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98 Cards in this Set

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What must be present for Natural Selection to occur?
1. Individuals vary in most or all traits
2. At least some of this variation is heritable
3. More offspring are born than survive to reproduce, and there is variability among individuals in reproductive output
4. Reproductive output is non-random, tied to variation
What are the mechanisms of Natural Selection?
Natural Selection acts on individuals, but its consequences occur in populations.
Natural selection acts on phenotypes, but evolution consists of changes in allele frequencies.
Natural selection is not anticipatory.
Natural selection acts on existing traits, BUT new traits can evolve.
Natural selection does not lead to perfection.
Natural selection is non-random, but it is not progressive, forward-looking.
What is Reassortment?
Randomness in which of each pair of chromosomes is packaged into a given sex cell, and which sex cells combine to form a zygote
What is Recombination?
During meiosis, crossing over between homologous chromosomes yields new combinations of alleles on individual chromosomes
What are the different mutations?
Point mutations
Gene duplication
Chromosomal inversions
Genome duplication
What is a point mutation?
replacement of a single base nucleotide with another nucleotide of the genetic material, DNA or RNA. Often the term point mutation also includes insertions or deletions of a single base pair.
Explain Mutation Rates.
Low for a given site.
C. elegans exhibits 2.1 x 10-8 per site per generation (that’s a 1 in 48 million chance!)
High for the entire genome (multiply rate by number of bases in whole genome.)
Lower in asexually reproducing species, higher in sexually reproducing species.
Generally neutral but can be detrimental.
What causes gene duplication?
Retrotransposition
Unequal crossing over
What is Retrotransposition
mRNA is reverse-transcribed into DNA, segment may be inserted into a chromosome
What is Unequal crossing over
During meiosis, improper synapsing occurs, one chromosome left with deletion; the other left with two copies of some genes. Remember Charcot-Marie-Tooth disease (Ch. 2, p. 57)
What happens to duplicated genes?
Duplicated genes may lack promotors and other regulatory elements, then they serve no real purpose.
Mutations can accumulate rapidly because there is no selection pressure against their phenotype (they have no phenotype).
If duplicated genes are functional, they are also subject to mutation.
What is a Chromosome Inversion?
Massive change in the organization of genetic material.
Double-stranded DNA breaks can be repaired; sometimes occurs with segment of chromosome inverted. Forms super genes.
What can result in genome duplication?
Autopolyploidy: multiplication of genome within a species.
Meiosis fails, 2N gametes produced
4N offspring result, particularly if self-fertilization possible

Instantaneous (single generation) speciation!
What is the HWE?
A mathematical description of the genetic (and therefore phenotypic) make-up of a population. A method for determining whether a population’s genetic structure is changing over the course of successive generations
What results from HWE?
Genotype frequencies remain the same from generation to generation
If allele frequencies are know, genotype frequencies can be calculated
Genotype frequencies remain the same from generation to generation
What is required for HWE?
No new mutation
No migration
No selection
No genetic drift
Random mating
What are the effects of selection in regard to HWE?
Change in genotype frequency, Change in allele frequency
Even small selection pressures can have significant effects over time
What is Frequency-dependent selection?
Occurs when selection pressure depends upon frequency of the phenotype in the population
What is the Heterozygote advantage?
Also called heterozygote superiority
Also called overdominance
Heterozygotes have higher fitness than either homozygote
This is the case with sickle cell anemia: competing selection pressures against both homozygotes maintains sickle cell allele in the population though it is a very harmful mutation
Maintains genetic diversity in populations
What is the Heterozygote disadvantage?
Also called underdominance
Heterozygotes selected against, one homozygote likely has greater fitness than the other
Leads to allele fixation
Leads to loss of genetic diversity in populations
What is the role of mutation?
Even a very high mutation rate produces a very small change in allele and genotype frequencies .
However, mutation is the basis for new variation in populations, variation upon which natural selection can act!
Law of segregation
parents contain two copies (“alleles”) of each gene; a gamete receives only one of those two copies
Law of independent assortment
different alleles/traits are inherited independently from each other; alleles of the same gene assort independently during gamete formation
What are p and q in the HWE?
Knowing p and q, frequencies of genotypes expected can be calculated
What is the role of migration in evolution?
Migration means alleles move from one place (population) to another
Can change allele frequencies in populations
Especially important in small populations such as island an adjacent to mainland
Movement from or to mainland has little effect on large mainland population
Movement to or from island can have big effects on the small island population
Migration changes population genetic make-up
Migration prevents divergence of populations from each other
Explain genetic drift.
change in allele frequencies because of
(1) randomness in allele packaging into gametes,
(2) randomness in which gametes produce offspring, and/or
(3) randomness in the chance survival and reproduction of individuals
What is the difference between selection and genetic drift?
Selection is differential reproductive success for a reason. Genetic drift is differential reproductive success that just happens.
How does genetic drift affect different population sizes?
Effects of genetic drift are greater as population size decreases.
Genetic drift happens faster in smaller populations.
With sufficient time, genetic drift can have dramatic effects (including allele fixation/allele loss), even in large populations
What is neutral theory?
Proposes that advantageous mutations are very rare
Almost all new alleles are selectively neutral
The rate of evolutionary change equals the rate of new mutation
What is selectionist theory?
Advantageous mutations do occur with some frequency
They occur often enough that they do play a role in evolution
Advantageous mutations lead to evolution through natural selection
Note: disadvantageous mutations also occur, but are eliminated by natural selection. Not completely true… remember:
Cost-benefit analysis: some alleles are costly in some situations, but maintained by selection under other conditions (i.e. sickle cell)
Deleterious mutations can persist in heterozygous form
What happens when mutation, genetic drift and natural selection interact?
New harmful alleles are generated; these may be eliminated by natural selection
Neutral mutations occur and are fixed or lost by chance (genetic drift)
Advantageous mutations can occur, and may become fixed because of natural selection
How does inbreeding effect evolution?
Inbreeding increases frequency of homozygotes and decreases frequency of heterozygotes relative to what would be expected under HWE.
Inbreeding yields loss of genetic diversity
What is inbreeding depression?
Generates offspring homozygous for deleterious alleles, reduced fitness. Fix problem with migration!!
What is adaptation?
Process whereby a population becomes better suited to its habitat. Adaptations are not perfect- they are constrained and there are trade-offs
How is adaptation tested?
Careful design of control groups
Making sure that all experimental tests are conducted in the same manner to avoid bias and increase precision
Randomization of treatments to avoid bias and increase precision
Repetition on large sample size
Replication of entire experiment
Why is Phenotypic plasticity important?
It is a trait that can be acted upon by natural selection (phenotypic plasticity must have a genetic basis, and it can be selected for or against… or evolve by other means)
It illustrates that the function of a trait can change over time
What is Phenotypic plasticity?
The ability of an organism to change its phenotype in response to changes in the environment.
What is Sexual dimorphism?
The systematic difference in form between individuals of different sex in the same species.
What is sexual selection?
A form of selection that drives the production of sex-based differences within a species
According to our text sexual selection is: “differential reproductive success due to variation among individuals in success at getting mates”
How does parental investment affect sexual selection?
When one sex invests more in reproduction than the other, success of the heavily investing sex is limited by resources and time.

Success of the lightly investing parent is limited by number of mates.
What 2 issues drive differences between sexes in sexual selection?
Relative amount of parental investment
Operational sex ratio: the effective number of each sex available for mating (female mammals carry young and usually care for young; during these times, the female is unavailable for mating so there is a male-biased operational sex ration in a 50% male, 50% female population)
What are the consequences of sexual selection?
The sex that invests more and is operationally rare is the one that chooses mates (usually female)
The sex that invests less and is operationally more common is the one that competes for mates (usually male)
Therefore, the competitor sex is subject to strong sexual selection, and the chooser sex is subject to weak sexual selection
What is the difference between Intrasexual selection?
Intersexual selection?
Intrasexual selection: Male-male combat

Intersexual selection: Female choice among males
What is direct fitness?
an individual’s own reproduction
What is indirect fitness?
additional reproduction of an individual’s kind of alleles because that individual acts to increase reproductive output of relativ
What are the 2 mechanisms of kin selection?
Alleles favored by kin selection rise to high frequency because they increase fitness of individuals likely to be carrying those same alleles (i.e. close relatives)
The Greenbeard Effect: alleles rise to high frequency by inducing altruism toward individuals certain to be carrying the same alleles
What is kin selection?
Natural selection that favors the spread of alleles that increase the indirect component of fitness (reproduction of your kind of alleles rather than your own actual alleles)
What is Eusociality?
represents a dramatic form of kin selection in which many individuals (most of a colony) are 100% non-reproductive, but support reproduction by the queen
What is the Haplodiploidy hypothesis?
According to kin selection theory, females should invest more in supporting their sister queen than in production of their own offspring (they should maximize their inclusive fitness by acting as reproductive altrusits)
Problem: not all haplo- diploid species are eusocial, and not all eusocial species are haplodiploid
What factors influence eusociality?
High predation rates
Carnivore in larvae
Larvae that are largely immobile
Building of complex nests
Long-term parental care
Individuals who breed alone are unlikely to live long enough to bring offspring to maturity
What is altruism?
behaviour by an individual that increases the fitness of another individual while decreasing the fitness of the actor
How is the upcoming flu infection predicted?
the one with the most non-synonymous substitutions in the 18 codons known to be under selection pressure
What is the theory for cross-species transmission of the flu?
Dual infection of pigs by human and bird strains
Formation of “hybrid” flu strians by gene swapping
Infection of people by the new “hybrid strain
Summarize bacteria resistance to antibiotics.
Bacteria can evolve resistance to antibiotics (remember from Ch. 1 that viruses evolve resistance to drug treatment as well)
Evolution of resistance is not without cost to the bacteria
Bacteria can experience secondary mutations that alleviate the costs of resistance (evolution of “superbugs”)
The best defense against antibiotic resistance is to avoid letting bacterial populations evolve resistance in the first place (see p. 541 for how to do this)
What is Virulence?
Harm done by a pathogen to its host
What are the 3 models for virulence?
Coincidental evolution
Short-sighted evolution
Trade-off hypothesis
What is Coincidental evolution
pathogen’s virulence is a by-product of evolution elsewhere (botulism in soil; not evolved as a human neurotoxin)
What is Short-sighted evolution
evolution of traits within a host, but these traits are unlikely to be passed on to other hosts (poliovirus: doesn’t normally invade nervous system; mutants that do are not passed on to new hosts). In a sense, many pathogens are short-sighted. HIV, for example, evades the host’s immune system by infecting immune cells. But this hastens the host’s death.
What is the Trade-off hypothesis
natural selection should favor pathogens that strike an optimal balance between costs and benefits of harming their hosts. Selection should favor parasites that reproduce quickly inside host until the parasite load becomes severely harmful to the host).
What is Allopatric speciation?
biological populations are physically isolated by an extrinsic barrier and evolve intrinsic (genetic) reproductive isolation, such that if the barrier should ever vanish, individuals of the populations can no longer interbreed.ift
no interbreeding
potentially different selection pressures
What are some concepts of the founder hypothesis?
Closely related species should be found in adjacent isolated geographic areas
Phylogeny and geographic distribution should correspond with order in which islands formed
What is Parapatric Speciation?
A species evolves into two across geographic range without intervening barrier
hypothesized primarily because of the existence of "hybrid zones" between different forms of an organism
or
species diverged by allopatric speciation, and then the two new species later came back together
What is reinforcement in regard to parapatric speciation?
something that drives species it at the hybrid zone
hybrids are relatively less fit
hybrids are selected against
What is Sympatric Speciation?
may occur when there are multiple niche polymorphisms (different forms each better suited for a particular niche)
these occur when there is non-gaussian resource distribution
must involve assortative mating
What are the 3 steps to speciation?
Isolation
Divergence
Secondary contact with either:
completion of divergence (speciation)
elimination of divergence (breakdown)
What drives divergence?
Genetic drift
Sexual Selection
Natural selection
What happens when isolated taxa come back together?
hybridization
What is LUCA?
Last Universal Common Ancestor: The most recent common ancestor of all living things is the organism whose immediate descendants diverged to found the lineages that ultimately became all extant organisms.
What arose first, DNA or protein and why?
Neither! Proteins can do many things; they provide phenotype. But they cannot store and transmit information; they cannot reproduce
DNA can store and transmit information, but it cannot perform work
What facts support RNA as the first start for life?
Ribosomes are the most conserved and universal components of the information transmitting machinery
Ribosomal proteins exist on a framework of RNA
The RNA within ribosomes is the actual catalytic portion of the protein synthetic machinery
Accessory RNA (tRNA) is required for ribosomes to function
Other ribonucleosides are critically important to all aspects of cellular function in all species:
What is the Panspermia hypothesis?
life, or at least its building blocks, came from elsewhere in the universe
Murchison meteorite fell to Earth on Sept. 1969 in Murchison, Australia
Contained equal amounts of L- and D-forms of at least 5 essential amino acids
Other meteorites have since been recovered that contain similar biological building blocks
What is the Oparin-Haldane hypothesis?
building blocks of life were formed on early Earth from existing organic precursors
What is the Universal gene-exchange pool hypothesis?
Rampant exchange of genetic material among taxa until bacteria, archaea and eucaria emerge
What is the Ring of life hypothesis?
Bacteria and archaea evolved; eucaria form from fusion of a bacterian and a eucarian
What is the Chronocyte hypothesis?
Bacteria/ archaea evolve as one lineage separate from eucaria, then a eukaryote engulfs an archaean to form nucleus
What is the Three viruses, three domains hypothesis?
Viruses predate cellular life, come from the RNA world
Viruses infected RNA-based cells, evolved DNA to prevent destruction by host
DNA-based viruses became part of cells
How is RNA capable of self replication?
In experiments, RNA accumulates mutations over time
These mutations decreased an RNA virus’s ability to infect E. coli
Therefore, mutations led to a change in phenotype
In another experiment, catalytic RNA was involved in a loop of reproduction requiring DNA as an intermediate
Catalytic RNA evolved to increase catalytic efficiency and therefore increase its rate of replication
What is the Cambrian Explosion?
apid appearance of most major groups of complex animals around 530 million years ago, as evidenced by the fossil record.[1][2] This was accompanied by a major diversification of other organisms, including animals, phytoplankton, and calcimicrobes. Before about 580 million years ago, most organisms were simple, composed of individual cells occasionally organized into colonies.
Why is the Burgess Shale (British Columbia) so important?
44 genera of arthropods
14 genera of trilobites
Extraordinary diversity, far greater than in any pre-cambrian stratum (pre-550 MYA)
What evidence shows earlier divergence in the Cambrian Explosion?
Bruce Runnegar (1982):
Used a molecular clock to date the origin of animal phyla
Considered differences among hemoglobin amino acid sequences
Calibrated genetic distances between vertebrate groups using fossils of known ages
Concluded that earliest branches (porifera, cnidaria, bilatera) occurred 900Mya, long before the defined start of the Cambrian

Wray, Levinton, Shapiro
Concluded chordates, echinoderms diverged 1 billion years ago
This is hundreds of millions of years before appearance in fossil record
Apparently complex vertebrates exist in lower Cambrian materials
What is the most supported theory for the KT extinction?
Microtektites
Shocked quartz
Massive impact crater (Chicxulub) at the tip of the Yucatan peninsula (dated to 65MYA)
Irridum spike:
rare on Earth, but common in meteorites
Massive spike at 65MYA
Clay zone between layers of limestone
Limestone from calcereous shells of marine invertebrates
Clay interruption from a time of few marine invertebrates
Began about 65MYA
What is punctuated equilibrium?
all morphological variation occurs at the time of a speciation (branching) event;
What is phyletic gradualism?
morphological change occurs gradually and is unrelated to speciation events.
What are some shared derived featured between humans and old world monkeys?
Shared derived features:
Large brain
Erect posture
Increased hip, ankle flexibility
No tail
What evidence supports that chimps are closest to humans?
immune profiles of serum albumin proteins
Mitochondrial genes, nuclear genes, many morphological features
Human/chimpanzee split 5.0-5.4 MYA
At nucleotide level, human and chimpanzee about 95% identical; much higher at protein sequence level
Big difference: apes have 24 chromosome pairs; people have 23, but solely because of chromosome fusion
What is the earliest known hominid and discuss it's features.
Sahelantropus is clearly very early
Much older (6-7MY) than molecular evidence suggests was the split among humans and chimpanzees (5MYA)
Discoverers argue that it is the common ancestor of humans and chimpanzees
Chimp-like cranium, flat face like humans
What features of Australopithecines point to a lineage of early human?
Many aspects of bone structure (hips, knees, foot structure, spinal column structure, limb proportions) all lead to conclusion of bipedalism
Another amazing piece of evidence: bipedal footprints fossilized in volcanic ash from 3.6MYA
How does being bipedal reflect Encephalization?
Bipedalism predates increased brain size
Increased brain size despite no significant increase in body size
What is Encephalization?
Increased brain size despite no significant increase in body size
What is runaway selection?
Elaboration of extreme characteristics
What is the relationship between how a disease is transmitted and it's virulence?
Virulence is lower in pathogens that do not have ready vectors other than the host itself. Pathogens transmitted by insect vectors or in water can be transmitted even if the host is severely disabled by the pathogen.
How does AIDS infect and thrive?
HIV infection requires two cell-surface proteins: CD4, CCR5
Found on various cells of the immune system: helper T-cells, dendritic cells, perhaps also macrophages and suppressor T-cells
Helper T-cells are critical- they ramp up immune responses by other cells such as B-cells and macrophages. Helper T-cell death means poor immune function
HIV replicates explosively at first, killing off CD4 T-cells
Immune system mounts a response, and HIV infection rate slows (fewer cells to infect!)
Immune system eventually crashes, AIDS sets in
What two lineages arose from Australopithecus?
1.7 MYA
robustus
gracile
What is the difference between robustus and gracile?
Gracile lineage
Smooth, rounded cranium
Forward-projecting face (prognathism)
Small brains (400-500cm3; modern humans 1300+cm3)
Robust lineage
Genus Paranthropus
Very large, highly prognathic faces
Very large cheek teeth
Cranium with crest for attachment of large muscles
Small brains (400-500cm3; modern humans 1300+cm3)
What is considered to be the "key ancestor" of humans and why?
Homo erectus in southeast Asia as much as 1.7 MYA
Homo ergaster in Africa 1.5-1.8 MYA
Larger brain size (H. ergaster: 850cm3)
Smooth cranium
Flat face
Smaller teeth
Intermediates between gracile australopithecines and “modern” human ancestors
How does AZT work?
AZT blocks reverse transcriptase function
Mimics thymidine, but cannot accept further nucleic acids
What evolutionary trait prevents AIDS infection in people?
CCR5-Δ32: naturally-occurring variant of the CCR5 receptor that contains a 32 base pair deletion
Appears to protect against HIV entry into T-cells
In areas where CCR5-Δ32 is common, HIV/AIDS is uncommon
Primates have high resistance to SIV, contain similar modifications of CCR5
CCR5-Δ32 may increase in frequency if non-carriers are selected against by HIV
What is Coevolution?
Interaction between species that lead to reciprocal adaptation