Evolution

Day 1

What is Evolution?

• Evolution is defined with the idea that living species are descendants of ancestral species that were different from present

• Over a long period of time, the effect of these small changes can result in multiple idfferent species evolving from the same ancestral species. It is a branching tree.

• Adaptive Radiation is a process in which organsisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, alters biotic interactions or opens new niches.

What is Natural Selection

• Natural Selection is the process by which individuals with advantageous traits are more likely to survive and reproduce, thereby passing those traits on to the next generation, leading to gradual changes in the population over time.

Darwin’s argument can be summarized by two observations from which two inferences were made.

Observation 1: Members of a population often vary in their inhereited traits (phenotypes)

Oberservation 2: All species are capable of producing more offspring than the environment can support, leading to a struggle for existence among individuals.

Inference 1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals

Inference 2: This unequal ability of individuals to survive and reproduce will lead to the accumilation of facorable traits in the populataion over generations.

Key Terms:

• Adapations are inheretied traits that increase an organism’s probability to survive and reproduce.

• Fitness is when the organism has the right adaptations for its environment.

Individuals don’t adapt and evolve - populations do

• Jean-Baptiste Lamarck proposed that organisms have an innate desire to improve themselves, and they can pass on traits acquired during their lifetime to their offspring.

• Individual organisms do not adapt to their environment!!

• An organism cannot acquire new adaptations after it is born.

Summary

• Individuals with certain heritable traits survive and reproduce at a higher rate than other individuals

• Natural selection increasees the match between organisms and their environment over time

• If an environment changes over time, natural selection may result in the population adapting to these new conditions and may give rise to new species

• If there is a rapid change in an environment, the adaptiation has to change before.

Evidence of Evolution

Direct Observation-The Evolution of Antibiotic resistant to mechillin

• When exposed to methicillin, MRSA strains are more likely to survive and reproduce than nonreistant S. aureus strains.

Selective Breeding/Artificial Selection

• Humans have been mimicking the process of evolution for thousands of years through selective breeding.

• By selectivley breeding those individuals with desire characteristics, humans have chnages mnay agricultural crops and domesitcated animals.

Fossil Record

• The fossil record provides evidence of extinction of species, the origin of new groups, and changes within groups over time

  • They can document important transitions. The deeper you go, the older it gets.

Anatomical Homologies

• Homology is similarity resulting from common ancestry

• Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor

• Vestigial Structures are remnants of features that served important functions in the organism’s ancestors

Molecular Homologies

• Examples of homologies at the molecular level are genes shared among organisms inherited from a comm ancestor

• The fact that all organsims on Earth use the same genetic code is on eof the strongest pieces of evidence that all life shares a common ancestor

Convergent Evolution

• Convergent Evolution is the eveolution of similar, or analogous, features in distantly related groups

• Analogous traits arise when groups independantlly adapt to similar environmnets in similar ways.

• Convergent evolution DOES NOT provide info about ancestry, it demonstrates how natural selection shapes species

Day 2-Microeveolution

Populations and Gene Pools

A population is a localized group

What is microevolution?

• MIcroevolution is the change in allele frequencies of a population’s gene pool over generations.

• Speciation is the formation of a new species

• Macroevolution is a broader scale evolutionary changes that happen over a paleontological time scale.

Is a population evolving? If it is what’s causing it?

• A population whose allele frequencins remain constant over generations is said to be at Hardy-Weinberg Equilibrium

Equilibrium or Evolution? It depends on 5 conditions

Hardy-Weinberg Equation: A mathematical model that describes the genetic variation in a population at equilibrium, allowing us to understand how immigration and emigration can affect allele frequencies.

p+q=1

p represents the frequence of the dominant allele in a population

q represents the frequencey of the recessive allele in a population

p²+2pq+q²=1

p² represents the frequency of the homozygous domninant genotype(BB)

2pq represents the frequency of the heterozygous genotyoe(Bb)

q² represents the frequency of the homozygous recessive genotype(bb)

Day 3

Natural Selection: Directional, Disruptive, or Stabilitizing

In Directional Selection, one of the extreme phenotypes is the most advantagerous(selected for), while the other extreme phenotype is the most disadvantagrous(selected against).

In Disruptive Selection, the two extreme phenotypes are very advantagrous (selected for), while the intermediate phenotype is the most disadvantageous (selected against).

In Stabilizing Selection, the intermediate phenotype is the most advantageous(selected for), while the extreme phenotypes are the most disadvantagrous(selected for).

Genetic Drift

• Genetic Drift DOES NOT involve mutations or selection of any kind.

• Genetic drift changes allele frequencies due to random chance.(Survival of the Luckiest")

• Bottleneck Effect- A large population can become a small population through a catastropgic event that wipes out most of the populaation.

• Founder Effect- A small group from a large population can relocate to another location, and this becomes a new population.

  
  

Day 4

Cladograms/Phylogentic Trees

A cladogram is a branchin diagram that represents a hypothesis about the evolitionary historyu(phylogeny) of a group of ogransisms(clade)

Root-Base of the tree that represents the common ancestor for all organisms

Outgroup- he group that has the least in common with everything else.

Derived character-A feature that distinguishes one group from another

Node- Point of divergence between lineages and represents most common ancestor.

Higher node= more recent common ancestor

Day 5

Speciation

Genetic variation-There are varaiations in the traits of the individuals of the species.

Geographic variation- There are also different variations in the population found in the different areas

Selection pressures- Each population would have slightly different slection pressures

• There has to be a population that is reproductively isolated.

  • There will be now gene flow in the population that is isolated.

• After a long time, the population may become genetically different enough for it to be now classified as a new, but closely related species.

Punctuated Equilibrium vs Gradualism

Punctuated Equilibrium- Proposed by Niles Eldredge and Stephen Jay Gould and states that evolution occurs in rapid bursts of change followed by long periods of sasis(little or no change). Rapid changes often occur due to sudden environmental shifts or isolalation

Gradualism- The theory that new species evolve from existing species through gradual, often impreceptible changes rather than through abrupt, major chnages,

What is a species?

• The biological species concpet defines a species based on reproductive compatibility

  • A species is a group of populations whose members have the potential to interbreed in nature and produce viable fertile offpring

Allopatric Speciation vs Sympatric Speciation

• Allopatic speciation is when gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations

• Sympatic speciation is when speciation takes place in geographically overlapping population.

Types of Reproductive Barriers

• They prevent gene flow

• Prezygotic barriers block mating attempts or prevent fertilization from Equilibrium

  • Habitat isolation where two species encounter rarely, because they occupy differnt habitats, even though not isolated by physical barriers

  • Temporal Isolation where species that breed at different times of the day, different seasons, or different years cannot mix their gametes

  • Behavioral isolation where courtship rituals and other behaviors unique to a species are effective barriers to mating

  • Mehcanical Isolation where morphological differences can prevent successful completion on mating

  • Gametic Isolation is when the make gametes of one species may not be able to fertilize the famale gamete of another species

• Postzygotic Barriers

  • Reduced hybrid viability where genes of the different parent species may interact and impar the hybrid’s development or survival in its environment.

  • Reduced hybrid fertility where even if hybrids are viable, they may be infertile

  • Hyrbid brealdown where some first generation hybrids are fertile, but when they mate with each other or with either preant species, offspring of the next generation are feeble or sterile

Polyplpoidy and sympatric speciation

• Polploidy is the presence of extra sets of chromosomes due to accidents during cell division

  • is much more common in plants than in animals because plants and self fertlie