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Chapters 22-24 (Chapter 23: The Evolution of Populations (Concept 23.4:…
Chapters 22-24
Chapter 23: The Evolution of Populations
Populations change over time not the individuals
Microevolution: change in allele frequencies in a population over generations
Concept 23.1: Genetic variation makes evolution possible
Genetic Variation:
differences among individuals in the composition of their genes or other DNA sequences.
flower colors of Mendel's pea plants
determined by a single gene locus, with different alleles
At the gene level, can be quantified the average percentage of loci that are heterozygous
genetic variation can also be measured at the molecular level
nucleotide variability occurs within introns
body builders can alter their phenotypes but can pass on huge muscles
Formation of new alleles
can arise by mutation: a change in the nucleotide sequence in an organism's DNA
harmful alleles in diploid organisms that are recessive can be hidden from selection
Neutral Variation
: differences in DNA sequence that do not confer a selective advantage or disadvantage
only mutations in cell lines that produce gametes are passed on
Altering Gene Number or Position
Chromosomal rearrangements are beneficial
translocation of chromosomes have a positive effect
prokaryotes have many generations per unit of time
mutations can quickly generate genetic variations
also can be very true for viruses
Concept 23.2: The Hardy-Weinberg equation can be used to test whether a population is evolving
Gene Pools and Allele Frequencies
population: individuals of the same species that live in the same area and produce fertile offspring
may be isolated geographically
gene pool: consists of copies of every type of allele at every locus in all members of the population
alleles can be
fixed
, with all organisms being homozygous for that allele
if two or more alleles are present, then individuals are either homozygous or heterozygous
Hardy-Weinberg Equilibrium
p
represents the frequency of one allele and
q
represents another
consider all of the alleles in all of the crosses in a population
"reproduction" basically randomly selects alleles from a "bin"
no gene flow in population
allele is not sex linked
population must be very large
p + q = 1
p^2 +2pq + q^2 = 1
Concept 23.3: Natural Selection, genetic drift, and gene flow can alter allele frequencies in a population
based on differential success in survival and reproduction
those with the heritable traits best suited to their environment then to produce more offspring than those with traits that are not as well suited
adaptive evolution:
a process in which traits that enhance survival or reproduction tend to increase in frequency over time.
Genetic Drift
chance events causing allele frequencies to fluctuate unpredictably from one generation to the next
Founder Effect
individuals become isolated from a larger population, the smaller group will establish a new population with a difference in the gene pool from the original
responsible for certain inherited disorders among isolated human populations
Bottlneck Effect
sudden change in the environment, such as a fire or flood
the population passes through a "bottleneck"
Gene Flow: transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes
Concept 23.4: Natural selection is the only mechanism that consistently cause adaptive evolution
Relative Fitness
the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals.
a moth producing more offspring because of its body color conceals it form predators
Directional Selection: conditions favor individuals exhibiting one extreme of a phenotypic range
Disruptive selection: conditions favor individuals at both extremes of a phenotypic range over individuals with intermediate phenotypes
Stabilizing Selection: acts against both extreme phenotypes and favors intermediate variants
Selection favors whoever can reproduce the most
Sexual Selection
individuals with certain inherited characteristics are more likely the others of the same sex to obtain mates
intrasexual selection: individuals of one sex compete for mates pf the opposite sex
intersexual selection: individuals of one sex are choosy in selecting their mates from the other sex
Balancing Selection: includes frequency-dependent selection and heterozygote advantage
Frequency-Dependent Selection: fitness of the phenotype depends on how common is in the population
Why Natural Selection Cannot Fashion Perfect Organisms
Selection can act only on existing variations
Evolution is limited by historical constraints
Adaptations are often compromises
Chance, natural selection, and the environment interact
Chapter 24: The Origin of Species
Speciation
The "mystery of mysteries" that captivated Darwin
process by which one species splits into two or more species
produced the diversity of life
Microevolution: changes over time in allele frequencies in a population
Macroevolution: pattern of evolution above the species level
origin of new groups of organisms
The biological species concept emphasizes reproductive isolation
a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring-cannot produce viable fertile offspring with other groups
Reproductive Isolation
the existence of biological factors that impede members if two species from interbreeding
these barriers can limit the formation of hybrids or offspring that form due to interspecific mating
Prezygotic Barriers: impede mating or hinder fertilization if mating does occur
Habitat Isolation
Temporal Isolation
Behavioral Isolation
Mechanical Isolation
Gametic Isolation
Postzygotic Barriers: prevent a hybrid zygote from developing into a viable, fertile adult
Reduced Hybrid Viability
Reduced Hybrid Fertility
Hybrid Breakdown
Morphological Species Concept
distinguishes a species by body shape and other structural species
can be applied to asexual and sexual organisms
Ecological Species Concept
defines a species in its ecological niche
can accommodate asexual and sexual species
Speciation can take place with or without geographic separation
Allopatric speciation
gene flow is interrupted when a population is divided into geographically isolated subpopulations
water level in a lake may subside, resulting in multiple smaller lakes that now have separated populations
can occur without geologic remodeling
if geographic isolation occurs, gene pools may diverge
Sympatric Speciation
"Same Country"
can occur if gene flow is reduced by polyploidy, sexual selection, and habitat differentiation
Polyploidy
a species originates from an accident during cell division
occasionally occurs in animals
two distinct forms of polyploidy are observed in the plant population
autopolyploid: more than two chromosome sets that are all derived from a single species
allopolyploid: fertile when mating with each other but cannot interbreed with either parent species
represent a new biological species
Sexual selection can be driven by sympatric speciation
Example: Cichlid Fish choosing their mate based on male coloration also acting as reproductive barrier
Hybrid zones reveal factors that cause reproductive isolation
region where members of different species meet and mate, producing at least some offspring of mixed ancestry
some zones form as narrow bands like with the yellow-bellied toad and fire-bellied toad
located wherever the habitats of the interbreeding species meet
change in environment could result in where the species meet
existing hybrid zone can then move to a new location or another zone may form
Reinforcement: natural selection should strengthen prezygotic barriers to reproduction, reducing unfit hybrids
barriers should be stronger for sympatric populations than for allopatric populations
Chapter 22: Descent with Modification: A Darwinian View of Life
Concept 22.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species.
Scala and Naturae and Classification of Species
evolution: descent with modification
life forms can be arranged on a ladder, or scale of increasing complexity
Carolus Linnaeus developed the binomial format for naming species
grouped similar species into increasingly general categories
Darwin argued that classification should be based on evolutionary relationships.
Ideas About Change over Time
fossils are the remains or traces of organisms from the past
Paleontology is the study of fossils and was developed by for the most part by French scientist Georges Cuvier.
Cuvier staunchly opposed the idea of evolution.
James Hutton and Charles Lyell both had other ideas of how change happened over time.
Their ideas strongly influenced Darwin's thinking
Lamarck's Hypothesis of Evolution
Proposed how life changes over time
used two principles that were widely accepted at this point in time
1)
Use and Disuse
2) Inheritance of Acquired Characteristics
Concept 22.2: Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity of life
Darwin's Reasearch
Darwin went to school first to be a medical doctor
After graduating from Cambridge he accompanied Captain Robert Fitz roy on the HMS Beagle for a voyage around the world.
The Voyage of the Beagle
primary mission of the voyage was to chart poorly known stretches of the South American coastline
Darwin spent his time observing and collecting plants and animals
Darwin observed on the Galapagos Islands birds that looked similar to each other but were different in species
Adaptations: inherited characteristics of organisms that enhance their survival and reproduction in specific environments
The Galapagos finches and their beak size
Natural selection: a process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than do others because of those traits
Darwin wrote and published his book
On the origin of Species by Means of Natural Selection
in 1859.
Descent with Modification
Darwin attributed the unity of life to the descent of all organism from an ancestor that lived in the past
Darwin also believed that the descendants living in certain habitats accumulated adaptations to fit their way of life
Darwin viewed the history of life as a tree, with multiple branches
Artificial Selection
Humans modifying other species over many generations by selecting and breeding individuals that possess desired traits
animals often bear little resemblance to their ancestors because of this
Darwin's observations and inferences
Observation 1) members of a population often vary in their inherited traits
Observation 2) All species can produce more offspring than their environment can support and many of these offspring fail to survive and reproduce
Inference 1) Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than do other individuals
Inference 2) This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations.
Darwin began to make connections to these inferences after reading an essay by economist Thomas Malthus
realized that the characteristic to overreproduce was of all species
Concept 22.3: Evolution is supported by an overwhelming amount of scientific evidence
Soapberry bugs feeding on the balloon and the goldenrain tree
researchers study beak lengths evolution in soapberry bug populations that feed on plants introduced to Louisiana, Oklahoma, and Australia.
The Evolution of Drug-Resistant Bacteria
bacteria and viruses can produce new generations in a short period of time
MRSA strains can exchange their genes to become more resistant
Natural Selection is a process of editing
Natural selection also depends on time and place
Homology: similarity resulting from common ancestry
Anatomical and Molecular Homologies
forelimbs of all mammals show the same arrangement of bones even if the appendages have different functions
Homologous Structures
: various on a structural theme that was present in a common ancestor
Vestigial Structures:
remnants of features that served a function in the organism's ancestors
Humans and bacteria share genes from a distant common ancestor
evolutionary tree:
diagram that reflects evolutionary relationships among groups of organisms
A Different Cause of Resemblance: Convergent Evolution
convergent evolution: independent evolution of similar features in different lineages
sugar gliders in Australia are very similar to the flying squirrel
analogous features share similar function but not common ancestry
Biogeography
study of the geographic distributions of species
is associated with continental drift and where fossils can be found
Endemic: found nowhere else in the world