Midterm 1 Flashcards
Evolution
genetic change in a population
Natural Selection
consequence of certain individual organisms in population being born with characteristics that enable them to survive better and reproduce more than offspring of other individuals in population
4 principles of evolution
1) all life is linked through a common ancestor
2) Populations of living things change with time
3) Environment influences this change (through natural selection)
4) descent through modification
Charles Darwin
at age 16 he travelled to the Galapagos and studied finches (different beaks), armadillo fossils, plants and animals that differed from on the mainland
Traits exhibited by species (Darwin discoveries)
1) finches had different shaped beaks based on what their diet was
2) similarities based on fossils found and the living species around that area
Adaptation
biological definition: a trait that benefitted an organism in a particular environment
Fitness
an organism’s ability to survive or reproduce in a particular environment
3 important elements of fitness
1) fitness is measured relative to species’ genotypes and phenotypes
2) fitness depends on environment the individual lives in
3) fitness depends on reproductive success compared to other organisms in the same population
How does natural selection operate?
1) Variation in trait (different traits are present in individuals of same species)
2) mode of inheritance (must be on an allele in order for it to be passed on)
3) fitness consequences for trait (individuals with traits suited for reproduction generally leave more offspring)
Artificial Selection
process of humans choosing certain varieties of an organism over others
Evidence for evolution
1) Homologies
2) The Fossil Record
3) Biogeography
Direct observation
we can see evolution occurring in bacteria which have a short lifespan
Homology
similarity with ancestors:
Characteristics present in ancestral organism altered over time by natural selection as its descendants face different environmental conditions
Homologous Structures
anatomical similarities in different organisms
example: vertebrate embryos all have: tail posterior to the anus, pharyngeal (throat) pouches
Evolutionary tree
representation of patterns of descent
Vestigial Structures
organs or anatomical structures that have been retained during evolution even though they have lost some of their ancestral functions
ex: whales have vestigial structures that show evidence that they came from 4 legged ancestor
Analogy
presence of similar structures in evolutionary divergent lines of descent, because of similar environmental pressure
ex: bats, birds, butterflies all developed wings from different environmental pressures
Divergence
two evolving groups of recent common ancestry becoming more dissimilar
Convergence
two evolving groups of distant common ancestry becoming more similar
The Fossil Record
chronicle of evolution over millions of years of geologic time engraved in order in which fossils appear in rock strata
(fossils: physical evidence of ancient organisms)
Biogeography
Study of where things are distributed all over the world
(ie how animals adapt to their environments)
Phylogeny
evolutionary history of an organism and its relationship to other species
mapped out with phylogenic trees
Phylogenic trees (and their parts)
branches, node, rooted, basal taxon, sister taxa
branching of diversification is depicted
derived characters are marked on branches
node: branches can be spun around
rooted: when the branch points of the tree represent the most recent common ancestor of all the taxa in the tree
basal taxon: lineage that diverges early on (not very close to the rest of the organisms on the tree)
sister taxa: groups of organisms that share an immediate common ancestor that is not shared by any other group
What can a phylogenic tree show you?
common ancestor, sequence of ancestral organisms leading to a particular taxon
What does a phylogenic tree not show?
does not show degrees of “closeness”, cannot infer the ages of taxa or branch points
Taxonomy
organization and classification of organisms
Binomial nomenclature
Formal system of naming species
Each species name formed out of latin and has two parts
* First part of the name (generic name) identifies the genus to which the species belongs
* Second part (specific name) distinguishes the species within the genus
Monophyletic group
group in which all of the individuals are more closely related to each other than any individuals outside of that group
Polyphyletic group
lack a direct link to a common ancestor, could have analogous characteristics due to environment
Paraphyletic
includes an ancestor and only some of its descendants
Outgroup
species from an evolutionary lineage that is closely related to, but not part of group of species of interest
Ingroup
species of interest
chronogram
phylogenic tree where the branch lengths are directly related to time (always an estimate)
Maximum parsimony
an optimality criterion under which phylogenetic tree that minimizes total number of character-state changes
Horizontal gene transfer
Process through which genes are transferred from one genome to another through mechanisms such as exchange of transposable elements, plasmids, viral infection and fusions
Macroevolution
evolution on a big scale, long period of time
Microevolution
small scale evolution, only a few gene changes (ex: dogs from wolves)
Genetic variation
presence of differences in gene sequences between individual organisms of species
* allows for natural selection
4 sources of Genetic Variation
1) formation of new alleles
* can arise from mutations
* germ-line: passed onto generations, mutation in sex cells
* somatic cells: mutation not passed to generations to come
2) Altering gene # and position
* chromosomal changes (delete, disrupt, rearrange <- deletion is most harmful)
3) Rapid reproduction
* mutations quickly generate genetic variation in prokaryotes due to quick lifespan
4) Sexual reproduction
* multiple ways offspring are different from their parents and siblings (crossing over, reassortment of homologies, alleles coming from 2 parents)
Population
Group of individuals of same species that live in same area (relative) and interbreed, producing fertile offspring
must be natural (no populations that only exist in captivity)
Gene pool
All copies of every type of alleles at every locus in all members of population
Adaptive Evolution
traits that enhance survival or reproduction tend to increase in frequency over time
*ex: giraffe’s necks grew over time because the longer they were, the more fit they were (able to reach tall leaves)
Genetic Drift
in small populations, by random chance alone, it is possible for allele frequencies to change from one generation to next
*ie allele frequencies will be different if change in population number occurs (lose half of population, chance of losing allele (that was rare already) is high))
Fixation
genetic drift can lead to fixation for one allele or gene (allele is completely wiped out)
Founder effect
(type of genetic drift): small number of individuals may leave population and become founding members of new isolated population
Bottleneck effect
(type of genetic drift): a lot of parent population is wiped out and the surviving individuals have a different allele frequency
*ex: sea lions were hunted down to 30 which were only brown and white and thus those are the only existing colors today (used to have grey and black too)
Gene flow
Transfer of alleles into or out of population due to movement of fertile individuals or their gametes
Relative Fitness
contribution an individual makes to gene pool of next generation relative to contributions of other individuals
- Relative fitness = Absolute fitness / average fitness (average # of offspring)
3 Modes of Natural Selection
1) Stabilizing: individuals with middle phenotype are selected (ex: infant birth weight)
2) Disruptive: Extreme phenotypes are favored (ex: finches with 2 sizes of beaks; middle size wont be able to eat small food or break hard food)
3) Directional: Either extremes (to the right or to the left) (ex: moths; when the trees turned black, it was better to be a black moth. When things got cleaner, the curve changed again because it was no longer good to be black)
Balancing selection
preserving variation at some loci, therefore maintaining two or more phenotypic forms in population
Heterozygote advantage
If individuals who are heterozygous at particular locus have greater fitness than do both kinds of homozygous
example: sickle cell gene
Aa: Resistant to malaria and only mild sickle cell disease
AA: susceptible to malaria but no sickle cell
aa: resistant to malaria but has fatal sickle cell disease
Frequency-dependent selection
when fitness of phenotype depends on how common it is in the population
Example: warning coloration
In aposematic species (uses color to warn predators that they should not be eaten via venom, poison, etc.): predators are more likely to remember common color pattern that they have already encountered than one that is rare
Sexual Selection
process in which individuals with certain inherited characteristics are more likely than other individuals of same sex to obtain mates
Sexual dimorphism
differences in a secondary sexual characteristic between males and females of the same species (size, color, ornamentation, rituals)
Intrasexual competition
individuals of one sex, usually males, gain competitive edge by fighting with each other. Winners claim the female
Speciation
process by which one species splits into two species
Species
group of actually or potentially interbreeding natural populations that are reproductively isolated
Biological Species Concept
Uses breeding behavior as basis for demarcating species
Reproductive Isolation
existence of biological factors or barriers that impede members of two species from interbreeding and producing viable, fertile offspring
Prezygotic Isolating Mechanisms
1) Habitat Isolation
* gene flow restricted because populations occupy different habitats of same area (ex: floor snakes and tree snakes)
2) Temporal Isolation
* mate at different times (ex: hawks (day) and owls (night), or pandas (only breed once a year))
3) Behavioral Isolation
* populations develop different courtship rituals that don’t attract outside populations (ex: bird dances)
4) Mechanical Isolation
* morphological or anatomical differences (sex organs do not fit each other)
5) Gamete Isolation
* biochemical or cellular differences (sperm is unable to fertilize the egg)
Postzygotic Isolating Mechanisms
1) Reduced hybrid viability
* genes interact in ways that impair offsprings chances of survival (most hybrids do not complete development and are too weak to survive)
2) Reduced hybrid fertility
* hybrids may be sterile (ex: mules cannot interbreed)
3) Hybrid breakdown
* some hybrids survive but if they reproduce, the next generation is unable to survive (weak or sterile) (ex: ligers)
Morphological species concept
method of classifying organisms into species based on their morphology (how similar they look)
Ecological species concept
definition of species as set of organisms that is adapted to particular set of resources in environment (how an animal plays its role in the environment (ex: bees pollinating))
Allopatric speciation
physical barriers will create new species
Sympatric speciation
in the same area but still reproductively isolated. can occur if gene flow is reduced by:
a) polyploidy - extra set of chromosomes via mutation
b) habitat differentiation- subpopulation exploits habitat not used by parent population
c) sexual selection - mate choice based on male breeding coloration
Hybrid zones
region in which members of different species meet and mate, producing at least some offspring of mixed ancestry
*Reinforcement: reinforcing reproductive barriers (natural selection should strengthen prezygotic barriers to reproduction)
*Fusion: two hybrid species fuse into a single species (mechanism keeping them separate was weak)
*Stability: hybrids continue to reproduce, sometimes because hybrids survive or reproduce better than members of either parent species
Adaptive radiation
Organisms diversify rapidly from an ancestral species into multitude of new forms, particularly when change in environment makes new resources available (ex: extinction of dinosaurs)
Colonization events
Colonizers find large number of opportunities for adaptation and diversification (like the founder effect)
3 phenomena that led to adaptive radiation
1) mass extinction
2) colonization events
3) evolutionary innovations
Heterochrony
evolutionary change in rate or timing of developmental events
ex: humans/chimps: genetic mutations in humans slowed growth of jaw relative to other parts of the skull
Paedomorphosis
condition where sexually mature stage of species may retain body features that were juvenile structures in ancestral species
Homeotic genes
genes that control patterns of body formation during early embryonic development of organisms
Primates
mammals with 2 distinct features
1) grasping fingers and toes
2) binocular vision
How long ago did primates split into two groups? What are those groups
40 million years ago
Prosimians & Anthropoids
Prosimians
lemurs, tarsiers, lorises
* primitive, more reliant on smell (mark territory with scent), laterally places eyes, differences in reproductive physiology)
Anthropoids
higher primates (monkeys, apes, humans)
* bigger; bigger brain, more parental care
New world monkeys
wide range in size, diet, ecological adaptation
* almost exclusively living in trees
Hominoids
apes hominids (humans and their direct ancestors)
* orangutans, gorillas, chimpanzees
* no tail
* longer infancy period
Taxanomic rank (biological classification) ex: fox
DOMAIN (eukarya), KINGDOM (animalia), PHYLUM (chordata), CLASS (mammalia), ORDER (carnivora), FAMILY (candiae), GENUS (vulpes), SPECIES (vulpes vuples)
