Unit 7: Natural Selection (AP BIO) Flashcards

changing life forms

layers of rock where fossils are deposited

• the older strata are deposited first

geologic processes that have shaped planet = uniform over time -> Earth must be older than previously thought (a few thousand years)

proposed a mechanism for evolution based on use and disuse & inheritance of acquired characteristics

• parts of the body use extensively become larger and stronger
• those not used deteriorate

characteristics acquired in lifetime -> passed onto next generation

(flawed theory)

recognized that species evolve; organisms and environment match through this gradual evolutionary change

inheritance of acquired characteristics - wrong

an old Earth has time for evolution; a young Earth doesn't -> gave Darwin the "gift of time"

A weightlifter's child could be born with a more muscular anatomy

Darwin's voyage on the HMS Beagle

• Darwin's mechanism for evolution
• explains how adaptations arise

results in alleles being passed to the next generation in proportions different from their relative frequencies in the present generation

• heritable characteristics
• enhance an organism's ability to survive and reproduce in specific environments

• Desert foxes have large ears, which radiate heat
• Arctic foxes have small ears, which conserve body heat

members of a population often vary in their inherited phenotypic traits

• a species can produce far more offspring than environment can support
• competition is inevitable

individuals with inherited traits that are better suited to local environment = more likely to survive and reproduce

"differential reproductive success"

the reproductive success of an individual in a population

evolution -> unequal reproductive success of individuals -> accumulation of favorable traits in the population over generations

the match between organisms and their environment

natural selection may result in adaptation to these new conditions

the new environment

populations evolve

• an individual cannot change its genetic makeup, but differential reproduce success overtime can change it.

a change in the genetic makeup of a population over time

• change in allelic frequencies

process by which species are modified by humans

selective breeding for milk or meat production; development of dog breeds

• direct observations
• homology
• the fossil record
• biogeography

• populations of organisms continue to evolve in real time

• insect populations can become rapidly resistant to pesticides such as DDT
• bacterial populations become resistant to antibiotics, and viruses become resistant to other drugs

• similarity resulting from common ancestry

characteristics in related species can have an underlying similarity even though they have very different functions

anatomical signs of evolution

• forelimbs of mammals that are now used for a variety of purposes: flying in bats, swimming in whales

present and used in a common ancestor

• comparison of early stages of animal development
• reveals many anatomical homologies in embryos, not visible in the adult organism

all vertebrate embryos have a post-anal tail and pharyngeal pouches

• remnants of structures that served important functions in the organism's ancestors
• structures of marginal, if any, importance to an organism

• some snakes have remnants of pelvis and leg bones

• shared characteristics on the molecular level

• all life forms use the same genetic language of DNA and RNA
• amino acid sequences, coding for hemoglobin in primate species, shows great similarity (indicating a common ancestor)

• two species develop similarities as they adapted to similar environmental changes
• NOT because they evolved from common ancestor

explains why distantly related species can resemble one another

analogous, not homologous

• torpedo shapes of penguin, dolphin, and shark = solution to movement through aqueous environment
• sugar gliders and flying squirrels occupy similar niches in their respective habitats

"similar problems have similar solutions"

the study of fossils

• shows that evolutionary changes have occurred over time
• provide evidence of the origin of major new groups of organisms

succession of forms!

link ancient organisms to modern species

the geographic distribution of species

tend to be more closely related to each other than species in distant geographic areas

• In South America, desert animals are more closely related to local animals in other habitats than they are to desert animals of Asia

• can explain the similarity of species on continents that are distant from each other today

found at a certain geographic location and nowhere else

• Marine iguanas - found on Galápagos Islands and nowhere else

genetic variation

• having / not having attached ear lobes
• range in height

• result in genetic variation on which natural selection can act

only source of new genes and new alleles

gametes can be passed to offspring

• changes in one nucleotide base in a gene
• can have a significant impact on phenotype

sickle cell disease

• delete, disrupt, duplicate, or rearrange many loci at once
• usually harmful, but not always

• result in an expanded genome with new genes
• may accumulate mutations over generations and take on new functions

the sexual recombination of alleles that already exist in a population

shifts existing alleles and deals them at random to produce individual genotypes

• crossing over (prophase I of meiosis)
• independent assortment of chromosomes during meiosis
• fertilization

a group of Individuals of the same species that live in the same area and interbreed, producing fertile offspring

the study of how populations change genetically over time

all of the alleles at all loci in all the members of a population

two (and the individual may be heterozygous or homozygous)

all members of a population are homozygous for the same allele

• only one allele exists at that particular locus in the population

the lower the species' genetic diversity

used to describe a population that is not evolving

• states the frequencies of alleles and genes in a population's gene pool will remain constant unless acted upon by forces other than Mendelian segregation and recombination of alleles

1) no change in allelic frequency due to mutation

2) random mating

3) no natural selection

4) extremely large population size

5) no migration

provides an excellent null hypothesis (conditions are seldom met in natural populations)

• if Hardy Weinberg analysis shows change in allelic frequency, can figure out which condition isn't being met

• natural selection
• genetic drift
• gene flow

• individuals with variations that are better suited to their environment tend to survive and produce more offspring than those with variations that are less suited

organisms adapted to their environment

unpredictable fluctuation in allele frequencies from one generation to the next

• random, unadaptive change in allele frequencies

the greater the chance there is for genetic drift

• founder effect
• bottleneck effect

a few individuals become isolated from a larger population and establish a new population whose gene pool is not reflective of the source population

a mat of vegetation washes up on the shore of a Pacific island, host to a small population of lizards

• its gene pool is randomly different than that of the source population

a sudden change in the environment that drastically reduces the size of a population

• the few survivors that pass through the restrictive bottleneck may have a gene pool that no longer reflects that of the original population

• The population of California condors was reduced to nine individuals

occurs when a population gains or loses alleles by genetic additions or subtractions from the population (often by migration)

• results from the movement of fertile individuals or gametes

alleles between different populations are mixed, resulting in a reduction of genetic differences between the populations

genetic differences between populations, making them more similar

isolated populations do not experience it, tend to adapt to their unique environments and may have significant genetic differences from the ancestral population

the contribution an organism makes to the gene pool of the next-generation relative to the contributions of other members

by reproductive success

phenotype

genotype

• directional selection
• disruptive selection
• stabilizing selection

• shifts the overall makeup of the population by favoring variants that are at one extreme of the distribution

• darker mice are favored because they live among dark rocks

• favors variants at both ends of the distribution

• mice that colonize a patchy habitat made up of light and dark rocks, mice of an intermediate color are at a disadvantage

• removes extreme variants from the population and preserves intermediate types

• environment consists of intermediate color rocks, both light and dark mice selected against.

• individuals with certain inherited characteristics are more likely than other individuals to obtain mates

• a difference between the two sexes in secondary sex characteristics such as differences in size, color, ornamentation, and behavior

• diploidy
• heterozygote advantage

• because most eukaryotes are diploid, recessive alleles are hidden from selection in heterozygotes

• occurs when two individuals who are heterozygous at a certain gene locus have an advantage for survival

• In sickle cell disease, individuals homozygous for normal hemoglobin are more susceptible to malaria, whereas homozygous recessive individuals suffer from complications of sickle-cell disease. Heterozygotes benefit from some protection from malaria and do not have sickle-cell disease (mutant allele remains relatively common)

• Selection can only edit existing variations
• evolution is limited by historical constraints
• adaptations are often compromises
• chance, natural selection, and the environment interact