Evolution and Biodiversity (5.1 Evidence for evolution (Pentadactyl limbs…
Evolution and Biodiversity
5.1 Evidence for evolution
Evolution - the changes that occur in living organisms over many generations.
Evolution occurs when heritable characteristics of a species change.
Not possible to prove this theory but there is very strong evidence for it.
Speciation and patterns of variations
Populations of a species sometimes become separated and therefore unable to breed with each other.
This allows them to be able to evolve differently and diverge in their characteristics more.
This process is very gradual and takes place over thousands of years. Eventually they would become so different they would not be able to interbreed again.
The populations have thus evolved into separate species
Pentadactyl limbs as evidence for evolution
4 groups of vertebrates have limbs: amphibians, reptiles, birds and mammals.
The basic structure in these 4 groups have the same basic bone structure. This is known as a pentadactyl limb.
Many different groups have evolved from the common ancestor but because they have developed different types of locomotion the limbs developed in widely different ways to suit the type.
This type of evolution is called adaptive radiation
Structures like pentadactyl limbs that have evolved from a common ancestor are called homologous structures.
Structure contains 5 finger like structures
Selective breeding of domesticated animals
Selective breeding has created a domesticated breed developed from wild species through selecting desirable traits and breeding from them.
Striking differences between the characteristics of domestic and wild breeds gives us evidence that species can evolve rapidly through artificial selection.
The fossil record
Research into fossils has given us strong evidence for evolution.
No fossils can be found of organisms that do exist today, suggesting that organisms change over time.
Rocks can be dated, allowing for the age of fossils to be determined.
Dark varieties of typically light colored insects are called melanistic
The peppered moth is the most famous example. In the 19th century developed to a black color in order to aid its survival in areas of higher pollution.
5.2 Natural Selection
Sources of variation
The original source of variation. New alleles are produced by gene mutation, which enlarges the gene pool of a population.
Produces new combinations of alleles by breaking up existing combinations in a diploid cell. Every cell produced by meiosis is an individual is likely to carry a different combination of alleles because of crossing over and independent orientation of bivalents.
involves the fusion of male and female gametes. The gametes usually come from different parents, so the offspring has a combination of alleles from two individuals.
Observations and deductions
Species tend to produce more offspring than the environment can support.
There is a struggle for existence in which some individuals survive and some die.
In natural populations there is a variation between the individuals
Some individuals are better adapted than others.
Individuals that are better adapted tend to survive and produce more offspring.
Individuals that reproduce and pass on characteristics to their offspring.
The frequency of characteristics that make individuals better adapted increases and the frequencies of other characteristics decrease, so species change and become better adapted.
Heritability and evolution
acquired characteristics are not inherited by offspring.
Beaks of finches on the Daphne major
Variation of beak sizes which is a heritable characteristic
Varying climates can determine the availability of small or large seeds.
From 1974 - 1977 la Nina conditions were experienced ending with a severe drought which resulted in the population dropping from 1,300 to 300.
Mean beak size of those that survived were significantly bigger than those that died. The opposite happened in 1983 when there was an el nino event which resulted in the mean size dropping as small soft seeds were abundant.
Antibiotic resistance in bacteria
Evolution by natural selection can explain the development of antibiotic resistance in bacteria.
Genes that give resistance to an antibiotic occur in microogranisms that naturally make that antibiotic.
Doctors or vets that use the antibiotic to control a bacteria will kill bacteria that are susceptible to the antibiotic, but not those that are resistant. This is an example of natural selection.
Antibiotic resistant bacteria can reproduce and pass on the resistance gene to their offspring.
The more an antibiotic is used the more bacteria resistant to it there will be and the fewer that are non-resistant. As a result of excessive use most bacteria may eventually be resistant.
5.3 Classification of Biodiversity
First name is the genus name. A genus is a group of closely related species.
The genus name is given an upper case first letter
The second name is the species name given with a lower case first letter.
Italics are used when a binomial appears in printed or typed document.
Done using dichotomous key
Series of numbered stages.
Each stage consists of a pair of alternative characteristics.
Some alternatives give the next numbered stages of the key to go to.
eventually the identification of a species will be reached.
Biologists that specialize in classification are taxonomists.
allow the prediction of characteristics shared by species within of a group and can also help in the identification of species.
Animals could be classed into two groups
Domain -> Kingdom -> Phylum -> Class -> Order -> Family -> Genus
Hierarchy of taxa
Genus > Balaenoptera
A group of organisms such as a species or a genus is called a taxon