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Adaptation and Evolution. Evolution is the change in the inherited traits of a population of organisms through successive generations Two factors at work: Processes that constantly introduce variation in traits Processes that make particular variants become more common or rare. Evolution.

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Evolution is the change in the inherited traits of a population of organisms through successive generations

  • Two factors at work:
    • Processes that constantly introduce variation in traits
    • Processes that make particular variants become more common or rare

Variation is introduced to a population’s gene pool by:

    • Mutation: a heritable change in the nucleotide sequence of the genetic nucleic acid
    • Gene flow: introduction or loss of new alleles into the population through immigration or emigration
    • Genetic drift: stochastic shifts in allele frequencies in small populations
    • Natural selection: change in allele frequencies over generations due to differential survival and reproductive success of genotypes
types of mutations1

Chromosomal mutations occur when chromosomes fail to properly separate during meiosis


Structural Modification Irregular Number

why do genes mutate

Scientists disagree about how and why genes mutate

  • For a long time they believed that genetic mutations were unrelated to whatever consequences such mutations would have on the species.
  • Researchers have found evidence that cells might be able to "choose" which mutations will occur to give them an advantage in stressful situations.
    • For example, when starving, certain bacterial cells might generate multiple mutations. If the mutated cell survives, the mutation is passed on; cells that die take their unsuccessful mutations with them.
    • Flexibility in antibody production
Why do genes mutate?
gene flow
Gene Flow

Wilson & Bossert, 1971

genetic drift

In each generation, some individuals may, just by chance, leave behind a few more descendents than other individuals

The genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better” individuals

It happens to ALL populations—there’s no avoiding the vagaries of chance

Genetic Drift

Fitness is a measure of the ability of an individual to produce viable offspring and contribute to future generations

    • Individuals vary in their relative fitness due partly to genetic differences among individuals and partly to environmental influences
  • Individuals with greatest fitness will contribute disproportionately to subsequent generations

As the environment changes so do the fitness values of the genotypes

  • Some properties of fitness:
    • Fitness is a property of a genotype, not of an individual or a population
    • Individuals with the same genotype share the same fitness within the same environment
    • Fitness is measured over one generation or more
survival of fit enough

Natural selection may not produce a “perfectly-engineered” trait

  • Reasons why natural selection might not produce perfection
    • Lack of necessary genetic variation
    • Constraints due to history
    • Trade-offs
Survival of “Fit Enough”

Adaptation is the evolutionary process whereby a population becomes better suited to its habitat

    • Important for an organism's survival
  • Adaptations may be:
    • Physiological
    • Morphological
    • Behavioral
  • Adaptation is the result of natural selection

An adaptation is a feature that is common in a population because it provides some improved function

Adaptations are well fitted to their function

A vestigial structure is a feature that was an adaptation for the organism’s ancestor, but that evolved to be non-functional because the organism’s environment changed

ecology and evolution

What are selection pressures in an organism’s environment?

    • Biotic factors
      • Predation
      • Competition
      • Mutualism
    • Abiotic factors
      • Resource availability
      • Physical conditions
      • Chemical conditions
Ecology and Evolution
1859 rabbits brought to australia

No predators

Exponential growth

Environmental and crop damage

1859 Rabbits brought to Australia
myxoma virus control

Introduced in 1950

Initially highly effective

Reduced rabbits by 99%

Now mortality rate is less than 50%

Myxoma virus control
natural selection

Over many generations, mutations produce successive, small, random changes in traits, which are then filtered by natural selection and the beneficial changes retained

Traits become suited to an organism's environment: these adjustments are called adaptations

Ok: Survival of the fittest Better: those that can --- survive

Natural Selection