Biology U4 AOS1

Gene pool + allele frequency

Gene pool

• A gene pool is the collection of all the genes and alleles within a specific population

Allele frequency

• Allele frequencies refer to the proportion of a particular allele appearing at a certain gene locus in a gene pool

Mutations

• Mutations involve permanent changes to the DNA sequence

• They can occur either spontaneously or be induced

Mutation categories

• Mutations can be categorised as either

  • Point mutations - single nucleotide changes in a gene

  • Block mutations - changes to large sections of DNA

Types of mutations

Silent mutation

• A single base is substituted by another

• Called silent or neutral mutations and produce little or no change in the phenotype

 

Missense mutation

• A single base is substituted by another

• Usually results in coding for a new amino acid in the polypeptide chain

 

Nonsense mutation

• This results in a new triplet that does not code for an amino acid

• The resulting triplet may be an instruction to terminate the synthesis of the polypeptide chain

 

Reading frame shift

• A reading frame shift results in all new amino acids in the polypeptide chain from the point of insertion or deletion onwards

• The resulting protein will most likely be non-functional due to the change

Block mutations

• Block mutations involve changes to larger sections of DNA

• These alter the structure of a chromosome by deleting, duplicating, inverting or translocating sections of DNA

• This usually occurs during prophase I of meiosis

Aneuploids

• Aneuploidy refers to a chromosomal abnormality in which an organism possesses an incorrect number of total chromosomes caused by the addition or loss of an individual chromosome

• Examples include

  • Down syndrome, Klinefelter syndrome

Polyploidy

• Polyploidy refers to a chromosomal abnormality in which an organism has an incorrect number of sets of each chromosome - there is an entire set of chromosomes added or missing

• This can be common in plants, but is often fatal in animals

Evolutionary significance

• Mutations can create and introduce new alleles into a population, thereby increasing genetic diversity

• However, for the mutation to be heritable, it must occur in an individuals germline cells

• Most mutations are either neutral or harmful.

Enviromental selection pressures

Factors within the environment that influence the survivability of a species

• through these factors allele frequencies can change and the process of natural selection can occur

Natural selection steps

• Natural selection involves the selection of the phenotype most suited to overcome the environmental selection pressure

• Organisms more suited to an environment are said to have a higher fitness due to their advantageous phenotype(s)

• Over time, the fitter organisms have a selective advantage and are more likely to survive, reproduce, and pass their alleles on to the next generation, increasing the allele frequency of the advantageous phenotype

The effect of selection pressures

Enviromental selection pressures can reduce the genetic diversity of a gene pool

Advantageous traits will become more common in a population, and the allele frequencies shift in favour of these alleles

High + low genetic diversity

High genetic diversity

• The survivability of a species increases as large genetic diversity increases. The more variation, the higher the chance of individuals possesing favourable alleles that will help the population survive if there is a change in selection pressures.

Low genetic diversity

• Low genetic diversity can lead to the risk of extinction due to an inability to adapt to changing environmental selection pressures

  • When populations reduce, inbreeding becomes more common and disadvantageous phenotypes can result from usually hidden alleles

gene flow

Gene flow

• Gene flow is the movement of alleles from one population to another

• This occurs due to interbreeding because of immigration

  • occurs with close proximity populations / no more geographical barriers

Greg taylor

Shoots 3’s like a madman

Genetic drift

A change in populations allele frequencies due to sudden and random occurences

Why does genetic drift occur

Bottleneck effect

Founder effect

Bottleneck effect

• The bottleneck effect occurs when a large portion of a population of a population is wiped out by a random and sudden event, such as a natural disaster.

  • This results in reductions in population size, impacting allele frequencies

Founder effect

• The founder effect occurs when a small unrepresentative sample of individuals separates from a larger population to colonise a new region and start a new population

  • (think dale curtis going from bairnsdale to melbourne to shoot his load into sange and make the worst child of all time)

Gene flow on diversity

When individuals enter a population, their alleles are added to the gene pool of that population, increasing the diversity

The opposite happens when individuals emigrate out

Impact of genetic drift on small populations

Smaller populations are more susceptible to the effects of genetic drift, as they generally have a lower genetic diversity to begin with

Impact on genetic diversity - image summary

The risks of reduced diversity

Two major risks involves with reductions in genetic diversity include

• Inbreeding can occur, which can promote harmful alleles

• It can lower adaptive potential, so populations are more vunerable to selection pressures

Speciation

Speciation is the process by which populations genetically diverge until they become distinct species

There are two types of speciation:

• Allopatric speciation

• Sympatric speciation

Factors affecting speciation

Factors such as mutations, natural selection, selection pressures, genetic drift, and gene flow all influence the frequency of alleles within a population

• As genetic differences accumulate within populations, speciation can occur

Defining species

Individuals are recognised as different species when they can no longer interbreed with another to produce offspring that is viable (able to survive to maturity) and fertile (having the ability to produce offspring)

Allopatric speciation

involves the formation of a new species because of a geographical barrier

• these barriers prevent gene flow and allow genetic differences to accumulate due to exposure to different selection pressures

Sympatric speciation

involves the formation of a new species in populations located in the same region

• this occurs through selection pressures acting on different phenotypes causing a divergence from others and forming a new species

Example of speciation - Howea palms

• On Lord Howe Island there are two species of palms called Howea forsteriana and Howea belmoreana that shared a common ancestor

• It has been determined H. belmoreana inhabits neutral and acidic soils, whilst H. forsteriana inhabits more basic soils

• Soil pH impacts different flowering times

• This results in reproductive isolation where the flowering of the two species doesn’t occur at the same time and they don’t cross pollinate

• Over time differences accumulated and they could no longer interbreed to produce viable and fertile offspring

Sympatric speciation and polyploidy

Polyploidy can result in sympatric speciation as the new polyploid will have a different of chromosomes from the rest of the species

• This can result in reproductive isolation as the gametes may no longer be able to produce viable, fertile, offspring

Selective breeding

The process by which humans can select or remove traits from a population by directly controlling the breeding of the animal or plants

Selective breeding vs natural selection

Selective breeding shares similarities with natural selection including the requirement for variation, the presence of a selection pressure, and the heritability of the trait.

• The key differnece lies in the origin of the selection pressure

Selective breeding is human induced for a desired trait rather than enviromental

Effect on genetic diversity

• Selective breeding will reduce genetic diversity and overexpress deleterious alleles (through inbreeding), which can reduce adaptability and fitness within a population

• This can lead to a human-induced bottleneck effect, as only a small percentage of individuals naturally express traits desired by humans

Wild captive populations

Wild populations will maintain higher levels of genetic diversity and have higher adaptive potential compared to their captive bred populations

Antibiotics DEF

Antibiotics are medicines that treat bacterial infections

Resistence and natural selection

Antibiotic resistant bacteria forming is a result of the process of natural selection, where the exposure to antibiotics is the selection pressure

• Bacteria can exchange genetic material through bacterial conjugation, spreading the alleles for antibiotic resistance

Viral antigenic drift and shift

Viruses constantly adapt and modift their antigens through the process of antigenic drift and antigenic shift

• By changing their antigens, viruses can evade the adaptive immune system due to the specificity of immunological memory cells

Antigenic drift

occurs through small and gradual changes (mutations) in the genes encoding for viral surface antigens

• Initially, previous memory cells will be capable of recognising these mutated surface antigens but as mutations accumulate new viruses can form

Antigenic shift

Occurs through sudden and significant changes in the genes encoding for viral surface antigens

• This commonly occurs when two or more different strains of a virus combine when infecting the same host at the same time

  • natural immunity to new virus is unlikely making it more infectious

Fossil succession

The principle that one fossil succeeds another in a predictable order within the rock strata

• If the fossil is higher it is a newer fossil and was born after, if a fossil is lower it is an older fossil and was born before - this is known as relative dating

Fossilization process

• Death of an organism

• Burial and decomposition

  • Sediments covering the organism protects it from scavengers and slows decomposition due to a lack of light, O2 and H2O

• Petrification

  • Hard material (e.g. bones and teeth) remain and form into the fossil

• Exposure

  • Uplift or erosion brings the fossil to the earths surface

Types of fossils

• Body fossil

  • the actual body parts of the plant or animal

 

• Permineralized fossil

  • When groundwater deposits minerals into the organic spaces turning them into stone

 

• Mould and cast fossil

  • A mould is when a hollow is formed in sediment after an organism decays away, a cast can then form if this hollow is filled with minerals

Trace fossils

Indirect evidence of behaviour such as nests, footprints, teeth marks, and burrows

• Insights into behaviour being analysed

Index fossils

fossils used for relative dating as they are known to have only existed for some time

• If a target fossil is found in the same strata as the index, an estimated range of age can be determined from that fossil

Transitional fossils

Transitional fossils are intermediaries between an ancesteral species and its descendant species

• They exhibit traits common to both groups, so they can provide evidence to the evolution of the descendant species

Dating fossils

To date fossils is to determine the age of them using two seperate techniques

• relative dating

  • absolute dating

Relative dating

Using the law of fossil succession, we can asign a relative age based on the position of the fossil compared other fossils

Absolute dating

gives a more exact age of the fossil

radioactive dating is used

• this involves comparing the ratio of radioactive isotopes found inside the fossil to the relatively stable amount found in the atmosphere

Radiocarbon dating steps

• All living things contain carbon

• This carbon exists as a ratio of two isotopes - 12C (a stable isotope) and 14C (a radioactive isotope)

• The ratio of these two isotopes will be the same as the ratio in the atmosphere, given that carbon is constantly being cycled between the organism and its environment while it is alive

• Because your not getting any new carbon your carbon 14 will decay, this is then measured and compared to the environment to figure out how old the fossil is

• When the organism dies, its 14C will begin to decay and breaks down into 14N (a stable isotope)

• While this decay occurs, the carbon in the dead organism will not be replaced by existing carbon in the atmosphere

• So levels of 12C will remain the same, while 14C decays at a known rate - causing the ratio between the two isotopes to change

Pros and cons of carbon dating

Pros	Cons
Its better than relative dating as it gives an exact age in years	It has a limited time range and cant be used for fossils older than about 50,000 years
It is very effective for dating anything that was once living e.g. bone, wood, charcoal	Does not work on non-living
It is very reliable as the decay predictions	Easy to contaminate

Structural morphology

One method to assess relatedness is through structural morphology, which involves looking for similarities between the physical features of different species

• this can be in the form of homologous and vestical structures

Homologous structures

Features found in different species that may look and function differently from one another but are derived from a common ancestor

• Similar structure → different function (gives evidece of relatedness)

Vestigal structures

structures found within organisms that once served a purpose for their ancestors but due to changing selection pressures have lost their original function and arent required anymore

• e.g.

  • The tail bone in humans

Molecular homology - amino acids

there are many common proteins found in different species, when analysed the amino acid shows differences

• The fewer differences provides an indication that these species are more closely related to eachother

DNA sequence similarity

DNA sequences can also be used to determine the relatedness between different organisms

• Just like amino acid sequences, a higher similarity in DNA sequence implies a closer level of relatedness between different organisms

Benefits and limitations of molecular homology

Phylogenetic trees

A diagram that shows the evolutionary relationships between different species

Interpreting phylogenetic trees

• Phylogenetic trees can be read backwards to determine the most closely related species to a particular taxonomic group

• For example, you can trace back from the human line to reach node A, which splits humans from monkeys, showing that monkeys are the closest relative to humans on this tree

 Further back, node B separates humans and monkeys from dolphins and sheep, showing that humans are more closely related to monkeys than they are to dolphins and sheep

• Its important to note that the most recent common ancestor of humans and monkeys occurs at node A

Other features (reference image)

• The lack of a node between species (E.g. Y and Z) means that the exact divergence point is unknown (due to lack of fossil or molecular evidence)

• A break between species (e.g. W and X), means that W is possibly an ancestor of X but there is no evidence of transitional fossils between the two species to support this hypothesis

• The branch with species S does not reach the end of the tree, indicating that it is extinct

• Nodes usually only split into two lineages, but sometimes they can split into three or more (e.g. T, U, and V)

• This means that it is unclear which species diverged from the others first

• This occurs if there is insufficient data or if two speciation events occurred closely together

exchange of genetic material

Sometimes genetic material is passed between groups after they have diverged

for example, there is strong evidence that groups of humans interbred with neanderthals causing parts of their genomes to be passed around

Taxonomy

a system used to categorise all living organisms based on shared charecteristics and evolutionary relationships

• Domain

• Kingdom

• Phylum

• Class

• Order

• Family

• Genus

• Species

remember

(Dumb Kids Playing Catch On Highways Get Squashed)

Human taxonomy

The only categories required are mammals, primates, hominoids, hominins

• Mammals all have mammary glands, hair or fur and three middle ear bones

• Primates have grasping hands, stereoscopic vision and large complex brains

Charecteristics of primates

• 3D colour vision and forward facing binoculars eyes

• A large number of touch receptors in the hands

• A large cranium relative to body weight

Grasping hands and feet

• Hands and feet can be described as prehensile if they grasp and hold objects

• Fully opposable refers to the ability to move the thumb to freely touch the tip of the other fingers

• Power grips wrap around and hold tightly while precision grips use fingertips to pick up and hold small objects

Hominoids

within the order of primates, humans are further classified into the superfamily hominoids

species belonging to this group are called hominoids (or apes) and include:

• Great apes - orangutans, chimpanzees gorillas and humans

• Lesser apes - many different species of gibbons

Charecteristics of hominoids

• Have no tail

• Increased cranium size

• Y5 pattern on lower haw molars

• Broader rib cage

The key characteristics of hominins

• Bipedal locomotion

• Increased brain size

• Smaller teeth than other primates

• Highly developed hands with fully opposable thumbs

Applications for bipedalism

• Centralised foramen magnum - allows skull to balance on spine

• S-shaped curvature of the spine - provides shock absorbance and maintains centre of gravity

• Bowl-shaped pelvis - supports organs

• Valgus angle of the femur bone - centres knees under body

• Foot arch with non-grasping aligned big toe - allows for spring and forward thrust

Advantages of bipedalism

• Very energy efficient for long distance travel

• Carrying tools, infants, food etc while moving

• Better thermal regulation

Disadvantages of bipedalismCirculatory issues

• Circulatory issues

• Childbirth complications