Bio Unit 8: Evolution

Have a working knowledge of Natural Selection, Hardy Weinberg Theory, Evolution of populations, Genetic Drift, Bottleneck Effect, Founder Effect, Gene Flow, Homologous and Vestigial Structures

• Evolution:

  • occurs to a population not just an individual

  • 4 steps:

    • Variation

    • Competition

    • Adaptations

    • Selection

• Natural Selection:

  • mechanism of evolution (individuals with certain traits are more likely to survive and reproduce… NOT RANDOM)

  • survival of the finest —> occurs naturally in the environment

  • 5 basic steps:

    • Variation

    • Inheritance

    • Selection

    • Time

    • Adaptation

  • unequal reproduction

    • some individuals don’t evolve

    • can amplify/diminish only heritable traits

    • evolution isn’t goal-directed

• Hardy Winberg Theory:

  • 𝑝 + 𝑞 = 1 (*alleles, dominant vs. recessive)

  • 𝑝² + 2𝑝𝑞 + 𝑞² = 1 (*genotypes, homo dominant vs. hetero vs. homo recessive)

  • Assumptions:

    • no selection

    • no mutation

    • no migration

    • large population

    • random mating

• Evolution of populations:

  • population: a group of organisms all the same species and can breed w/ each other

• Genetic drift: change in frequency of an existing gene variant in the population due to random chance (more pronounced in smaller populations bc fewer contributing to next generation’s gene pool)

  • Founder effect:

    • small group of individuals breaks off (migrate) from a larger population to form a new population

    • the new population's gene pool may not represent the original population's genetic diversity

  • Bottle-neck effect:

    • significant reduction in population size (due to events like natural disasters) can lead to a genetic bottleneck, where the surviving population has reduced genetic diversity

  • Genetic drift vs. natural selection:

    Aspect	Genetic Drift	Natural Selection
    Process Type	Random	Non-random
    Population Size	Effects more significant in small populations	Can occur in any population size
    Role of Environment	No direct influence	Direct influence (selective pressures)
    Effect on Allele Frequencies	Random fluctuations	Increases frequency of advantageous alleles
    Genetic Variation	Can decrease genetic variation	Can maintain or increase genetic variation
    Outcome	Potential loss of alleles or fixation by chance	Adaptation to the environment
    Examples	Bottleneck effect, founder effect	Industrial melanism in peppered moths, antibiotic resistance in bacteria

• Gene Flow:

  • any movement of individuals or genetic info they carry from one population to another (due to movement of individuals)

• Homologous and Vestigial structures:

  • Homologous/divergent:

    • similarity in characters resulting from shared ancestry

      • different species but similar bc common ancestry

  • Vestigial:

    • “leftover” structures; served an important function in ancestors

  • analogous/convergent:

    • organs w/ similar functions (not ancestry related)

  Define the terms Adaptation and Speciation.

• Adaptation:

  • organisms experience change in their traits to be better suited for the environment

• Speciation

  • the evolutionary process by which populations evolve to become distinct species (over time and possibly bc of isolation)

Understand the role of gene mutations and how they can only be passed on to the offspring if they occur in an organism’s sex cells.

• mutations are the source of genetic variation

• mutations in sex cells can be passed down to offspring

Explain why increased genetic diversity tends to improve the survival of a species.

• increased variety of traits —> bigger likelihood of survival

• decreased inbreeding —> less genetic disorders

• interact in more stable and complex ways within ecosystems.

Explain the following examples of evolution in modern times in terms of the theory of natural selection: the peppered moth, insect resistance to insecticides, and bacterial resistance to antibiotics.

• peppered moth:

  • in very polluted places, darker moths are favored bc blend in better

• inesct resistance to insecticides:

  • as we use more insecticides, the insects that are able to withstand and survive the chemicals reproduce —> then more of the insects become immune to the pesticides (immunity passed down through reproduction)

• bacterial resistance to antibiotics:

  • Overuse and misuse of antibiotics have accelerated the evolution of antibiotic-resistant bacteria

  • Resistant bacteria survive antibiotic treatment and reproduce so frequency of resistant bacteria increases, leading to the spread of antibiotic-resistant strains.

Define and understand the terms: heterozygote advantage, balancing selection, and frequency-dependent selection.

• heterozygote advantage:

  • heterozygous genotype has relatively greater fitness than homozygous recessive/domninant

  • greater reproductvie success of heterozygous individuals

    • preserves variation in gene pool

• Balancing selection:

  • a type of natural selection that maintains genetic variation within a population by favoring multiple alleles at a particular locus over time.

    • prevents any allele from being fixed

• Frequency-dependent selection:

  • fitness of a genotype depends on proportion of individuals w/ certain genotypes in the population

Define and understand the following selection patterns: directional, disruptive, & stabilizing, and their impact on evolutionary fitness.

Understand key points associated with evidence of evolution.

• fossil record

• comparative anatomy

• molecular biology

• biogeography

• direct observation

• comparative embryology

Reading cladograms

• The main line of a cladogram represents the passage of time.

  

Additional Videos:

• Evidence for evolution:

  • Direct observation

    • mutation happens by chance, passed on through natural selection

  • Homology

    • structural similarities (results of common ancestry)

  • Vestigial Structures

    • features that are not useful to an organism & must be remnants of ancestral features (ex. wisdom teeth)

  • molecular homology:

    • we can gauge how closely related species are by comparing their genomes

  • fossil record:

    • get an idea of what kind of organisms existed + when

  • Biogeography:

    • following change in geography helps us make fossil predictions

• Factors that guide evolution:

  • genetic variation makes evolution possible

  • genetic drift: shows chance events gradually alter the gene pool

    • can alter allele frequencies and lead to loss of genetic variation

  • founder effect: deviations amount founders (smaller group) are statistically significant

  • bottleneck effect: original population—> catastrophic event —> survivors

    • deviations among survivors are statistically significant

  • gene flow: occurs to migration of fertile organisms

• Sexual selection and sexual dimorphism:

  • adaptations that help organisms attract/select mate

  • intersexual selection:

    • one sex chooses which members of the opposite sex to mate w/

  • intrasexual selection:

    • members of the same sex compete for mates