IB HL BIO YR 1 UNIT TWO

evolution

change in the heritable characteristics (aka gene frequencies) of a population over time

fact: change has occurred

theory: how and why the change has occurred

comparative anatomy

study of similarities and differences between living things

homologous structures

structures inherited from common ancestor

shared among closely related species

can have similar or different functions

ex: mammal forelimbs

divergent evolution

organisms that share a recent common ancestor develop different traits due to their different environments

underlying “blueprint” for creating many structures is the same, creating homologous structures

analogous structures

similar functions

arent structurally related

dont show common descent

due to convergent evolution

ex: wings of insects and bats/birds

convergent evolution

organisms occupying similar roles and exhibiting similar traits

embryology

study of how organisms develop before birth/hatching

fossil

preserved remains or traces of ancient organisms

visual evidence of change over time

transitional fossils

organisms “in between” two species

law of superposition

older layers of earth on bottom, younger layers on top

radiometric dating

analyzing radioactive compounds in materials to determine a more exact age

ex: carbon dating

molecular evidence (for evolution)

closely related organisms have more similar DNA sequences and more similar amino acid sequence of shared proteins

molecular clock

measures time from changes in DNA

number of differences increase over time

hypothesis: DNA and protein sequences evolve at a rate consistent over time and consistent among different organisms

selective breeding

humans carefully controlling the breeding of certain plants and animals

resulting organisms show drastic differences compares to wild counterparts (evidence for evolution)

vestigal structures

inherited structures that have lost much of their original functions

stick around because theyre coded in DNA

ex: whales’/dolphins’ pelvic bones

biodiversity

diversity of life on earth

variety of living organisms (plants, animals, & microorganisms)

contains genetic/species/ecosystem diversity

comparing biodiversity:

• different geological time periods have different biodiversity levels

• evidence: fossils (fossil record = incomplete)

• current time period = more diverse than past

genetic variation

differences in genomes among individuals of the same species

created randomly without a goal

essential for natural selection

fundamental aspect of life

genetic mutation

mechanism of evolution

any change in the DNA sequence of an organism

errors in copying the genetic information during DNA replication

results in alleles or other forms of a gene

most are neutral but can be harmful or beneficial

selection pressures

factors that lead to difference in survival or reproduction

causes a change in genetic composition of a population

density-dependent factors

affect the size of the population

depend on the density or the population in a given area (availability of food, finding mates, presence of predators, etc)

biological fitness

ability of an organism to survive and reproduce, pass on genetic material to offspring

determined by environment, survival value, reproductive potential

intraspecific competition

individuals of the same species compete with each other for resources

interspecific competition

individuals of different species compete with each other for resources

sexual selection

focused on finding mate and reproducing

intrasexual selection

males competing for mate, females competing for mate

intersexual selection

individuals of one sex (often female) choosing an individual of the opposite sex as a mate

gene pool

sum total of all the alleles of all the genes present in a population

indicator of the genetic variation that exists in a population

large gene pool indicates extensive genetic variation, greater ability to adjust and adapt

genetic drift

mechanism of evolution

change in allele frequencies in the gene pool of a population

due to random events

greater impact if populations are small/geographically isolated

can occur as the bottleneck effect or the founder effect

cant be caused by selective pressures (if so, then it would be natural selection)

allele

different versions of genes

gene pool

all of the genes and alleles within a population

gene flow

mechanism of evolution

aka genetic migration

occurs when organisms from one population move to a new area, genes “flow” into new population’s gene pool

gene flow in humans increased as travel increased

natural selection

inherited variations exist in populations and organisms with successful variations will better survive, reproduce, and pass their variations to next generation

mechanism of evolution

variation

same species, some differences

some variations are not inherited (natural selection only works on inherited variations)

random

descent with modification

sexual reproduction, offspring having variations from parents and from each other

inherit (descend) from parents (with some modifications or variations)

common descent

all living things are related

share a common ancestor

adaptation

noun: any variation that helps survival

process: populations change so there is a higher percentage of organisms with favorable traits (adaptations, because adaptations allow for more reproduction)

only works if favorable traits are inherited

more adaptations leads to higher fitness and more reproduction

structural adaptations

variations in body of organisms

ex: color, shape, patterns, etc

mimicry, camouflage

behavioral adaptations

variations in instincts

ex: fight or flight, mating behaviors, food retrieval methods, etc

physiological adaptations

variations in metabolic processes

common in bacteria, insects, and plants

ex: antibiotic/pesticide resistance

selective pressure

choose what traits are beneficial/detrimental

predation

traits in prey that cause them to be selected against

traits in predators that cause them to be selected for

physiological selective pressures

disease/antibiotic resistance

metabolic efficiency

sexual selective pressures

traits that increase mating success (help with direct competition and attracting a mate)

results in sexual dimorphism

sexual dimorphism

differences between sexes in secondary sex characteristics

directional selection

one extreme is favored over the others

stabilizing selection

the middle is favored over both extremes

disruptive selection

both extremes are favored over the middle

binomial distribution

mechanisms of evolution

natural selection

gene flow

genetic drift

genetic mutation

bottleneck effect

random natural events such as earthquakes or tsunamis can lead to sudden decreases in populations

new population might not represent genetic diversity of original population

founder effect

small subset of population breaks away to colonize new area

may not be exact genetic representation of the original population

neo-darwinism

phenotype is largely a product of the genotype

natural selection increases frequency of beneficial alleles

genetic drift and gene flow can also bring changes in gene frequencies

mutation

ultimate source of genetic variation

stabilizing selection

favors average individuals with intermediate forms of the trait

eliminates the extremes

results in loss of genetic diversity

directional selection

favors one extreme form of the trait over all other forms

most seen when environment changes

disruptive selection

both extreme forms of the trait are favored over the intermediate forms

hardy-weinberg principle

in a stable population, frequency of alleles would remain constant generation after generation

p²+2pq+q²=1

equation helps calculate the genotype frequencies of homozygous dominant, heterozygous individuals, and homozygous recessive individuals

• Conditions:

  • No mutations

  • Random mating

  • No natural selection

  • No genes should enter or leave population

  • Large population

artificial selection

similar to natural selection

perpetuated by humans

humans select organisms with desirable traits

Molecular phylogeny

can determine how closely two species are related at a molecular level

more similar genes/proteins indicate more closely related

species

a group of potentially interbreeding populations

defined by reproductive compatibility

similar organisms can mate and produce viable and fertile offspring

Speciation

process by which new species arise

splitting of one ancestral species into two or more descendant species that are different and can not interbreed

creates new gene pool

reproductive isolation

all barriers that prevent populations of the same species from interbreeding and/or producing fertile offspring

geographic isolation

reproductive isolation due to geographical barriers

ex: river, dam, road, large distance between populations, etc

allopatric speciation

nothing but geographical isolation

population split into two and evolve separately

sympatric speciation

new species is formed in the same location

due to isolating mechanisms, behavioral/temporal isolation

temporal isolation

differences in the timing of the reproductive cycle (mating seasons, gamete production, etc)

behavioral isolation

differences in mating rituals (courtship dances, mating calls, etc)

prezygotic barriers

barriers that prevent formation of the zygote, prevent mating

postzygotic barriers

barriers after zygote is formed, after fertilization

inviability, sterility, etc

adaptive radiation

rapid evolution of an ancestral species in different lines to utilize the avaliable ecological niches/jobs

hybridization

interbreeding between two species that leads to a new species

new species often reproductively isolated from parent species

more common in plants

pre/postzygotic barriers exist

polyploidy

caused by non-disjunction of chromosomes during cell division (mitosis or meiosis)

caused by a diploid cell or organism acquires one or more additional sets of chromosomes

allopolyploidy

special case of polyploidy

hybrid that has multiple chromosome sets that are derived from the different parental species

can be considered sympatric speciation

morphological characteristics

physical characteristics

species

class of organisms

classified by shared morphological characteristics (Linnaeus created this system)

tend to look more similar to each other

named using both genus and species names (genus comes first, species is all lowercase, ex: Homo sapiens)

different species sharing a genus have some common characteristics

sexual dimorphism

males and females have very different characteristics

chromosome

allow DNA to be accurately copied during cell division

each species has a set number of chromosomes, common to all members of species

within nucleus of cells, only eukaryotes

number of chromosomes is a shared trait among species

karyotyping

involves isolating condensed chromosomes taken from actively dividing cells

individual chromosomes are stained to highlight banding patters

shown in a karyogram

karyotype can determine sex

genome

stores all genetic information of an organism

single-nucleotide polymorphisms (SNPs)

occurs when a single nucleotide is replaced with another

causes variation and diversity

genome size

amount of DNA in a haploid cell

different species’ genomes vary in size and sequence

not directly correlated to either organism size or complexity

exceptions to the biological species concept

when two species have same number of chromosomes so hybrid would have an equal amount of pairs

horizontal gene transfer cases variation in asexually reproducing organisms (can be organisms of different species)

dichotomous key

tool used in fieldwork to aid in the identification of organisms

composed of binomial questions/statements based on physical characteristics (ex: fur or no fur, antlers or no antlers, flat antlers or round antlers)

DNA barcoding

unknown specimen/environmental sample (typically water or soil) is collected, DNA is extracted

identified specific DNA sequences

creates a unique “barcode” which is compared to a catalog of other barcodes

helps measure biodiversity

classification

sorting and organizing of things or ideas into groups or categories based on a set of criteria

developed mainly by Carl Linnaeus

hierarchy of taxonomy

• domain

• kingdom

• phylum

• class

• order

• family

• genus

• species

cladistics

—

molecular evidence

provide the most unbiased evidence that two species belong to the same clade

cladistic analysis

technique in evolutionary biology

based on the idea that shared genetics or traits that have been passed down from a common ancestor are what identify a clade

compare base/amino acid sequences of several organisms within species

clade

group of species with a single common ancestor and a set of common traits/characteristics

must include all species descended from specific common ancestor

cant include any species that dont share common ancestor

hierarchical and can be subdivided into smaller groupings

calibration point

in molecular clock analysis

period of time in which the precise moment that two species diverged is known

caldograms

used to compare traits of various organisms and explore evolutionary links

Kingdom eubacteria

cell type: prokaryote

cell number: unicellular

mode(s) of nutrition: photosynthesis or other organisms

reproduction: asexual

cell wall: made of peptidoglycan

motility: yes, if flagella or cilia

environment: everywhere, in/on other organisms

example: E. coli

kingdom archaebacteria

cell type: prokaryote

cell number: unicellular

mode(s) of nutrition: chemosynthetic or other organisms

reproduction: asexual

cell wall: yes, not made of peptidoglycan

motility: yes, if flagella

environment: extremophile

example: colors in morning glory pools (Yellowstone)

Kingdom anamalia

cell type: eukaryotes

cell number: multicellular

mode(s) of nutrition: internal digestion

reproduction: mostly sexual

cell wall: no cell wall

motility: various ways

environment: aquatic and terrestrial

example: zebra

kingdom plantae

cell type: eukaryote

cell number: multicellular

mode(s) of nutrition: photosynthesis

reproduction: mostly sexual

cell wall: cellulose

motility: not motile

environment: aquatic and terrestrial

example: daisy

kingdom fungi

cell type: eukaryote

cell number: mostly multicellular

mode(s) of nutrition: external digestion

reproduction: mostly sexual

cell wall: chitin

motility: not motile

environment: terrestrial

example: mushrooms

kingdom protista

cell type: eukaryote

cell number: mostly unicellular

mode(s) of nutrition: mostly autotrophic

reproduction: mostly asexual

cell wall: sometimes

motility: flagella or cilia

environment: mostly aquatic

example: algae

morphological species concept

species are categorized based on shared morphological (physical) characteristics

does not capture the full picture

sex chromosomes

not homologous

play major role in sex determination

23rd pair in humans

XX (female) or XY (male)

biological species concept

defines a species taxon as a group of organisms that can successfully interbreed and produce fertile offspring

addresses two issues with morph. species concept

issues:

• cant apply to asexual reproduction

• horizontal transfer of DNA

• hard to determine exact point of speciation in eukaryotes