evolution

Condition for Hardy-Weinberg Equilibrium

1. There is no natural selection: all individuals have an equal chance of surviving 

2. There is no mutation: no new genotypes will arise 

3. There is no migration: no new alleles/genotypes will get added to the population 

4. There is a large population: there are many copies of every allele/genotype

5. Random mating: every individual has an equal chance of mating

How do we know there are no naturally existing populations in the Hardy-Weinberg equilibrium?

• Because natural selection, mutations, migration, small populations and non-random mating exist naturally in all populations.aturally

Why do we bother learning this if it is unrealistic/unrepresentative of existing populations/what is this good for?

• In population genetics it provides us with a null hypothesis (a baseline of what a population’s genetic makeup should look like if it is not evolving

• When expected frequencies in a population don’t match H-W values, that is evidence that evolutionary forces are acting upon it 

What is evolution?

• The change in heritable characteristics of biological populations over successive generations

Lamarck’s Theory

•  believed that organisms could change during their lifetime, then pass those acquired changes to offspring (from slide: excessive use of  body parts improves them & disuse worsens them, modified features could be passed on)

Why is Lamark’s theory wrong

• Traits acquired during life are usually not genetic = therefore not inherited 

• Ex: lifting weights won't make ur kids muscular, tanning doesn’t make ur kids darker

Darwin’s contribution to the theory of evolution

• Natural factors restrict growth

• The environment determines which organisms survive, organisms cannot just “decide to adapt” ex giraffes cannot stretch their necks longer bc they want food, instead nature determines whether a trait is useful or not 

• Advantageous variations were more likely to be passed on 

• Some traits help organisms survive better in a specific environment, so they survive more easily, are healthier, and reproduce more successfully

• All species come from pre-existing species 

What is selective pressure?

• Nature determines adaptations by exerting selective pressures on their inhabitants 

• Selective Pressure = an external agent that makes certain phenotypes more favourable than others

•  example: for giraffes, food located in high trees is a selective pressure

  
  

What is s@xual selection

• =a selective pressure arising through preference by one sex for certain characteristics in individuals of the other

• This is also called “non random mating” 

Definition of the term fitness?

• the ability of an organism to pass its genes on to its offspring and the next generation

What is natural selection?

• the process whereby organisms better adapted to their environment tend to survive and produce more offspring 

• As each generation passes, the strongest/most desirable phenotypes persist (“survival of the fittest”

• This is the main mechanism driving evolution and speciation

Process of natural selection?

1) overproduction of offspring

2) variation within a population

3) struggle for survival

4) differential survival

5) reproduction

What is stabilizing selection?

• Intermediate (middle) variation conveys greater fitness than extremes 

• Meaning that average traits are favored, and extreme traits are selected against

what is directional selection?

• Variations toward one end of the spectrum convey greater fitness 

• Meaning that one extreme trait is favored, and population shifts toward one side 

what is disruptive selection?

• Variations at both extremes convey greater fitness 

• Meaning that both extremes are favoured and middle trait selected against

what is mutation?

• a mutation is a random change in DNA

• Mutations create new alleles (new versions of genes), they are the ultimate source of genetic variation, and without mutations, populations would have no new traits for natural selection act on 

Genetic drift?

• the change in allele frequencies within a population over generations due to random chance

• It’s strongest in small populations

Founder Effect

• a form of extreme genetic drift wherein genetic variation is lost when a new population is established by a small group

• What happens? A few individuals leave a larger population, they carry only a portion of the original genetic variation, the new population develops different allele frequencies

Genetic Bottleneck

• Causes may be things such as: natural disasters, disease outbreaks, overhunting 

• What happens? A large population exists, disaster kills most individuals, survivors represent only a small sample of original genetic diversity, future generations inherit reduced variation

gene flow

•  the transfer of genetic variation from one population to another

• The movement of foreign alleles into established populations influences evolution

• Occurs through migration, movement of pollen/seeds, interbreeding between populations

• Effect: gene flow introduces new alleles, increases genetic diversity and makes populations more simila

speciation?

• the formation of one or more distinct species from a preexisting population

• Caused when one group becomes reproductively isolated from others in the population/gene pool 

• Reproductively isolated = meaning individuals can no longer successfully breed with the original population

Allopatric speciation?

• Speciation caused due to geographical barriers.

• Geographic Barrier: physical barriers such as new rivers, mountain range, desert etc. Because they are physically separated, genetic material cannot be shared. Each isolated population adapts to its unique environment overtime, experiencing different mutations, selective pressures and genetic drift

sympatric speciation?

speciation within the same habitat due to behavioural or temporal changes

abrupt speciation?

• Speciation that happens in one generation as opposed to very slowly 

• Seen in plants 

• This is possible because plants can remain viable even when polypoid 

Polyploidy?

• having more than two complete sets of chromosomes 

• Normal diploid = 2n

• Polypoid = 4n, 6n, 8n 

• Causes speciation because polyploid individuals usually cannot reproduce successfully without diploid individuals. This immediately creates reproductive isolation, therefore a new species can form rapidly

Autopolyploidy?

• polyploidy resulting from intraspecific fertilization by nondisjunction gametes 

• Forms offspring with a higher ploidy number (eg. 2n + 2n = 4n)

Allopolyploidy?

•  polyploidy resulting from interspecific (closely related) fertilization by nondisjunctional gametes

biome?

• a large, naturally occurring community occupying a major habitat 

Habitat?

• the environment in which an organism, population, species or community naturally exists 

Characteristics to describe a habitat?

• Temperature

• Water availability

• Topography (physical features of land)

• Soil type

• Plant and animal species present

• Predators, prey availability 

• Disease presence

• Seasonal changes

Biotic factor?

• living (or once-living) components of an ecosystem 

• Examples: plants, animals, fungi, bacteria 

Abiotic factor?

 non-living environmental components of an ecosystem

Mangrove adaptations?

• salt tolerance/osmoregulator

• anchoring roots

marram grass adaptations?

• water conservation, long leaves in case buried, deep root system, creeper colonization

Limiting Factors?

• an environmental variable that restricts the growth, abundance or distribution of an organism/population?

• Usually due to limited availability or overabundance 

niche?

the ecological space a species exists within and/or the role it plays within the environment at large

2 types of competition?

• Intraspecific competition: competing within the same species 

• Interspecific competition: competition between different species 

Fundamental Niche?

• the theoretical niche that could be occupied by an organism

• The potential of a species based on adaptations and tolerance limits

Realized Niche?

• the actual niche occupied by an organism after factoring in its interactions with other species 

autotrophy?

• the conversion of abiotic sources into energy that is used or stored cellularly 

• ex) plants (from photosynthesis)

heterotrophy?

the consumption of other organisms to serve one’s energy & nutrient needs

Detention

•  the development, arrangement, and condition of teeth in the mouth 

• Teeth are adapted to dietary roles

Herbivores teeth

• Large flat molars, grinding surfaces, reduced canines 

• Helps them grind plant material 

carnivores teeth?

• Sharp canines, cutting teeth, teeth designed to grip prey 

• Helps them capture prey and tear flesh 

Omnivores teeth

• Combination of sharp and flat teeth

• Helps them eat both plants and animals 

Saprotrophy?

•  an organism that feeds on dead or non-living organic matter 

• Also known as extracellular chemoheterotrophy 

• Organisms that do this are called decomposers

Mixotrophy?

•  deriving nourishment both autotrophically and heterotrophically 

• Common amongst protists

• Mixotrophs can be obligate or facultative

      ↪ obligate mixotroph: must perform autotrophy & heterotrophy, needing both to survive

     ↪ facultative mixotroph: can switch between autotrophy or heterotrophy, can survive using one method if necessary 

Archaea

• Have evolved diverse and unique nutritional strategies such as

     ↪ Photoautotrophy (uses sunlight as its energy source and makes its own food from inorganic substances like co2 and water)

     ↪ Chemoautotrophy (makes own food using energy from chemical reactions involving inorganic substances)

     ↪ Heterotrophy (obtains energy n nutrients by consuming other organisms or organic matter) 

• Archaea are difficult to study as their metabolic potential is largely unknown 

Plant Adaptation to avoid becoming food 

• Physical defenses such as thorns or spines to discourage feeding 

• Chemical defenses such as producing toxins to make themselves unpleasant or dangerous to eat