evolution

Variation

Some organisms are exact clones and have the same genotype, but there will be slight changes in phenotype as a result of the different environment they live it or different interactions with other organisms they have had.

Genetic variation is the variation in genotypes that exist within a species.

Phenotypic variation is the variation that is visible or detectable within a species.

Interspecific variation is variation between species

Intraspecific is variation within species

This variation is due to genetic differences between individuals but also the effect of the environment, as well as interactions between genes and the environment

Interspecific

The variation between species

Intraspecific

The variation within species

Discontinuous variation

Variation in a feature that has discrete categories without intermediates, e.g. blood type.

Most examples of discontinuous variation are controlled solely by genes and the environment usually have no effect on the expression of these genes in the phenotype.

Discontinuous variation- human blood groups

There are two genes involved in controlling human blood groups.

Gene on chromosome 9 controls the ABO system which has phenotypes- A,B,AB and O.

The gene codes for an enzyme that adds a sugar molecule on a glycoprotein situated in the cell surface membrane of erythrocytes.

The other blood group system is the Rhesus system controlled by a gene on chromosome 1- either r or R.

This gene codes for an erythrocyte transmembrane protein.

Continuous variation

Variation in a feature that shows a range of phenotypes between two extremes with many intermediates

Examples: height, body mass

Continuous variation is controlled by both genes and the environment- influenced by polygenes

Causes of variation

Features that show discontinuous variation are controlled mainly or entirely by genes, environment has little to no effect.

Features that show continuous variation are influenced by both genes and the environment.

E.g. body mass of mice may be due to stored fat from eating or an allele that gives rise to obesity (result of mutation and is recessive)

Aspects of variation that are only caused by the environment, a scar from damage.

Many genes have two or more alleles- allozymes are enzymes variants that are coded by different alleles at the same gene.

Adaptation

The way a structure, function or aspect of behaviour helps an organism to survive in its own environment or perform an activity such as feeding or evading predators.

Involves all aspects of an organism- morphology, anatomy, physiology (function of its body system), biochemistry (chemistry of cells), reproduction and life cycle.

Some of the best places to find a structural, behavioural and physiological adaptation are in extreme environments.

Structural features: physical characteristics of an organisms body that help it to survive.

Behavioural features: ways in which an organism acts to help it survive and reproduce.

Physiological features: internal processes and functions that help an organism survive.

Convergent evolution

Unrelated species evolve similar features due to similar environmental pressures

Lead to analogous structures- different origin and same function

Divergent evolution

Organisms that share a common ancestor become increasingly different overtime as they adapt to different environments or selection pressures.

Different mutations arise and different alleles are selected- causing population to diverge genetics;lay and phenotypicslly.

Produces homologous structures- same evolutionary origin, different functions

Darwin’s observations

In developing his theory of natural selection, Darwin made four observations:

All organisms give far more offspring than are ever going to survive.

Populations of organisms fluctuate but do not tend to increase or decrease significantly overtime

There is variation among many individuals in many of their characteristics- inter specific variation, arises in each generation where organisms reproduce sexually to produce offspring.

Offspring resemble their parents- features transmitted from one generation to another.

Darwin explore the consequences of these observations and made the following inferences:

There is competition between organisms in the same population for limited resources.

Organisms successful in competing for resources have features which means they are adapted to their environment- higher chance of surviving and live longer to reproduce.

Unequal ability of individuals to survive and reproduce leads to a gradual change in population, with certain adaptations increasing in frequency over generations.

Competition

Environmental factors may control sizes of population of heterotrophic organisms such as food, water, disease and predation.

Populations of autotrophs are controlled by disease and grazing but also access to carbon dioxide, light, water and mineral ions.

Poorly adapted organisms have a lower chance of surviving and higher risk of dying before they have the chance to reproduce.

Natural selection

Organisms better adapted to gain resources, avoid catching lethal diseases and escape being eaten alive are likely to survive long enough to find a mate and pass of their alleles to future generations.

These organisms are better adapted than others.

When environment is stable, natural selection acts to maintain the features of a species but if environment changed then the selection pressures in an environment also change.

This means organisms with features that were previously disadvantageous are now the ones that compete well, survive and breed.

Evidence for evolution

Comparative morphology- the similarities in outward appearance of organisms; for example, all birds have beaks.

Comparative anatomy- for example, the same basic patterns of bones in the limbs of all tetrapods.

Fossilised remains of organisms and other fossilised traces (such as footprints, burrows and organic chemicals made by organisms) that are discovered in rocks.

Comparative biochemistry-many bio chemicals are found in all organisms which suggests that they have a common origin, similarities and differences between proteins and DNA provide evidence for evolutionary relationship between organisms.

Classification reflects phylogeny groups of organisms.

Evidence from fossils

A fossil is a mineralised or otherwise preserved remains of an animal, plant or microorganism.

May also consist of other traces of organisms such as, footprints, burrows or faeces.

Found in sedimentary rocks and chemical traces of fossils have been found in metamorphic rocks.

Oldest fossils are those of prokaryotes.

Rocks can be dated by a chemical analysis.

Also by looking at alignment of layers or strata of rocks we can put fossils in a sequence that reveals changes that happened in line of descent.

Studying fossils provides evidence for the gradual change from simple life forms to more complex life forms.

Comparing morphology and anatomy of species in order show evolutionary relationships.

Evidence from biochemistry

The atoms in amino acids can be arranged to give two molecules that are mirror images of each other.

20 amino acids used to make proteins.

Molecules of inheritance in all cellular organisms is DNA.

The genetic code that specifies an organisms amino acid is basically the same in all organisms.

ATP is the universal currency for energy in the cells of all organisms.

Analysis of amino acid sequences of proteins reveal that proteins from closely related organisms are very similar.

Active site of enzymes like catalase tend to be identical whatever the organism it comes from as no other arrangement of amino acids gives the right 3D shape to fit the specific substrate.

Looking at enzymes form different organisms reveals that differences become greater the less related they are.

Some enzymes perform basic functions found throughout all life forms such as DNA polymerase- which has relatively small differences in its amino acid sequence between phyla and even between kingdoms.

Significant changes in enzyme reflect significant events in the evolutionary history of organisms.

Primary structure of proteins is determined by sequence of DNA bases in DNA.

Data collected from these sequences shows the relationship between different species.

Nucleotide sequences in closely related species are found to be very similar.

Similarities and differences can be used to group species and also gives an idea of when speciation occurs.

Drug reistance

Antibiotics are used to treat bacterial diseases.

Bacteria has become less effective due to antibiotic resistance

Resistant bacteria is at an advantage as they are adapted to new conditions.

Resistant bacteria survive and reproduce to pass on genes to future generations

Two ways bacterium gains antibiotic resistance:

Gene on chromosome may mutate- form polypeptide not affected by antibiotic

Bacterium gains a plasmid with a gene for resistance from another bacteria, even from an individual of different species.

Genes may code for an enzyme to break down the antibiotic.

May pump out any antibiotic molecules that enter the cell.

Changing protein structure means antibiotics cannot inhibit action of enzymes and proteins involved in replication, transcription and translation of bacteria.

Bacteria have one copy of each gene- haploid.

Bacteria without mutant gene will be killed.

Bacteria reproduces asexually through binary fission.

Dose must be taken correctly otherwise less susceptible bacteria survive and next time antibiotic may not be effective.

How to reduce antibiotic resistance

Only prescribe antibiotics when absolutely necessary.

Ensure people finish their course of antibiotics.

Rotate antibiotics so one type isn’t continuously used in the treatment of specific diseases.

Keep some antibiotics to use as a last resort.

Invest in research to find new antibiotics.

Pesticide resistance in insects

Pesticides are chemicals that kill any sort of pest, pathogen or weed.

Used to control insects.

Pests cause massive damage to crop plants in monocultures and reduce yields significantly.

Any insect resistant to pesticide will survive and reproduce as there will be less competition.

Insecticides act as selective agents (any factor in the environment of an organism that influences the survival of that organism and so brings about natural selection).

Farmers should use multiple pesticides as it delays time for resistance to emerge and spread.

VOSSUG

Variation

Overproduction- more offspring than can survive

Selection- more advantageous alleles better able to survive in their environment- have a selective advantage.

Survival of the fittest- organism with advantageous allele more likely to survive and reproduce- passing alleles to offspring

Useful characteristics- inherited by offspring- increased allele frequency in the population

Gradual change- over many generations this occurs

Speciation

Process of a new species evolving due to evolution by natural selection

It can happen through physical separation of population

Different environment results in different selection pressures- provides different alleles in the two places

Two populations can no longer reproduce to produce fertile offspring