through genes
A lot of genetic variation can be seen in DNA but not so much of it is seen in phenotypic variation
this is due to introns (non-coding DNA chunks)
Sources of variation
New Alleles
new allele = mutation
is, for the most part, harmful
removed quickly via natural selection sometimes
in most cases, harmful alleles that are recessive are hidden from natural selection
neutral variation = mutations that aren't harmful
Altering Gene Number or Position
usually harmful
sources
meiosis errors (unequal crossing over)
slippage during DNA replication
transposable elements
chromosome duplication
Rapid Reproduction
mutation rates in prokaryotes are higher for this reason
Sexual Reproduction
unique combinations of alleles
three places where allele shuffling can occur
crossing over
independent assortment of chromosomes
fertilization
Hardy-Weinberg Equation
Gene Pools and Allele Frequencies
population= a group of individuals that live in the same area and can interbreed and produce fertile offspring
gene pool= a population's genetic makeup
every allele has a proportion or frequency in the population
Hardy-Weinberg Equation
p^2 + 2pq + q^2 = 1
Achieving Equilibrium Conditions
no mutations
random mating
no natural selection
extremely large population
no gene flow
Applications
determining weather a population is evolving
what percentage of a population is carrying a genetic disease
Natural Selection, Genetic Drift, and Gene Flow
Natural Selection
individuals have variations and those who are better suited to the environment have more offspring
adaptive evolution = good traits increase in frequency over time
Genetic Drift = when allele frequencies fluctuate
especially common in smaller populations
Founder Effect = a small group gets cut off from the rest of the population and therefore the gene pool is different
Bottleneck Effect = sudden change in environment greatly reduces population size and thus genetic variation is reduced
significant in small populations
causes allele frequencies to change at random
leads to a loss of variation
can cause harmful alleles to become fixed
Gene Flow = transfer of alleles into or out of a population
usually caused by a fertile individual moving around
Natural Selection Consistently Causes Adaptive Evolution
natural selection is not random
Relative Fitness = how many offspring an individual has
Types of Selection
Directional = favors individuals whoa re representing the extreme of a phenotype
Disruptive = when conditions favor individuals at either extreme of of a phenotype
Stabilizing = when conditions favor individuals who fall in the middle of a phenotypic range
Sexual = where some individuals of the same sex are more likely to obtain a mate than others
Sexual Dimorphism = males and females are different
Intrasexual = same sex competes directly for a mate
Intersexual = individuals of one sex choose their mate from the opposite sex
Adaptive Evolution is a continuous process
Balancing selection
Frequency-Dependent Selection = fitness of a phenotype depends on how common it is
Heterozygote Advantage = heterozygotes are more fit than either homozygote possibility
Why there's no such thing as perfect
selection only exists on existing variations
evolution is limited by historical constraints
adaptations are compromises
chance, natural selction, and the environment interact
Origin of Species (CH 24)
The Biological Species Concept and Reproductive Isolation
Biological Species Concept = a group of populations that can breed and have fertile offspring
the gene pool of a species stays together by gene flow
Limits of this concept
doesn't include fossils or asexual species
species are designated based on the assumption that no gene flow is occurring
Reproductive Isolation = biological barriers that prevent individuals of different species from mating
limits that formation of hybrids
Prezygotic = before the zygote
Habitat Isolation = 2 species live in different habitats
Temporal Isolation = species that breed at different times can't mate
Behavioral Isolation = courtship rituals that only work with one species
Mechanical Isolation = morphological differences prevent mating
Gametic Isolation = sperm of one species can't fertilize an egg of another species
Postzygotic = after the zygote
Reduced Hybrid Viability = impairment of the hybrids development and/or survival
Reduced Hybrid Fertility =m the hybrid can't have any offspring of its own
Hybrid Breakdown = the first generation is fine but the second generation is either feeble sterile
Other Definitions
Morphological = based on shape and structure
Strength
applies top asexual individuals
Weakness
based on subjective criteria
Ecological = based on niche
Strengths
applies to asexual individuals
Empathizes disruptive selection
Weakness
Something could be of the same species but have different niches
Speciation Happens With or Without Geographic Separation
Allopatric Speciation = occurs when a population is geographically separated
process
geographic isolation
different mutations/ natural selection/ genetic drift
reproductive isolation
Evidence?
the 30 species of snapping shrimp
Sympatric Speciation = occurs when a species lives in the same area but they don't mate
very rare
polyploidy
extra sets of chromosomes
allopolyploid = when a sterile hybrid becomes fertile
sexual selection
habitat differentiation
occurs when a sub-population uses resources that the parent population doesn't
Hybrid Zones = an area in which different species meet and mate
Patterns Within Hybrid Zones
some are narrow bands
typically found where two habitats meet
Hybrid Zones and Environmental Changes
with change comes either a relocation of hybrid zones of formations of new ones
Hybrid Zones Over Time
hybrids becoming re-productively isolated from parent species = new species
reinforcement of barriers
strengthening of prezygotic barriers due to natural selection
stronger for sympatric populations
species fusion
weakening of reproductive barriers
reverses the speciation process
stability
hybrids continue to be produced even if they are naturally selected against
Speciation Tempo and Amounts of Genetic Changes
Time Course of Speciation
The Fossil Record
many cases where new species suddenly pop up or where a species has been around for awhile and the suddenly disappears
Punctuated Equilibria = a period of stability followed by sudden change
Gradual Model = species diverge from one another slowly and over time
Speciation Rates
punctuated = rapid change
typically ranges from 4,000 - 40,000,000 years to form a new species with average time being 6,500,000 years
Speciation Genetics
change can be as small as one gene to cause reproductive isolation
Speciation eventually leads to macroevolution