IB Biology HL Unit 2

Evolution

Change in heritable characteristics (gene frequencies) of a population over time

Natural Selection

Inherited variations exist in populations, organisms w/ successful variations survive and reproduce better, passing on traits

Variation

Same species have differences

• RANDOM

4 key components of natural selection

• competition

• fitness

• adaptation

• selective pressure

Fitness

ability to survive/reproduce, depends on environment

Adaptation

variations that help an organism survive

• behavioral: instinct variation

• structural: physical variation

• physiological: variation in metabolic processes

Selective pressure

• chooses which traits are beneficial or detrimental to survival

  • predation: prey and predator have different selective pressures

  • physiological: disease resistance, metabolic efficiency, antibiotic resistance

  • sexual: traits enhancing mating success selected for

    • causes sexual dimorphism

Sexual dimorphism

males and females of the same species look different

Birds of Paradise (IB example)

Males have plumage → sexual dimorphism and sexual selection

Darwin’s observations of finches in the gallapagos (IB example)

• different beak size due to adaptive radiation

Adaptive radiation

organisms diversify from ancestral species when environmental conditions open niches

Lamarck’s theory of inheritance of acquired traits

• acquired traits are passed through generations causing evolution

• traits improve and make tasks easier

• unused parts get smaller and disappear

Evidence of evolution: comparative anatomy - homologous structures

• inherited from common ancestor shared among closely related species

  • structural similarity but not necessarily function

  • divergent evolution: organisms sharing recent common ancestor develop different traits due to environmental difference

Evidence of evolution: comparative anatomy - analogous structures

• same function, no structural/ancestral relation

  • convergent evolution: species independently evolve similar traits due to similar environment

Evidence of evolution: comparative anatomy - vestigial structures

• lost their OG function over time

  • still present in DNA

  • no harm = stays

Evidence of evolution: molecular sequences

• comparing sequences between species → understand relationship

  • compare shared genes for nucleotide sequence differences

  • reliable

Evidence of evolution: Selective breeding

traits changed by human choice

Evidence of evolution: Embryology

study development of embryos to reveal similarities between species at early stages

Evidence of evolution: fossil record

• radiometric aging determines age of rocks/fossils

  • sedimentary rocks: oldest layers at bottom

  • transitional fossil: shoes intermediate stages between ancestral and current species

Mutation

Change in genetic material, usually neutral/bad

Sickle cell allele

abnormal allele of hemoglobin

hemoglobin

protein that carries oxygen in red blood cells

allele

version of gene cause by mutations

Sickle cell disease

red blood cells become stiff and sickle shaped, get stuck

Sickle cell trait

1 normal, 1 sickle hemoglobin

can give protection from malaria

Population

group of organisms of the same species living in the same area at the same time

Biological species concept

species are reproductively compatible (can interbreed and produce fertile offspring) and are reproductively isolated from other species

speciation

process of creating species

process of speciation

isolation → independent evolution → separate (even when given the chance to interbreed they won’t)

absent gene flow

allopatric speciation

occurs in different locations

• geographic isolation

Geographic isolation

physical barrier

Sympatric speciation

occurs in same location

• behavioral, temporal, or other isolation

behavioral isolation

different behavioral pattens and/or courtship isolate species

temporal isolation

breeding at different times

ecological/habitat isolation

different habitats

mechanical isolation

structural differences preventing mating

interspecific hybridization

breeding between different species

• makes sterile offspring

reduced hybrid viability

hybrids fail to properly develop

reduced hybrid fertility

hybrids are sterile

Mules (hybrid example)

odd # of chromosomes = sterile

Rate of speciation: gradualism

small changes add up to large change over time

• has transitional fossils

Rate of speciation: punctual equilibrium

stability → abrupt change 

• lack of transitional fossils

Polyploidy

multiple copies of each chromosome more than 2

Autopolyploidy

self fertilization → polyploidy

allopolyploidy

2 diff parental species → polyploidy

Knotweeds (example of polyploidy and speciation)

over 6 species as a result of polyploidy

polyploidy occurs when

error occurs in mitosis or zygote has extra copies

3 types of natural selection

• directional

• stabilizing

• disruptive

Directional selection

one extreme is favored over the other

stabilizing selection

middle is favored over both extremes

disruptive selection

both extremes are favored over middle

John Endler’s Guppies (modeling natural selection)

• dull spots help blend in, bright spots help attract mates

• 15 generations → shift in selection

• 3 regions

  • 1: dangerous predators → dull spots

  • 2: no predators → bright spots

  • when guppies from 1 are moved to 2 they develop bright spots

• exemplifies natural and sexual selection

Mechanisms of evolution (4)

• natural selection

• gene flow

• genetic drift

• genetic mutation

gene flow

genes flow into gene population when organisms move to new area

• gene pool: all genes/alleles in a population

• newcomers change gene frequencies (genetic migration)

Genetic drift

change in gene frequencies by random chance

• due to random removal/reproduction changes

• no selective pressure causing change

Genetic mutation

change in dna sequence

• mistakes made in copying genomes b/c enzymes make mistakes

Random fertilization

randomness of which sperm reaches egg making infinite combinations

Variation in asexual reproduction comes from

genetic mutation

morphological concept of species

• by Linnaeus

• classifies organisms based on physical characteristics

• issues: don’t capture full picture of different species → similar looking species and sexual dimorphism

Biological species concept issues

• addresses issues of morphological concept of species BUT

• cannot be applied to asexual reproduction (b/c bacterial conjunction)

• dividing line between two species is unclear

  • when is a species separated into two?

Karyogram

image of chromosomes

genome

all genetic info in an organism

single nucleotide polymorphism (SNP)

replacement ofa single polynucleotide with another

genome size

amount of DNA

diploid

2 copies of each chromosome

Haploid

1 copy of each chromosome

How many chromosomes do humans have?

diploid # of 46

haploid # of 23

autosomes

chromosomes not important in sex determination

• chromosomes 1-22 in humans

homologous chromosomes

chromosomes sharing same gene sequence, location, length

sex chromosomes

determine sex

• 23rd pair in humans

• female: XX, male: XY

• not homogous

Chimpanzees chromosome # → human chromosome # (IB EXAMPLE)

• chimps have 48, 2 more than humans

  • cause: chromosome fusion

chromosome fusion

chromosome 2 in humans came from fusion of 12 and 13 in chimpanzees

clade

group of organisms with common ancestor

cladograms

• made with genome sequences 

• shows relationship between species

molecular clock

estimating time from common ancestry using genetic differences

taxonomy

scientific classification and naming of organisms

Linnaeus classification system

binomial nomenclature

2 part naming system

• 1st part is the genus (1st letter capitalized)

• 2nd part (specific epithet) is the species (all lowercase)

How to abbreviate binomial nomenclature

Only the capital letter of the genus followed by a period then the specific epithet

taxon (taxa)

taxonomic unit at any level of heirchy

taxa order broad → specific

domain kingdom phylum class order family genus species

principle of parsimony

simplest answer is usually right

Woese’s 3 kingdom classification system

• based on rRNA (ribosomal RNA) sequences

• decides domain

• 3 domains: archaea, bactera, eukarya

chemoautotroph

uses chemical energy

photoautotroph

uses light for energy

heterotroph

gets energy from other organisms

autotroph

creates organic compounds from inorganic

convergent evolution

unrelated species have similar structures with similar functions because of similar environments (analogous structures)

divergent evolution

related species have similar structures but not the same functions (homologous structures)

Genetic equilibrium

all individuals of a population have the same chance at contributing to a gene pool

• disrupted by natural selection

neodarwinism

integration of natural selection and genetics

Mendel and Weismann

created genetic explanation for neodarwinism

allele frequency

proportion of an allele in a gene pool

• evolution changes allele frequencies

Hardy-Weinberg Equation

p² + 2pq + q² = 1

calculates allele frequencies

accurate predictions mean the population is in genetic equilibrium, inaccurate ones mean evolution

Assumptions of the Hardy-Weinberg Equation

• only 2 alleles

• no mutations (new alleles)

• no immigration

• no natural selection

• large population

• random mating

Figworts (IB example)

• example of how molecular sequencing is the most reliable evidence

• were originally classifies by physical features

  • molecular sequencing showed differences →reclassification

• originally over 5000 species in the figwort family

outgroup

• species most furthestly related to other species on a cladogram

derived characteristic

• characteristic that differs one species from the next

• inherited by species but different from those of ancestral species

node

• meeting point of two branches

• represents common ancestor of two related lineages

root

• beginning of the cladogram

• represents most ancient ancestor of all species on the cladogram

protista

• eukarya domain

• eukaryote that is not an animal plant or fungus

• a kingdom

• some multi cellular, some uni

• autotrophs/heterotrophs

• some asexual reproduction/sexual

• no cell wall

• flagella and Cilia for movement

• mostly aquatic environments