mastering biology chapter 13

natural selection

* individuals with certain inherited traits are more likely to survive & reproduce than individuals without those traits
* nature chooses who survives & reproduces

stabilizing selection

natural selection that favors intermediate phenotypes

directional selection

* natural selection that favors 1 extreme phenotype
* seen in environments that change over time
* can be caused by changes in weather, climate, or food availability

disruptive selection

* natural selection that favors both extreme phenotypes
* shows phenotypes of both
* most rare

sexual selection

natural selection in which individuals with certain inherited traits are more likely to obtain mates than others

intrasexual selection

natural selection in which individuals of the same sex compete with one another for mates

intersexual selection

individuals of 1 sex are choosy in selection of their mates

balancing selection

natural selection that maintains stable frequencies of 2 or more phenotypic forms in a pop.

artificial selection

* selective breeding of organisms to promote the occurrence of desirable traits in offspring
* humans choose who survives & reproduces

inbreeding

* maintains desired traits in offspring by mating closely related individuals
* pros: can get improved organisms & no special tools/lab equipment are needed
* cons: undesireable traits from both parents may appear & disease can accumulate in population

hybridization

* 2 organisms of different but closely related species are mated with the hope of getting the best qualities of each parent in the offspring
* hybrids are almost always sterile
* does not work in unrelated genes

genetic engineering

takes DNA from 1 organism & inserts it into another organism's DNA sequence to ensure the organism will have that specific trait

speciation

formation of a new species

allopatric speciation

pop. of same species become isolated due to geographical changes

sympatric speciation

pop. of same species evolve differently until they can no longer interbreed, taking place w/o geographic isolation

evolution

* idea that living species are descendants of ancestral species that were different from present-day ones
* genetic changes in a pop. from generation to generation

convergent evolution

* species from diff. evolutionary branches coming to resemble one another
* can result from living in similar environments or natural selection favoring similar adaptations

divergent evolution

organisms with a common ancestor becoming different as time goes

common descent

theory that all modern organisms descended from a single ancestral species i.e. tree of life

evolutionary tree

branching diagram that reflects a hypothesis about evolutionary relationships among groups of organisms

adaptation

inherited character that enhances an organism’s ability to survive & reproduce in a certain environment

DNA sequences

* aligned sequences used to figure out which organisms are most closely related to one another
* shows that all species have a common ancestor i.e. DNA shared by humans, bacteria, & dinosaurs

mutation

change in the genetic information of a cell

fossil

* preserved remnant/impression of an organism that lived in the past
* shows a progression of evolution i.e. giant sloth fossils share similarity with current sloths
* ex: trace, amber, cast, mold

fossil record

highly ordered sequence in which fossils are found in layers of sedimentary rock

homology

similarity in characters resulting from shared ancestry

homologous structures

similar structures in different species due to common ancestry i.e. limbs of humans, whales, & bats

vestigial structures

* Feature of an organism that is a historical remnant of an important structure in the organism’s ancestors i.e. human appendix, snake pelvic bone
* Provides evidence of ancestry & traces the evolutionary origin of species

embryo

* unborn organism in the process of development
* can share similarity with other embryos & show structures that are not visible when the organism is fully formed i.e. gill arches

gene flow

transfer of alleles from 1 pop. to another as a result of the movement of individuals or their gametes

gene pool

all copies of every type of allele at every locus in all members of a population

relative fitness

contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals in the population

microevolution

change in a population’s gene pool over generations

genetic drift

* change in the gene pool of a population due to chance
* effects are most pronounced in small pop.

bottleneck effect

* genetic drift resulting from a drastic reduction in pop. size
* surviving pop. is no longer genetically representative of the original pop.

founder effect

* genetic drift that occurs when individuals become isolated from a larger pop.
* new gene pool is not reflective of that of the original pop.

Hardy-Weinberg equilibrium

* state in which frequencies of alleles & genotypes in a population remain constant from generation to generation
* happens only in very large populations with no gene flow between pop., no mutations, random mating, & no natural selection
* pˆ2 + 2pq + qˆ2 = 1
* p + q = 1

taxonomic system

* kingdom
* phylum
* class
* order
* family
* genus
* species

phylogeny

study of how living & extinct organisms are related to one another

phylogenetic systematics

groups species into larger categories based on evolutionary relationships

cladogram (phylogenetic tree)

diagram used to show evolutionary relations among organisms

clade

group of living & extinct species that includes a single common ancestor

node

last point at which new lineages share a common ancestor

root

common ancestor shared by all organisms in a cladogram

derived character

* trait that arose in the most recent common ancestor of a lineage
* is passed on to its descendants

symbiosis

* close, continuous association between organisms of different species
* at least 1 of the species benefits

mutualism

both members benefit

commensalism

1 member benefits & the other is neither harmed/benefited

parasitism

1 member benefits & the other is harmed

ecological succession

* natural, gradual changes in the types of species in an area
* can be primary/secondary

primary succession

* begins without soil
* starts with the arrival of living species (pioneer species)
* simple plants die, adding nutrients to the soil
* other organisms begin to move in

secondary succession

* begins in a place that already has soil & is once the home of organisms
* occurs faster
* area colonized by organisms is disturbed before being recolonizing after the disurbance

pioneer species

species that are the first to colonize barren environments i.e. bacteria, lichen, moss, fungi

climax community

relatively stable group of plants & animals that is the end result of succession

population growth

* increase in the # of individuals in a pop.
* growth = births - deaths

k-selected species

* large species that inhabit stable environments
* few offspring at each birth
* offered extended parental care
* offspring have better chance of survival, many surviving into old age

r-selected species

* inhabit disturbed environments
* many offspring at each birth
* offered little to no parental care
* offspring have a lower chance of survival

j-shaped curve

exponential growth

type II survivorship curve

organisms mostly die equally at each interval

logistic growth

* growth that decreases as resources become scarce
* levels off when carrying capacity reaches the limit

carrying capacity

number of organisms an ecosystem can support

limiting factors

constrains the size of a pop.

density dependent limiting factor

biotic factors i.e. predation, parasites, disease, competition

density independent limiting factor

* abiotic factors i.e. drought, changes in weather, natural disasters
* can occur in both small & large pop. (not dependent on pop. size)

positive feedback

drives change by moving a system in 1 direction i.e. melting of polar ice caps

negative feedback

keeps a system in balance i.e. predator prey relationships