Please enable JavaScript.
Coggle requires JavaScript to display documents.
Evolution (Ch. 23: Evolution of Populations (Natural Selection Causes…
Evolution
Ch. 23: Evolution of Populations
Genetic Variation
microevolution: evolutionary change in pops.
genetic variation: diffs. among individs. in composition of their genes
assures the continuation of evolution bc environment is always changing, and orgs. need to be equipped with the traits needed to survive and reproduce
seen in phenotype or can be internal variation
new alleles can appear from mutations, which can be passed around a pop. as recessive, and might be harmful (sickle cell)
neutral variation: mutations that have no effect on indivds.
usually, natural selection gets rid of mutations in a pop. but not if they're on recessive alleles
mutations can arise from mistakes in meiosis that would affect genes or chromosomes
Hardy-Weinberg Equation
used to test whether a pop. is evolving
population: group of individs. of same species that live in same area and interbreed, producing fertile offspring
each pop. has a gene pool: consists of all copies of every type of allele at every locus in all members of the pop.
Hardy-Weinberg equilibrium: in a pop. that ins't evolving, allele and genotype frequencies will stay constant through generations
p^2+2pq+q^2=1
p^2= homo dom
2pq= hetero
q^2= homo rec
p+q=1
Allele Frequency Changes
natural selection: based on variation, those with better traits suited to the environment produce more offspring
adaptive evolution: traits that enhance survival or reproduction tend to increase in frequency over time
some fruit flies had an allele that allowed them to resist insecticides, as time passed, this allele increased in frequency in the pop.
genetic drift: chance events can cause allele frequencies to fluctuate unpredictably from one generation to the next
effects of gene drift
founder effect: when a few individs. become isolated from main pop, the smaller group becomes a new pop. with a diff. gene pool from the main pop.
Darwin's finches
bottleneck effect: severe drop in pop. size bc of a sudden change in the environment like a fire or flood
surviving gene pool has under/over-represented alleles
sometimes humans cause this like hunting greater prairie chicken
significant in small pops. bc causes alleles to be overly disproportionate
can cause allele frequencies to change at random throughout future generations
can lead to a loss of variation within pops. bc it could eliminate alleles from that pop.
can cause harmful alleles to become fixed (reach a frequency of 100%), which threatens the pop.'s survival
gene flow: transfer of alleles into or out of a pop. (can come from another pop.) due to the movement of fertile individs. or their gametes
humans today travel a lot and mate with other races, leading to an exchange of alleles and fewer genetic diffs. between those pops.
Natural Selection Causes Adaptive Evolution
relative fitness: the contribution an individ. makes to the gene pool of next gen. compared to the other contributions of other individs.
in a given environment, certain traits can lead to greater relative fitness such as how a moth that has the most offspring has colors that conceal it the most in its environment
frequency distribution of heritable traits
directional selection: bell curve shifts to one extreme bc environmental change causes majority of pop. to be more extreme
ex. abundance of large seeds causes pop. to have more finches with large beaks
disruptive selection: conditions favor individs. at both extremes
ex. small-billed birds can crack soft seeds and large-billed birds can crack hard seeds, but birds with normal-sized beaks can't crack either
stabilizing selection: favors intermediate variants more strongly, and both extremes die off
ex. human babies who weigh 6-8lbs outlive babies who are smaller or bigger at birth
sexual selection: individs. with certain inherited traits are more likely to obtain mates
sexual dimorphism: diff. in secondary sex characteristics between males and females of same species
caused by sexual selection
include diffs. in size, color, ornamentation, and behavior
intrasexual selection:males compete for female mate, female doesn't have any say in the matter bc whoever wins is the mate
2 lions fighting over a female
intersexual selection: mate choice, females choose their mate based on the male's features
peahen chooses peacock with brighter, larger feathers
balancing selection: 2 or more phenotypes being maintained in a pop. bc selection preserves variation at some loci
frequency-dependent selection: the fitness of a phenotype depends on how common it is in the pop.
a trait can disappear if indiids. with that trait don't reproduce
heterozygote advantage: heterozygotes have better fitness than homozygotes bc their dom. allele wins out the rec. allele
if there's a harmful recessive allele, homo rec. individs. would die and reproduce less like sickle cell disease
heterozygotes have one sickle cell allele and one normal dom. allele which wins over and makes these individs. resistant against malaria
if female birds like 2 diff. colors of feathers, those traits stay in the gene pool
evolution can't make perfect orgs.
selection can only act on existing alleles and variations
evolution can only work with existing anatomy of orgs., it can't abruptly create new limbs or features
adaptations are compromises, ex. humans have 4 useful limbs but we can't run like horses
chance, natural selection, and environment affect evolution
Ch. 24: Origin of Species
Biological Species Concept
a species is a group of pops. whose members can interbreed, producing viable and fertile offspring with each other but not with other members of other groups
humans can all breed with each other, so we are one species
reproductive isolation: existence of bio factors that stop 2 species from interbreeding
block gene flow and limit formation of hybrids
prezygotic barriers block fertilization from occurring
habitat isolation
temporal isolation: diff. mating seasons
behavioral isolation: female decides she doesn't like male
mechanical isolation: 2 species are morphologically diff. enough that they can't successfully mate
gametic isolation: some sperm can't fertilize eggs of another species
postzygotic barriers lead to reproductive isolation after hybrid zygote is formed
reduced hybrid viability: hybrids are weak and don't survive
reduced hybrid fertility
hybrid breakdown: 1st gen. hybrids are viable and fertile, but 2nd gen. hybrids are feeble and sterile
biological species concept is limited
doesn't apply to orgs. that reproduce asexually like prokaryotes
gene flow still occurs between some species that are morphologically and ecologically diff.
fossils can't show reproductive isolation (sterility)
speciation: the process by which one species splits into 2 or more species
microevolution: changes over time in allele frequencies in a pop.
macroevolution: broad pattern of evolution above the species level
morpholical species concept distinguishes species by body shape
limitation: some species have members that look diff
ex. Chihuahua and St. Bernard are unlikely to mate even though they're in same species
ecological species concept: how species interact with their environment and what area they live in
How Speciation Occurs
allopatric speciation: species splits into diff. areas and becomes diff. species
ex. a rive may change paths and divide a species, so now 2 diff. species (one on each side of river)
speciation occurs when there's no more gene flow between 2 groups that were once one species
sympatric speciation: occurs in pops. that live in same area
polyploidy: extra sets of chroms. from an accident during cell division
more common in plants than in animals
autopolyploid: has more than 2 chrom. sets derived from a single species
allopolyploid: a fertile hybrid polyploid that can interbreed with other hybrid polyploids but not with either parent species
sexual selection
females choose mates with specific features and ignore those of another "species"
ex. female cichlid fish choose mates with certain colors, but when light is off, cichlids choose whoever
habitat differentiation
ex. main pop. of flies lived on hawthorn trees, but now new pop. lives on apple trees (habitat isolation)
temporal isolation bc apples and hawthorn fruit mature at diff. rates, so flies have to reproduce accordingly and now have diff. mating seasons
Hybrid Zones
region in which members of diff. species meet and mate
ex. fire-bellied and yellow-bellied toads are diff. species, but sometimes they mate with each other and produce hybrids
hybrid zones over time
hybrids become reproductively isolated from their parent species and become a new species, while parent species are still alive
reinforcement: parent species reinforce reproductive barriers, which decreases more production of hybrid offspring
so much gene flow occurs between parent species, that they start fusing into one species (hybrids)
Rate of Speciation
patterns in fossil record
punctuated equilibria: long period of no change in fossils, until sudden change (new species was abruptly created)
some species gradually change over long period of time
speciation rates
with punctuated pattern, when speciation begins, new species is formed rapidly
with gradual changes in species, speciation might span between 4,000-40 million years
Ch. 22: Darwin & Evolution
Darwinian Revolution
evolution: "descent with modification"
species change as descendants develop new traits
Darwin's influencers
Aristotle (384-322BCE) thought species did not change (they were "fixed")
scale of nature: each life form is perfect and permanent and has its own rung on the ladder
Carolus Linnaeus (1707-1778) developed binomial nomenclature (genus species)
he grouped species into general categories (genus)
Georges Cuvier (1769-1832) developed paleontology (study of fossils)
strata: layers of rock in which fossils are found
the older a fossil is, the farther down is its stratum
every new layer of stratum holds a diff, newer species of fossil
rejected the idea of evolution, and believed that species were diff. from others bc of sudden natural disasters
James Hutton (1726-1797) thought that Earth's features were created by gradual occurrences like a lake turning into a valley
Charles Lyell (1797-1875) thought that geological processes occur at slow and continuous rates, and that this has been happening since the beginning of time
Lamarck (1744-1829)
proposed ideas that were rejected by Darwin
inheritance of acquired characteristics: organism passes its modifications to its offspring
use and disuse: body parts that are used the most become larger and stronger, and those that aren't used deteriorate
Unity & Diversity of Life
adaptations: inherited characteristics that enhance survival and reproduction
Darwin discovered many finches with different-sized beaks
natural selection: individuals that have the best adaptations tend to reproduce and survive
"The Origin of Species"
"descent with modification" is what Darwin called evolution
artificial selection: humans select orgs. to breed to produce a desired trait
Darwin's observations
1) there is variability in a population's traits
2) all species produce more offspring than the environment can support; many babies fail to survive and reproduce
Darwin's inferences
1) survival of the fittest: those best adapted to their environment have more offspring
2) over generations, favorable traits will accumulate in a pop.
over time, natural selection increases the frequency of favorable adaptations in a pop.
new species can arise from environmental changes or when orgs. move to a new environment
Evidence of Evolution
homology: similarity resulting from common ancestry
characteristics can be similar but have different functions
humans and whales have the same bones, but they use their limbs for different functions
homologous structures: suggests a common ancestor
vestigial structures: remnants of features that served a function in the organism's ancestors
snakes have pelvis and leg bones, but they don't walk
evolutionary tree: diagram that reflects evolutionary relationships among groups of organisms
convergent evolution: the independent evolution of similar features in diff lineages
distantly related orgs. resemble one another bc of the similar environments they live in
sugar glider is a marsupial that lives in Australia, and flying squirrel isn't a marsupial and lives in US
analogous features: share similar function but not common ancestry
biogeography: scientific study of geographic distributions of species
endemic: found nowhere else in the world (like Galapagos finches)