ADAPTATION AND EVOLUTION

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 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 MUTATIONS: Point mutations are caused by random

errors in the copying process (during transcription)

Point mutation

TYPES OF MUTATIONS: 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

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

BOTTLENECK

FITNESS 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

FITNESS 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

ADAPTATION 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

ADAPTATION 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

Natural selection leads to adaptive radiation and speciation

SELECTION CAN BE…

“natural” or anthropogenic…

BEAK ADAPTATION

1859 RABBITS BROUGHT TO AUSTRALIA No predators Exponential growth Environmental and crop damage

MYXOMA VIRUS CONTROL Introduced in 1950 Initially highly effective Reduced rabbits by 99% Now mortality rate is less than 50%

DESCRIBE CHANGE IN RABBIT POPULATION

DESCRIBE CHANGE IN MYOMA VIRUS

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

SOURCES http://evolution.berkeley.edu/evosite/ev

o101/IIIDGeneticdrift.shtml