examples of evolution grade 10 biology spring 2011
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Identify four elements in the process of natural selection
Describe how natural selection has affected the bacteria that cause tuberculosis
Relate natural selection to the beak size of finches
Summarize the process of species formation
In small groups brainstorm to identify characteristics of birds that provide information about their diets
Natural selection is the mechanism that drives evolution
Environment dictates the direction and amount of change
If the environment changes in the future, the set of characteristics that most help an individual reproduce successfully may change
All populations have genetic variationIn any population there is an array of
individuals that differ slightly from each other in genetic makeup
The environment presents challenges to successful reproduction An organisms that does not survive to
reproduce or whose offspring die before the offspring can reproduce does not pass its genes on to future generations
Individuals tend to produce more offspring than the environment can support Individuals of a population often compete with
one another to survive
Individuals that are better able to cope with the challenges presented by their environment tend to leave more offspring than those individuals less suited to the environment do
Mycobacterium tuberculosis: In the 1950’s effective antibiotics, isoniazid and
rifampin, became available and saved many lives
In the late 1980’s new strains of M. tuberculosis that are largely or completely resistant to the antibiotics appeared
Rates of TB began to skyrocket
How did M. tuberculosis evolve?A man was treated with rifampin for an active
TB infectionAfter 10 months the antibiotics cleared up the
infectionTwo months later, man was readmitted to the
hospital with a severe TB infection, and despite rifampin treatment, he dies 10 days later
Strain of M. tuberculosis isolated from his body was completely resistant to rifampin
How did M. tuberculosis evolve?Comparison of DNA of rifampin-sensitive
M. tuberculosis to rifampin-resistance M. tuberculosis
Only one difference, a single base change from cytosine to thymine in a gene called rpoB
Rifampin acts by binding to M.tuberculosis RNA polymerase, preventing transcription and so killing the bacterial cell
Mutation in polymerase’s rpoB gene prevents rifampin from binding to the polymerase
Mutation does not destroy polymerase’s ability to transcribe mRNA
Because its polymerase function was no longer normal, the mutant bacterium could not divide as rapidly as normal bacteria can, but it still could divide
The antibiotic caused the normal bacterial cells to eventually die
The mutant bacteria continued to grow and reproduce in the antibiotic-containing environment
Because the total number of M. tuberculosis bacteria was reduced drastically by the first antibiotic treatment, the patients infection had seemed to clear
Mutant antibiotic resistant bacteria had survived and continued to grow
The mutant bacteria could produce more effectively in the presence of the antibiotic than the normal bacteria
Mutant bacteria became more common in the bacterial population and eventually became the predominant type
When the patient became ill again the M. tuberculosis were the rifampin-resistant cells
In this way, natural selection led to the evolution of rifampin resistance in M. tuberculosis
Darwin collected 9 distinct species of Finches, all very similar to one another except for their bills
Large bill- fed on seeds they crush in their mouths
Narrow bill- eat insects One was a fruit eaterOne picks insects out of cactus Another creeps up on sea birds and drinks
their blood
Darwin suggested the Finches all evolved from an original ancestral species
Changes occurred as different populations accumulated adaptations to different food sources
Study over 25 years showed:During wet years birds with different beak
sizes ate the plentiful small, soft seeds During dry years, plants produce few seeds,
large or smallDuring dry years, few small, soft seeds were
availableDifference between survival and starvation is
the ability to get the larger, tougher seeds that most birds usually pass by
Study over 25 years showed:Measured beaks, found that after several dry
years, the birds that had longer, more massive beaks had better feeding success and produced more offspring
When wet season returned birds tended to have smaller beaks again
The numbers of birds with different beak shapes are changed by natural selection in response to the available food supply
Divergence: the accumulation of differences between groups Divergence leads to the formation of a new
speciesSpeciation: process by which new species
forms
Separate populations of a single species often live in several different kinds of environments
In each environment, natural selection acts on the population
Over time, populations of the same species that different genetically because of adaptations to different living conditions become subspecies First step toward speciation If get so different they cannot interbreed are
considered separate species
Once subspecies become different enough, a barrier to reproduction, prevents different groups from breeding with each otheri.e. time of peak mating activity could be
different
Types of barriers that may isolate closely related species:Groups may be geographically isolatedMay reproduce at different timesPhysical differences may prevent matingMay not be attracted to one another for mating Hybrid offspring may not be fertile or suited to
the environment of either parent
1. List four examples of natural selection 2. Describe how speciation takes place3. The beaks of finches on the Galapagos
Islands enlarged over generations in response to:
a) Isolation b) Pollutionc) Rain d) Limited food supply
1. Four examples of natural selection: genetic variation, environmental challenges to reproduction, overproduction of offspring and a struggle for survival, an increase in the number of individuals with characteristics suited to the environment
2. Speciation takes place as populations of species spread through an environment, they are exposed to varying conditions; over time the separate populations become distinct and split into subspecies, and eventually separate species
3. The beaks of finches on the Galapagos Islands enlarged over generations in response to:
a) Isolation b) Pollutionc) Rain d) Limited food supply
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