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/evo101/IIIDGeneticdrift.shtml