evolution flashcards

hypothesis

• Proposed explanation based on limited evidence

• An educated guess

• The basis of further research – can be tested

scientific theory

• Explains why

• Supported by scientific evidence, fortified by facts and repeatedly tested

• Revised with improved evidence and technological advances

• Ex) cell theory, theory of general relativity, atomic theory, theory of evolution, theory of gravity

law

• Describes what happened

• Can usually be summarized mathematically

• Ex) Newton’s second law of motion, Mendel’s laws (law of segregation of genes, law of independent assortment, law of dominance)

variation

• Variation: The differences between individuals

• The number of possible combinations of alleles that offspring can inherit from their parents results in genetic variation among individuals within a population.

mutations

• the starting points of genetic variation in populations

  • Mutations are changes in the DNA of an organism.

    • Provide new alleles in a population

    • The only source of NEW genetic variation within a species.

mutations in gametes vs. body cells

• If a mutation occurs in a somatic (body) cell, the mutation disappears from the population when the organism dies.

• If the mutation alters the DNA in a gamete, the mutation may be passed on to succeeding generations. These mutations are inherited.

biological evolution

• An inherited (heritible) change (variations) that happens within a  POPULATION (NOT INDIVIDUALS)

• Change in the ALLELE FREQUENCIES within a population

adaptation

a structure, behaviour, or a physiological process that helps an organism survive and reproduce in a particular environment 

• Another word for reproductive success is fitness

fitness

• the relative contribution (number) an organism makes to the next generation by producing offspring that are viable (will survive long enough to reproduce) 

  • An organism with many viable offspring = high fitness

  • An organism with few or no viable offspring = low fitness

connection between variation/adaptation

• An adaptations develops when a specific variation (random, heritable mutation in DNA) provides a selective advantage (genetic advantage that improves an organism’s chances of survival and reproduction)

• This advantageous variation will gradually accumulate in a population

• Change in the ALLELE FREQUENCIES within a population = evolution (micro)

structural adaptations

specific part or feature of the organism’s body 

• Fluffy feathers of an owl allow them to make their flight silent to catch their prey; or good vision of an owl 

• Mimicry & camouflage

physiological

permits an organism to perform a specific function

• Hibernation allows squirrels to survive harsh winters 

behavioural

🡪 ways an organism acts 

• Hunting strategies, migration 

mimicry

a type of structural adaptation. Harmless species physically resemble a harmful species. Predators avoid the harmless species as much as they do the harmful one.

microevolution

• Changes in the allele frequencies within a population over successive generations 

• Ex) St. Lawrence beluga whales

allele frequencies

• Allele frequencies = number of copies of an allele compared to the total number of alleles in a population

macroevolution

• The progression of biodiversity over a long period of time  

• Descent of many species from a common ancestor 

• Accumulation of many instances of microevolution

• Involves speciation (new species) and extinction

• Therefore, microevolution can lead to macroevolution (new species), but not always!

humans in the history of evolution

• if 500 sheets of paper represents the existence of time, 1/5 of one sheet represent the age of humans, and recent humans would represent only a sliver

• Humans have only been around for a very short time and so a lot of our fossil evidence came from organisms that existed way before we did

fossils - evidence for evolution

• chronological collection of life’s remains in mostly sedimentary rock layers, hard tar pits, volcanic ash, peat bogs, or amber

• Shows the history of life by showing the kinds of species that were alive in the past

• Fossils found in young layers of rock are much more similar to species alive today than fossils found in older layers of rock

• Shows the transition from species to species

• 99% of species are extinct!

• Not all organisms appear → gaps in fossil records

• Fossils of transitional species, when found, provide a lot of information for filling in these previous gaps

burgess shale

• Age: from the Cambrian period (~508 million years ago)

  • Shortly after an astonishing burst of biodiversity occurred in the ancient oceans.

• Preservation of soft-bodied animals

  • Mostly arthropods 

  • Not only the hard parts – bones, shells, teeth – but also the muscles, gills, digestive systems 

• Opportunity to observe the way the creatures lived and interacted

transitional species

• A species that has characteristics that are shared by more than one major group of organisms

• Has traits of an ancestral group as well as derived descendant group

Transition Fossils

• how intermediary links between groups of organisms are sometimes found later

• Ex) Sinosauropteryx →  first and most primitive genus of dinosaur found with fossilized impressions of primitive feathers

Archaeopteryx – “first bird” – bird-like dinosaur

Had feathers and glided, but it also had teeth, claws on it wings and a bony tail

Allowed us to find vestigial features

Earliest members of Aves (birds) developed from small-eating dinos!

comparative anatomy

The study of similarities and differences in anatomy between species.

homologous structures

• Anatomical structures found in different species that have similar structure and were derived from a common ancestor.

• May have a different function

• Ex) Vertebrates all have the same basic arrangements of bones but have different functions

• Flipper of a porpoise, wing of a bat, leg of a horse, leg of a frog and human arm

analogous structures

• Structures that have similar functions, but do NOT share a common ancestor

• Anatomically different but perform similar function 

• Probably evolved in the different species because share similar ecological units 

vestigial

Homologous characteristics of organisms that have lost all or most of their original function in a species through evolution

• Ex) In humans: tailbone, ear muscles, wisdom teeth

biochemical analysis (DNA)

Scientists can determine how closely related two organisms are by comparing DNA and proteins 

• Uses the method of DNA barcoding

• Ex) found that dogs are related to bears

• Ex) whales and dolphins are related to hooved animals

embryology

• The study of early, pre-birth stages of an organism’s development

• Embryos of closely related organism often have similar stages in development 

  • Determines evolutionary relationships between organisms

 Biogeography

The study of the distribution of organisms and ecosystems in space and through geological time

Ex) Fossil distribution of these 4 species matches the arrangements of the Earth’s land masses at the time the species were alive.

mutations

• Change that randomly occurs in the DNA of an individual that is heritable

• Only source of new alleles (genes)

Ex) Norway rats (some had a resistance to warfarin poison)

• When warfarin was applied, those resistant to the poison survived, reproduced and passed on the allele.

• This selective advantage changed the allele frequency of this characteristic 

neutral/beneficial/harmful mutations

1. NEUTRAL mutations usually occur in non-coding regions of genetic material and do not benefit or harm the organism

   • Ex. Earlobes attached vs. not attached

2. BENEFICIAL mutations are rare but the environment selects them and, therefore, alleles resulting from them ACCUMULATE over time

   • Ex. Bacteria resistant to antibiotics (beneficial for bacteria)

3.  HARMFUL mutations occur frequently, but the environment selects against them and therefore, alleles that result from them are RARE

   Ex) Cystic Fibrosis

   
   

heterozygous advantage

Inheritance is codominant so if you are heterozygous, some of your cells are normal and some are sickle. Sickle cells can’t be infected by a mosquito because it does not carry enough oxygen

natural selection

Organisms with advantageous heritable traits are selected for, survive and REPRODUCE passing their traits to their OFFSPRING

Selective pressure selects FOR or AGAINST specific traits that allow the organism to survive and reproduce VIABLE offspring!

selective pressures

• Abiotic

  • Drought

  • Flood

  • Temperature

  • Availability of sunlight

• Biotic

  • Predators/prey

  • Parasites

  • Competition

  • Invasive species

darwins conclusions

• organisms evolve over TIME

• change occurs GRADUALLY

• all organisms come from a COMMON ancestry

• species multiply and evolve into NEW species

• surviving organisms have traits ADAPTIVE to their environment and pass those characteristics on to the next generation

darwin’s finches

• Darwin observed variation of finches → Beak suited for the type of food they are eating

directional selection

• results in a shift in one extreme aspect of a trait (moves the curve in one direction) 

• Taller giraffes are selected for, but short giraffes are selected against 

• Large brains in humans

• Long trunks and large size in elephants

• Reduced size of salmon due to overfishing

disruptive selection

•  When natural selection selects for the extreme phenotypes and acts to remove the most common characteristics.  

• The extremes may become separate species. 

• Ground finches with medium-sized beaks almost became extinct during an extended drought in the Galapagos Islands because the bushes have only hard or soft seeds

  Left separate populations with large beaks and small beaks
  

stabilizing selection

• Favours the intermediate phenotype

• Selects against the characteristics that differ from the most common (extremes)

• Human birth weight has undergone stabilizing selection

• Babies of low weight lose heat more quickly and get ill from infectious diseases more easily

• Babies of large body weight are more difficult to deliver through the pelvis

• Infants of a more medium weight (~7 lbs) have the greatest survival

non-random mating - inbreeding

• when closely related individuals breed together

• Individuals tend to mate with those who live nearer to them, than with more distant members of the same population.  Members that are closer together are more likely to be more closely related 

• share similar genotypes so the frequency of the homozygous genotype increases

• harmful recessive alleles are more frequent, therefore more likely to be expressed

non-random mating - preferred phenotypes

• Selecting a mate based on physical and behavioural traits (phenotypes)

1. Assortative Mating: When individuals mate with partners that are like themselves in certain characteristics 

ex) jumping spider - larger females are better equipped to resist male courtship attempts, and only the largest males are able to mate with them.

2. Disassortative Mating: phenotypically dissimilar organisms mate together

inbreeding/preferred phenotypes

• With inbreeding and preferred phenotypes, does NOT alter allele frequencies in a population

• However, it will increase the number of expected homozygous individuals. 

Therefore, it doesn’t cause microevolution by itself, but contributes to the mechanism of natural selection

non-random mating - sexual selection

• Certain characteristics (physical and behavioural traits) are actively sought out by ONE sex (usually the female)

SEXUAL DIMORPHISM

• a marked difference between males and females

Sexual Selection vs Natural Selection

• Both focus on increasing fitness: the ability of an organism to pass on its genetic material to its offspring

• While natural selection focuses both on survival and reproductive success, sexual selection doesn’t necessarily focus on an organism surviving longer, just its ability to pass on its traits. 

genetic drift

• Change in gene or allele frequencies in SMALL populations

• Alleles can be lost RANDOM (by CHANCE) from the population, causing dramatic changes in genetic makeup of the population

• Can result in alleles disappearing completely or becoming very common

• The smaller the sample, the greater uncertainty of your results 

gen. drift - bottleneck effect

• Large, TEMPORARY REDUCTION in the population that may result in significant genetic drift

  • By chance alone

  • A severe environmental stress (disease, starvation, natural disasters) nearly wipes out a population

  • Some alleles may be lost forever because only a small number of individuals survive and reproduce (all done randomly)

• Ex: 30 000 northern elephant seals living today are all descendants from approximately 20 individuals (hunting in 1890s)

gen. drift - founder effect

By chance, a small number of dispersed individuals establish a new population (founders) at a distance from the original population

• Causes a limited number of alleles to be present (loss of genetic diversity)

•  If the founders have rare alleles, then rare alleles will increase in frequency

•  Occurs frequently on islands

gene flow

• Movement (flow) of ALLELES from one population to another by movement of individuals

• Needs to have a migration of a fertile individual to a new population, or the transfer of gametes, between populations 

• Alters the ALLELE FREQUENCY

• Increases genetic diversity of the population

• Ex. Prairie Dogs or Lions - developing males leave to form new colonies/prides with genetically unrelated females

non-random mating - artificial selection

• The differential reproduction of genotypes caused by HUMAN INTERVENTION (e.g., breeding dogs, crops).

• Done to achieve a desired CHARACTERISTIC in the offspring

biological species concept

Modern definition of species focuses on genetics and biochemistry

• Population where individuals are able to interbreed to produce viable offspring

• Populations that can reproduce will share a gene pool and will slowly become reproductively isolated from other such groups

ex: In zoos, lions and tigers can mate and produce fertile offspring

• But naturally they live in separate areas, therefore won't interact and therefore will not interbreed = different species

how does speciation happen?

In order for speciation to happen, you need a mechanism of evolution and isolation. 

There are 2 Modes of Speciation:

1)  Allopatric speciation

2)  Sympatric speciation

allopatric speciation

• Most new species form when a single species is separated into two geographically isolated populations by geographical barrier 

• Physical separation prevents the exchange of genetic information.  

• Allele changes within each population eventually cause the gene pool of the populations to be so distinct that they would not be able to interbreed when re-introduced

sympatric speciation

• individuals within a population become genetically isolated from the larger population without geographic isolation 

• A population of a species within a single geographical region splits into separate gene pools and forms separate species.

can happen by:

• Non-random mating (preferred phenotypes)

• Different selective pressures (niches!) (at either end could alter the alleles of the population)

Other reproductive isolating mechanisms

speciation

the formation of new species from existing species

reproductive isolating mechanism

• any behavioral, structural or biochemical trait that prevents individuals of different species from reproducing successfully

prezygotic isolating

Isolating mechanisms that prevent MATING or FERTILIZATION

Ecological Isolation

• Species that occupy separate habitats or separate niches of the same habitat do not meet to mate

• Ex) mountain bluebird (Sialia currucoides) lives at high elevations, while the eastern bluebird (Sialia sialis) prefers lower elevations and does not encounter the mountain species

Temporal Isolation

• Temporal conditions refer to time of day, seasons or different years

• Different species mate at different times

• Ex) geographic ranges of western spotted skunk and eastern spotted skunk do overlap 

  • do not interbreed because the former mates in late summer and the latter in late winter 

Behavioral isolation

• The courtship and mating cues for attracting a mate are very specific for each species.

• Distinctive mating rituals in one species will not be recognized by another.

Mechanical isolation

• Structural differences in reproductive organs prevent copulation (the key does not fit the lock)

• Ex) Bush babies (small arboreal primates) are divided into several species based on distinctly shaped genitalia 

Gametic isolation

• Prevents fertilization at the molecular level

• Egg and sperm fail to fuse

  • female immune system recognizes sperm as foreign and attacks it

  • the sperm or pollen may not be adapted to the environment of the female reproductive tract 

Ex: many marine animals release sperm and eggs into the water. The sperm recognize eggs of their own species through chemical markers on the surface of the eggs.

postzygotic isolating

Isolating mechanisms that prevents VIABLE and FERTILE offspring 

In some cases, mating and fertilization between different, but related, species can occur.

However, if the offspring are not viable and fertile, then the two species continue to be considered as different.

Zygotic Mortality

• Fertilized zygotes die before birth

• Chromosomes are not compatible

• Ex) sheeps and goats can mate but the zygote is not viable 

Hybrid Inviability

• The embryo is born alive, but the hybrid is weak, experiences reduced survival and does not survive to reproduce

• Ex) lions and leopards produce hybrids with short lifespans that die before maturity

Hybrid Infertility

• Hybrids do develop normally and reach sexual maturity, but are sterile (do not produce viable gametes)

• Ex) mules result from mating of a horse and a donkey

  • has characteristics of both species, but is sterile and cannot breed

Hybrid Breakdown

Hybrids develop and produce offspring. However the F1 generation produce sterile F2 generation.

Ex. In the cotton species, hybrids between upland cotton and pima cotton can produce fertile first-generation plants. However, the second generation of hybrids often suffer from reduced viability/fertility 

pattens in macroevolution

Macroevolution refers to large-scale evolutionary patterns that occur over long periods of time

adaptative radiation

• Rapid evolution of a single species into MANY new species

• Driving force: filling a variety of new or formerly empty ecological niches 

• Usually occurs when a variety of new RESOURCES become available

divergent evolution

• species that were once similar to an ancestral species, diverge or become increasingly distinct 

Ex: Ontario has 20 species of closely related rodents, evolved from a  common ancestor

• Include red squirrels, chipmunks, porcupines, and beavers

• Unique characteristics of each have been selected for by the environment and minimizes competition

• Groups continue to evolve to fill available ecological niches

convergent evolution

• similar traits arise because different species have adapted to similar environmental conditions

  Ex: Sharks and dolphins have similar streamlined bodies

• Each is adapted for life as a high-speed carnivore

• Natural selection favoured same body shape

• Not closely related: sharks are cartilaginous fish while dolphins are mammals 
  

parallel evolution

Come from a common ancestor, but respond to similar environmental pressures, so they evolve similar traits

-ex: a resemblance between Australian marsupial mammals and placental mammals seen elsewhere.

coevolution

• One species evolves in response to the evolution of another species

Most obvious in symbiotic relationship

Ex: Yucca moths and Yucca flowers

• Yucca flowers are a certain shape so only that tiny moth can pollinate them. The moths lay their eggs in the yucca flowers and the larvae (caterpillars) live in the developing ovary and eat yucca seeds.

the speed of evolutionary change

• At the level of individual species, some evolutionary changes can be quite sudden.  

• Ex) a single mutation causing polyploidy in plants can give rise to a new species.  

• Alternatively, other changes such as the evolution of the giraffe's long neck, have occurred gradually over a period of millions of years.  

gradualism

• Based on ideas from James Hutton and Charles Lyell

• Evolutionary change is slow, gradual, and constant

• Over long periods of time, small changes accumulate resulting in dramatically different organisms

• Evidence: fossils and transitional species

Ex: The ancestors of the horse include many intermediate forms between small four-toed mammals and the present day single-toed horse.

punctuated equilibrium

• Based on the ideas of Stephen Jay Gould and Niles Eldredge

• A theory that attributes most evolutionary changes to relatively rapid spurts of change followed by long periods of little or no change

• Favourable mutations or sudden changes in environment cause selection pressures to increase

• May be too rapid to be shown in fossil record

which is right?

• Both! 

• Research shows that species with a shorter evolution evolved mostly by punctuated equilibrium, and those with a longer evolution evolved mostly by gradualism

hardy-weinberg equilibrium principle

• The principle that states that a population's allele and genotype frequencies are CONSTANT unless there is some sort of evolutionary force (mechanism) acting upon it

• Specifies the conditions under which there would be NO change in the genotype and allele frequencies from generation to generation.  This means no evolution!

hardy weinberg conditions

1. Large population size.

2. Random mating: females cannot select a male with a particular genotype or vice versa

3. No mutations: alleles in the gene pool cannot change

4. No gene flow: no exchange of genes between populations (no migration)

5. No natural selection. No genotype can have a reproductive advantage over another

hardy weinberg and microevolution

• It provides you with a baseline to compare to

• If we measure the frequencies of ALLELES and genotypes in a population and see that over time, the frequencies have changed, we can determine that the population is undergoing MICROEVOLUTION 

• Remember changes in frequencies means there is genetic variability. 

Equation for Frequencies of Alleles

• p = the frequency of the dominant allele

• q =the frequency of the recessive allele.

• And so p + q = 1

genotype frequencies

• Figure out how many genotypes there will be in the population → 400 mice = 400 genotypes

• Number of mice BB/ total number of mice

207/400=0.52  Homozygous dominant

• Number of mice Bb/ total mice

146/400=0.36 Heterozygous

• Number of mice bb/ total number of mice

47/400=0.12 Homozygous recessive 

(sum equals 1)

allele frequencies

Calculate the Allele Frequencies

• Calculate the total number of alleles in the population

• Each mouse has 2 fur colour alleles so there are:

  • 400 x 2 = 800 alleles in the population

Let’s calculate the frequency of the B Allele, for example

• Each BB mouse has 2 B alleles so they contribute:

  •  207x2 = 414 B alleles

• Each Bb has 1B allele so they contribute:

  •  146x1= 146 B alleles

• There are 414 + 146 = 560 B alleles in the population

Frequency of B allele:  p: 560/800 = 0.70

how to determine if microevolution occured?

• Allele frequencies are usually used as the determining values when deciding on whether or not evolution has occurred.

• They are usually studied over many years, and a trend is established that will help determine whether or not evolution has occurred.
  

• If data is significantly different from the original set.