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Evolutionary Theory and Biodiversity Cheat Sheet

A Education › Biology cheat sheet in English by ArcelM4

Grade 12 Study on Evolution and Biodiversity

Biology Evolution Grade12
11,823 views 903 downloads 7 Sep 2025 History
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Important People

James Hutton (1726-­1792) and Charles Lyell (1797-­1875)
Studies unifor­mit­ari­anism and concluded that Earth is extremely old, changing over time due to natural processes.
Erasmus Darwin (1731-­1802)
Suggested that compet­ition between indivi­duals could lead to changes between species.
Jean Baptiste Lamarck (1744-­1829)
Proposed a mechanism by which organisms change over time and that living things evolve through the inheri­tance of acquired charac­ter­istics.
Thomas Malthus (1766-­1834)
Observed that human popula­tions cannot keep growing indefi­nitely. If the birth rate was higher than the death rate then all resources would be used up.
Charles Darwin (1809-­1882)
Formulated a theory of evolution by natural selection based on observ­ations made on his voyage on the HMS Beagle and of selective breeding.
Alfred Russel Wallace (1823-­1913)
Proposed a theory of evolution similar to Darwin­'s and wrote a paper to Darwin to be reviewed, which made him release his theory.

Types of Natural Selection

Types of Natural Selection
Red = Before Selection
Blue = After Selection

Microe­vol­ution

Microe­vol­ution
Describes changes that occur within a population of a single species. It includes the process of natural selection, changes in allele freque­ncies, and changes in popula­tions that result over time.
Macroe­vol­ution
Describes large-­scale and long-term evolut­ionary patters among many species. The evolution of species from a common ancestor
Processes of Microe­vol­ution
Mutation, Natural Selection, Genetic Drift, Gene Flow
Mutation
Changes in the DNA sequence
Natural Selection
Survival of the fittest
Genetic Drift
Shift in the allelic freque­ncies due to chance. Specif­ically affects small popula­tions.
Gene Flow
Movement of indivi­duals both in and out of a gene pool.
Popula­tions evolve, not indivi­duals.

The percentage of any specific allele in a gene pool is an allelic frequency and when the frequency stays the same for a long period of time it's called genetic equili­brium.

Two Examples of Genetic Drift

Bottleneck Effect
Results from near extinction of a species.
Founder Effect
Results from a small number of indivi­duals colonizing a new area.

Hardy-­Wei­nberg Principle

The Hardy-­Wei­nberg Principle
A mathem­atical model that deals with the freque­ncies of alleles in a gene pool. If the allelic frequency does not change in a population over successive genera­tions, then evolution does not occur and the popula­tions is at an equili­brium.
Condition 1.
No mutations occur so that the gene pool does not change.
Condition 2.
Emigration and immigr­ation do not occur as the would alter the gene pool.
Condition 3.
The population must be large so that changes do not happen by chance alone.
Condition 4.
All mating must be totally random so that one form of allele is not favoured over the other.
Condition 5.
All forms of the allele must be expressed equally well so that there is no natural selection.
It is virtual impossible to meet these condit­ions, allelic freque­ncies do change in popula­tions and evolution does occur. This principle also useful in explaining why genotypes within a population tend to remain the same, as well as for determ­ining the frequency of a recessive allele.

Hardy-­Wei­nberg Principle Example 2

While studying a sample of pea plants, you find that 36 of 400 plants were short (reces­sive). The rest were tall.

q =
p =
q2 = 36/400
p2 =
2pq =
↓
q =
p =
q2 = 0.09
p2 =
2pq =
↓
q = √0.09 = 0.3
p =
q2 = 0.09
p2 =
2pq =
↓
q = √0.09 = 0.3
p = 1-0.3 = 0.7
q2 = 0.09
p2 = 0.72 = 0.49
2pq = 2(0.7*0.3) = 0.42
↓
0.42+0.49­+0.09=1

Convergent and Divergent Evolution

Divergent Evolution
The process in which an ancestral species gives rise to a number of new species that are adapted to different enviro­nmental condit­ions.
Homologous Structures
Refers to the structural features with common evolut­ionary origins. The structure is the same, but the function is different. It is evidence that organisms evolved from a common ancestor.
Convergent Evolution
The process in which different organisms that live in similar distant habitats become more alike in appearance and behaviour.
Analogous Structures
Refers to the evolution of body parts of organisms that do not have a common evolut­ionary origin but are similar in function. Dolphins and sharks live in the water and both use tails for propul­sion, but their tails are from different origins.

Divergent vs Convergent Evolution

Divergent vs Convergent Evolution

2 Models of the pace of evolut­ionary change

Gradualism
Describes the pattern of flow and gradual change over long periods. Popula­tions slowly diverge from one another due to differing selective pressures. The changes result in transi­tional forms that are seen in the fossil record.
Punctuated Equili­brium
Describes the pattern of long stable periods in which species stayed much the same. These periods were interr­upted by short periods in which the quick pace of evolution rapidly resulted in the formation of new species. The stimulus for evolution is a sudden signif­icant change in the enviro­nment.
The fossil record shows that rapid bursts of evolution have been often followed by mass extinction

The Main Point's of Darwin­'s Theory of Evolution

Overpr­odu­ction
Organisms have the capacity to produce more offspring than the enviro­nment can support.
Compet­ition
There is a struggle for resources among indivi­duals within a popula­tion.
Variation
There is a natural variation within popula­tions, meaning indivi­duals within a species are not identical.
Adaptation
Some variations provide advantages in the struggle of existence. Indivi­duals with beneficial traits are more likely to survive.
Natural Selection
Over time, the enviro­nment selects those variations that enhance an organi­sm's ability to survive and reproduce. This leads to accumu­lation of advant­ageous traits in a population over genera­tions.
Speciation
Over long periods, the accumu­lation of differ­ences through natural selection can lead to the formation of new species.
Variations in a species are the result of mutations in DNA. These mutations are the source of new alleles, the variations upon which natural selection can act.

It is important to remember that mutations are random in a popula­tion, and may produce a change in the phenotype of the organism.

Whether or not the mutation is beneficial or harmful depends on the enviro­nment.

Evolution then selects those organisms that are best adapted to their enviro­nment at the time

Types of Natural Selection

Stabil­izing Selection
Favours indivi­duals with an average value for a trait and selects against those with extreme variat­ions.
Direct­ional Selection
Favours indivi­duals possessing values for a trait at one extreme of the distri­bution and selects against the average and the other extreme.
Disruptive Selection
Favours indivi­duals at both extremes of the distri­bution and selects against the average.

Natural vs Artificial Selection

Both natural and artificial selection are mechanisms of change in the gene pool of a popula­tion. The key difference is that in artificial selection, humans ensure indivi­duals with the more desirable traits are allowed to reproduce. In natural selection, those indivi­duals who are best suited to their enviro­nment survive and reproduce.

Artificial Selection is a form of non-random mating, one of the causes of change to a gene pool.

Three Types of Adaptation

Behavi­oural
How organisms respond to their enviro­nment. Eg. Migration, Hibern­ation, Sunflowers bending towards light.
Physio­logical
Changes in an organi­sms­' metabolic process. Eg. Antibiotic Resistant Bacteria, Pesticide Resistant Insects.
Structural
Adapta­tions of a physical feature that will increase it's chance of survival. Eg. Whale blubber helps survive arctic waters, webbed feet help water fowl swim better.
2 Types of Structural Adaptation
Mimicry allows for a species to mimic another. The caterp­illar larva of the hawk-moth mimics a snake to fool birds.
Camouflage allows for a species to blend with the enviro­nment. Stick bugs look like tree branches. Tiger stripes help it blend in the jungle. Most species see orange as green instead which is why camouflage works.

Acclim­ati­zation is not natural selection because an organism becomes accustomed to new enviro­nmental condit­ions.

How can variation alter a gene pool?

Natural Selection
The better adapted indivi­duals survive and reproduce, passing their genes to the next successive genera­tions.
Immigr­ation and Emmigr­ation
Adding or removing indivi­duals from a population will affect allelic freque­ncies and therefore the gene flow.
Genetic Drift
The change in the gene pool due to random chance.
Non-random mating
Often the case as choice of mates is an important part of behaviour.
Mutations
Occurs consta­ntly. They provide the source of new alleles or variations upon which natural selection can take place.

Hardy-­Wei­nberg Principle Examples and Circul­ation

In a stable popula­tion, the frequency alleles in a population will equal to 1. This can be expressed as p+q=1 where:
p = the frequency of the dominant allele
q = the frequency of the recessive allele

The Hardy-­Wei­nberg Principle is also useful in explaining why genotypes within a population tend to remain the same, as well as for determ­ining the frequency of a recessive allele. The Hardy-­Wei­nberg Principle equation (p2+2pq+q2=1) allows to calculate the freque­ncies of the three genotypes where:

p2 = frequency of indivi­duals homozygous dominant
q2 = frequency of indivi­duals homozygous recessive
2pq = frequency of indivi­duals hetero­zygous

How to solve:
1- Convert % to decimal and solve for q or p
2- Using the equation 1-p=q or 1-q=p to solve for the unknown
3- Put in the newfound values of p and q in the equation
It should always add up to 1

Example:
A population of mice has a gene made of 90% M alleles (black fur) and 10% m alleles (grey fur).

q Recessive Allele = 0.1
p Dominant Allele = 0.9
q2 Homozygous Recessive = 0.12 = 0.01
p2 Homozygous Dominant = 0.92 = 0.81
2pq Hetero­zygous = 2(0.9*0.1) = 0.18

0.01+0.81­+0.18=1

Reprod­uct­ively Isolated Popula­tions

Speciation
Occurs when members of a popula­tions become reprod­uct­ively isolated from one another and can no longer produce fertile offspring with each other.
Geogra­phical Isolation (Allop­atric Specia­tion)
Occurs due to the formation of physical barriers that prevent gene flow between the two popula­tions. If the different popula­tions are subjected to different natural selection processes, allelic freque­ncies for genes will change. The two popula­tions become geneti­cally different that they become two separate species.
Niche Differ­ent­iation (Sympatric Specia­tion)
Occurs when the gene flow between members of a popula­tions is restricted due to ecological isolation. Some indivi­duals may be better and adapted to a slightly different habitat in an ecosystem and begin to specialize in that habitat.
Altera­tions in Behaviour
Should a group of nocturnal mammals become active during the day, they may no longer reproduce with their counte­rparts who are active at night.
Chromosome Mutations
A malfun­ction in meisosis that can lean to polyploidy in a plant. Because plants can reproduce asexually and self-p­oll­inate, then new polyploidy can reproduce, even though it is reprod­uct­ively isolated from its parents.
Polyploidy = (multiple copies of chromo­somes)

Allopatric vs Sympatric Speciation

Allopatric vs Sympatric Speciation

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