Evolution-
genetic change in a
line of descent over the generations`
Microevolution-
how populations of organisms change from generation to generation and how new species originate
Macroevolution-
patterns of changes in groups of related
species over broad periods of time- determine phylogeny, or evolutionary relationships among groups of
species–how different species are related
Jean-Baptiste Lamarck–theories
Use and disuse, Inheritance of acquired characteristics, Natural transformation of species
Natural transformation of species-
because of the two above,
each generation of a species is transformed into a slightly different
more complex form
Ex- giraffe developed long neck from
stretched over time bc of necessity and this trait was passed to offspring
Inheritance of acquired characteristics
features that are
acquired during the lifetime of an organism can be passed on to offspring
Use and disuse
body parts of organisms develop more when used more, and unused parts weaken
Charles Darwin–explanation
Because of strong check on populations because of limited food
supply, inherited variations that are favorable to survival will be preserved, others eliminated. (Adaptations.) Natural Selection.
Ex- Galapagos finches- 13 different species all descended from
one single species, but because of the different environment on each island, different
traits selected for, different species evolved
Adaptations
evolutionary modification that improves chances of survival in specific environment
Natural Selection definition
better adapted organisms are more likely to survive, therefore population changes over time
Charles Darwin–aspects
Variation, Overproduction, Limits on population growth, Differential reproductive success,
Variation
individuals of a population exhibit variations,
some of which improve chances of survival and others which do not
Overproduction
every generation of a species has the
capacity to produce more offspring than can survive
Limits on population growth
struggle for existence
between individuals of a species because of limited resources
Differential reproductive success-
individuals that are
best adapted to the environment (contain most favorable
traits) are more likely to survive and reproduce,
therefore their traits will pass on and others will die off
Modern synthesis-
combines Darwin’s theory and Mendel’s theory to explain how these traits are passed on
Explains that variation is caused by mutations
Paleontology
studies fossils-remains or traces left in sedimentary rock by previously existing organisms.
Oldest layer at the bottom, upper layers are successively younger- allows scientists to place events recorded in rocks in their correct sequence.
Evidence of human life begins 100k years ago
halflife
halflife--amount of time it takes half of substance to decay after 2 halflives, 25% will be left. after 3, 12.5,
Comparative anatomy-
in comparing structures from one organism to the next, scientists can discover how closely related they are
Homologous features/ homology- (+ex)
features that are derived from the same structure in a common ancestor
Ex- human arm, cat forelimb, whale front flipper, and a
bat wing all have a similar arrangement of bones, muscles, and nerves,
even though they are all used for different types of locomotion
Homoplastic features (analagous)/ homoplasy-
structurally
similar features that are not homologous but have similar functions that evolved independently in distantly related organisms
can lead to convergent evolution
Ex- wings of insects and birds evolved in order to function in flight, but each evolved from different ancestors.
Convergent evolution + ex
independent evolution of similar structures in distantly related organisms
Ex- aardvarks, anteaters, and pangolins all resemble one
another in lifestyle and structural features. All have strong, sharp claws, elongated snouts, long, sticky tongues, but each evolved from a different order
Vestigial structures- + ex
organs that are nonfunctional or
undersized. These are remnants of more developed structures that were functional in ancestral organisms
Ex- in humans, the coccyx (fused tailbones), wisdom teeth, muscles that move our ears. (Usually not eliminated entirely)
Biogeography-
study of past and present geographic distribution of
organisms, which affects their evolution. Unrelated species can
therefore look alike when found in similar environments
can occupy different niches but if they live in the same habitat
placental v marsupial
humans–placental–placenta forms, organ of exchange between
mother and baby, meaning all development happens in utero in amniotic sac
marsupial–give birth to immature baby which crawls out and up into the pouch, filled with tissue
Embryology + ex
“Ontogeny recapitulates phylogeny”- there are similar
stages in development among related species (ontogeny). This helps
establish evolutionary relationships
recapitulates–teaches
phylogeny–relationships
gill slits and tails are found in fish, chicken, pig, human embryos
Molecular biology-
studies nucleotides and amino acid sequences of
DNA and proteins from different species. Closely related species
share higher % of sequences than species distantly related
more than 98% of nucleotide sequence in
humans and chimpanzees are identical
Stabilizing selection:
ex
individuals with extreme or unusual traits are eliminated
while individuals with the most common traits are best adapted
Ex- larvae of certain fly bore into a plant and are enclosed in a
tumor until they metamorphose into adults. Large tumors, or
galls, are easily preyed on by woodpeckers, while small galls
are preyed on by wasps. Therefore, flies that form intermediate galls
are best selected for
Directional selection:
ex
Favors traits that are at one extreme while traits at the opposite extreme are selected against
Ex- insecticide resistance- the few insects that contain
resistance to an insecticide will survive and produce offspring
after several generations, population will consist of nearly all insectide-resistant
Ex- peppered moth/ industrial melanism- before the industrial
revolution, light-colored moths best camouflaged with the
lichens covering the trees, while the dark colored moth was
rarely found since it was easily preyed upon. After the
industrial revolution, the lichens were killed, exposing the dark
bark below. Therefore, the dark colored moths was now better
camouflaged and it increased in frequency
Disruptive selection: + ex
Environment favors extreme or unusual traits while selecting against intermediate traits
Ex- weeds exist in very tall forms in the wild because they can
better obtain sunlight. However, in lawns, only short weeds exist bc these
escape mowing
middle ones=no selective
advantage
Sexual selection:
Traits that allow males to mate with a large amount of females
and maximize the quantity of offspring produced have a selective advantage and are passed on to offspring (male competiton)
Females put a greater investment of energy into producing
offspring, so they choose superior males
leads to sexual dimorphism
Male competition
allows for mating opportunities to the strongest males, leading to the evolution of antlers and horns
Female choice
females choose traits or behaviors that
are attractive, like colorful feathers or elaborate mating behavior
sexual dimorphism-
differences in appearances of males and females within a species
Artificial selection + ex
Directional selection carried out by humans when breeding plants or animals that possess desirable traits
Ex- certain breeds of dogs; brussel sprouts, cauliflower,
and broccoli all come from one species of wild mustard
Gene flow
introduction or removal of alleles from a population when emigration or immigration occur
Genetic drift
random change in allele frequencies over generations brought about
by chance. When populations are small, genetic drift has a greater effect and can influence evolution. 2 types.
Types of genetic drift
bottleneck + founder effect
bottleneck
when very few individuals rebuild a population after a severe reduction in population size
Founder effect + ex
type of bottleneck in which a few individuals leave a population and establish a new one somewhere else
Ex–one of the founders of the Amish possessed allele for polydactyly and this trait now occurs at a large scale
nonrandom mating
individuals choose mates based on their particular traits which could be similar or different from their own
sexual selection
females choose males based on attractive appearances or abilities
inbreeding
nonrandom mating among closely related relatives, which have many alleles in common. lowers fitness (ability to form surviving offspring) of population
Mutations–>Variations
can invent new alleles that never previously existed
Sexual reproduction
allows for genetic recombination: Crossing over during prophase I, Independent assortment during metaphase I, Random joining of alleles during fertilization
Diploidy
more variation is maintained in a population because of the presence of two copies of every gene
the recessive allele can be hidden but passed on
Outbreeding
mating with unrelated partners creates new allele combinations
Balanced polymorphism
maintenance of different phenotypes in a population
Heterozygote advantage
Individuals that are heterozygous have a greater selective advantage than either homozygous condition. Therefore-both alleles and all 3 phenotypes maintained in population
sickle cell anemia
Heterozygote advantage
Ex- sickle cell anemia- those that are homozygous for sickle cell (Hb S Hb S ) die before puberty. Those that have Hb A Hb A are normal. Those that are heterozygous- Hb A Hb S are generally healthy but have reduced oxygen- carrying capabilities during exercise. However- in Africa 14% of population are heterozygous bc of a selective advantage making them resistant to malaria
Frequency dependent selection (minority advantage)- + ex
when least common phenotypes have a selective advantage. However, they soon increase in frequency and lose their selective advantage
phenotypes therefore alternate between the two
Ex- predators form a “common representation” of their prey in order to optimize its search. Prey that rare escapes until it’s no longer rare
Neutral variation-
variation that does not have a selective advantage or disadvantage
Genetic equilibrium
when frequency of alleles in a population remains constant from generation to generation
In order for equilibrium to occur, the following conditions must be true
random mating and no genetic drift, gene flow, mutations or natural selection
P
frequency of dominant allele
Q
frequency of recessive allele
p2
frequency of homozygous dominant individuals
q2
frequency of homozygous recessive individuals
pq + qp = 2pq
frequency of heterozygous individuals
hardy-weinberg equations
p + q = 1 (sum of all alleles = 100%)
p 2 + 2pq + q 2 = 1 (sum of all individuals = 100%)
if the population is at equilibrium, what will happen to frequencies?
frequencies will be the same in every generation
In most natural populations, are the conditions observed?
not obeyed
What does it mean when the genotypes and phenotypes are in different proportions?
one of the conditions isn’t being met
