VCE Biology UNIT 4 NOTES PDF

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VCE Biology UNIT 4 NOTES...

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Changes in the genetic makeup of a population KDP - the qualitative treatment of the causes of changing allele frequencies in a population’s gene pool including types of mutations (point, frameshift, block) as a source of new alleles, chromosomal abnormalities (aneuploidy and polyploidy), environmental selection pressures on phenotypes as the mechanism for natural selection, gene flow, and genetic drift (bottleneck and founder effects) and the biological consequences of such changes in terms of increased or reduced genetic diversity KDP - processes of evolution including through the action of mutations and different selection pressures on a fragmented population and subsequent isolating mechanisms (allopatric speciation) that prevent gene flow KDP - the manipulation of gene pools through selective breeding programs.

Causes of change in allele frequencies in a population’s gene pool Gene  a sequence of DNA nucleotides that code for a particular trait o Variation in a gene (i.e. allele) results in different forms of a particular trait o Variation is caused by random mutations in DNA and is enhanced in a species through sexual reproduction Phenotype  observable trait in a species – phenotype = genotype x environment o Monogenic trait  phenotype controlled by one gene o Results in discontinuous (limited/discrete) variation of a trait in a species (i.e. no. of fingers, ability to roll tongue) o Polygenic trait  phenotype controlled by more than one gene – genes involved are typically located on different chromosomes and are known as polygenes o Results in continuous (increased) variation of a trait in a species (i.e. hair colour, skin colour, height) Genotype  Allele combination of an individual Population  a group of organisms if the same species, living in the same place at the same time Gene pool  the sum of alleles possessed by an entire population which may be potentially passed onto the next generation Allele frequency - the relative proportion of a particular allele in a population – it is calculated through:

allele frequency=

2 ( no . of homozygotes) +(no . of heterozygotes ) 2 (total no . of individuals )

Mutations Definition: changes in DNA O Mutations create new alleles and causing variation in a population – variation can also be a result of different allele combinations during sexual reproduction o Mutations can occur randomly during replication or as a result of mutagens (factors that induce mutation – e.g. heat, X radiation, gamma radiation, UV radiation) O Mutations can be: o Neutral – have no effect on survival o Beneficial – increase the likelihood of survival o Harmful – decrease the likelihood of survival o Somatic mutations – occur in body cells and only affect that individual o Germline mutations – heritable as they affect gametes and can therefore be passed to the offspring

Point mutations Definition: A mutation that substitutes a single nucleotide from a sequence of DNA or RNA for another nucleotide - typically only affect a single gene Substitution mutations O A point mutation in which one nucleotide is replaced by another type of nucleotide Three types of substitution mutations: o Silent mutations – substitution results in a new codon that still codes for the same amino acid – occurs due to the degenerate nature of the genetic code  will not have any effect on the final polypeptide

o

Missense mutations – substitution results in amino acid replacement  still produce a protein but whether this protein can function properly or not is dependent on the importance of the amino acid that was replaced

o

Nonsense mutations – substitution results in the creation of a stop codon (UUA, UAG or UGA)  no other amino acid will be added after this point so this mutation can have severe effects, particularly if the mutation occurs early in the sequence

Frameshift mutations Definition: A mutation in which one or two nucleotides are either added or removed from a nucleotide sequence altering the codon sequence and reading frame Nucleotide insertion Results frameshift mutation in which one or two new nucleotides are added into the sequence pushing the rest of the nucleotides more back one or two places

Nucleotide deletion A type of frameshift mutation in which one or two nucleotides are removed from the sequence pulling all of the following nucleotides forwards by one or two places

Block mutations Definition: Mutations that affect large sections of a chromosome (i.e. multiple genes) – AKA chromosomal mutations O Usually occur during meiosis in eukaryotic cells O Can also be caused by mutagens Duplication mutations O Involve the replication of a section of a chromosome that results in multiple copies of the same gene on that chromosome Deletion mutations O Removes sections of a chromosome which leads to disrupted or missing genes o Can have serious effects on growth and development Inversion mutations O A section or sequence breaks off, rotates 180 degrees and reattaches to the same chromosome Insertion mutations O Occurs when a section of one chromosome breaks off and attaches to a different chromosome O Effects of this mutation depend on whether the cell retains two copies of every gene o during meiosis if the chromosome now containing the insertion is separated from the chromosome in which the material originated, some gametes may have two copies of the same gene whilst others may be missing them entirely. Translocation mutations O A whole chromosome or a segment of a chromosome becomes attached to or exchanged with another chromosome or segment - i.e. two non-homologous chromosomes may break off and at the same time and may reattach to the other chromosome, swapping genetic material

Chromosomal Abnormalities Definition: when a mutation involves whole chromosomes or a number of chromosomes Detected by looking at the karyotype

Aneuploidy Definition: cell or individual has more or fewer than two copies of a particular chromosome O Caused by non-disjunction during meiosis o Non-disjunction  two homologous chromosomes do not separate during the first division of meiosis – results in gametes with an incorrect haploid number and consequently an abnormal diploid number O Examples – o Klinefelter’s syndrome – XXY o Turner syndrome – XO

Polyploidy Definition: condition in which individual has more than two chromosomes in each set O Normal somatic cells are diploid (two complete sets of chromosomes) o during fertilisation when gamete cells (haploid) are supposed to come together to form a diploid zygote

O O

Polypoid cells can also arise due to problems during mitosis More common in plants over animals – human polyploid zygotes usually die

Natural selection Definition: when environmental selection pressures affect allele frequency in a population by selecting for advantageous traits, allowing them to survive and reproduce offspring who also possess these traits Environmental selection pressures  living and non-living factors that select ‘for’ or ‘against’ particular phenotypes in a species, increasing or decreasing the chances of survive and reproduce for organisms who possess these traits o climate conditions – i.e. temperature changes o competition for resources – i.e. food, water and shelter o mate availability o predatory abundance Templates to answer natural selection questions 1. Variation existed in species X, regarding trait Y 2. Trait Y was heritable 3. Selection pressure Z caused a struggle for survival amongst species X 4. Individuals that possessed trait Y” had a selective advantage, so they survived and reproduced passing on their favourable traits to the next generation 5. Over time the frequency of Y” increases in the population whilst the unfavourable trait decrease in frequency IMPORTANT THINGS TO NOTE –  Selection pressure determines which phenotypes make organisms ‘fitter’ and, consequently, which traits will be better represented in the next generation  Evolution occurs as a result of advantageous phenotypes becoming more common in a population which changes the genetic makeup of the population  Species with large amounts of genetic variation are less likely to go extinct  Species with more variation in alleles has a higher chance of possessing a favourable genetic trait that will help it survive if a new selection pressure arises

Gene flow Definition: the introduction and removal of alleles from a population due to migration o Immigrants may add new alleles to the gene pool whilst emigrants may remove/decrease the frequency of particular alleles in the gene pool O Gene flow can increase or decrease variation in a population by introducing and removing alleles O When gene flow exists between two populations their gene pool remains fairly similar O When gene flow does not exist between two populations, the gene pool is said to be isolated

Genetic drift Definition: unpredictable and random changes in allele frequencies in a population as a result of chance events O In small populations with little to no gene flow, genetic drift can result in the loss of alleles from the gene pool, causing – genetic drift is more noticeable in small populations

Bottleneck effect Definition: Genetic drift that occurs when the population drastically and quickly reduces as a result of a random event (i.e. natural disaster or human hunting) such that the phenotypes of the surviving population are not representative of the original population o phenotypes of individuals do not increase chances of survival and the individuals that survive will do so by chance O The bottleneck effect describes the impact on the remaining population

O

Reduced population size  reduced variation and increased number of homozygous individuals  more vulnerable to environmental change

Founder effect Definition: Genetic drift that occurs when a small population of individuals from a parent population colonise a new area and their phenotypes are not representative of the original population O Founding population does not represent the allele frequency of the original population = increased inbreeding = less variation O In the new environment, the selection pressures on the founder population are likely to be different from those experiences by the original population – drives changes in allele frequencies and causes evolution of species

Impact of the Founder effect and Bottleneck effect Small population with a limited gene pool and low genetic variation results in O Increased inbreeding, O Lower adaptive potential and increased vulnerability to new selection pressures Can be overcome by introducing new members to the isolated population in order to increase gene pool and variation Small populations are more likely to experience the negative effects of inbreeding and lower adaptive potential O

O O

Processes of evolution Evolution  the change in the genetic composition of populations overtime Species  a group of individuals that can mate and produce viable/fertile offspring Speciation  the evolution of a new species from an ancestral species o The new species is genetically different from the ancestral species that it can no longer interbreed and produce viable and fertile offspring

Allopatric speciation Definition: the evolution of a new species when an population becomes divided by a geographical barrier Steps:

1. Original species is divided by a geographic barrier (i.e. mountain range, desert, ocean etc.) into two isolated populations resulting in no gene flow between them 2. Isolated populations experience different selection pressures 3. Different mutations accumulate 4. Overtime, differences accumulate in each group and the two populations evolve into different species which, if reintroduced, would either not be able to interbreed or will not produce viable and fertile offspring after interbreeding as they have become reproductively isolated ISOLATING MECHANISMS: Prezygotic isolating mechanisms o Geographic isolation – separated by geographic features o Temporal mechanisms - differences in reproductive seasons o Morphological mechanisms - Differences in structure of genitalia o Behavioural mechanisms - different courtship patterns o Gametic isolation (chemical differences in gametes that prevent fertilisation) Postzygotic barriers o Zygote mortality – gametes do not survive o Hybrid sterility – infertile offspring O Allopatric speciation is a source for divergent evolution

Human manipulation of gene pools Selective breeding Definition – humans select desired traits and deliberately interbreed organisms that possess these traits to increase their frequency in the gene pool Selecting for the trait you want – 1. Variation in phenotypes must exist within population 2. Phenotypes must be heritable 3. Humans determine the desired trait and alter the breeding population 4. Interbreed parents who show desired trait either naturally or through human induced breeding 5. Continue this process until the allele frequency of the desired trait increases in the gene pool and the population reliably reproduces desired trait

Advantages of selective breeding. O O

Agricultural plants are usually selectively bred for high yield and high resistance to disease Animals are selectively bred to produce high quality products (i.e. wool or milk) or for personality traits (i.e. loyalty in pets)

Disadvantages of selective breeding O O O

Reduces resistance to environmental change due to decreased genetic variation in the gene pool Reduces biodiversity Can increase genetic abnormalities due to inbreeding of a small gene pool, increasing the likelihood of a homozygous recessive conditions

Changes in biodiversity KDP - significant changes in life forms in Earth’s geological history including the rise of multicellular organisms, animals on land, the first flowering plants and mammals KDP - evidence of biological change over time including from palaeontology (the fossil record, the relative and absolute dating of fossils, types of fossils and the steps in fossilisation), biogeography, developmental biology and structural morphology KDP patterns of biological change over geological time including divergent evolution, convergent evolution and mass extinctions.

Earth’s geological history and changes in life forms F.A.R.M – Fish  Amphibians  reptiles  mammals 3.5 bya Earliest known bacteria

Evidence for evolution Palaeontology Definition: the study of ancient life represented by fossils O Fossils  preserved remains, impressions or traces of organisms that provide evidence for its presence o May be preserved in rocks, amber, coal deposits, ice or soil o Provide information about the appearance, habitat, age and behaviours of organisms  Transitional fossils  fossils with features intermediate between those of ancestral and descendant species  Living fossils  living organisms that have remained essentially unchanged from their ancestors

Steps in fossilisation 1. Death of organism 2. Rapid burial of remains by being covered in sediment o Causes decay of soft tissue 3. Hard body structures remain, and mineralisation occurs o Occurs through dehydration, extreme cold, high acidity or absence of oxygen 4. Sediment layers accumulate and resultant pressure forms sedimentary rock 5. Earths movements raise the layers of the rocks to the surface 6. Rock erodes, exposing fossilised body structures

Conditions that reduce the rate of decomposition and increase an organism’s chance of becoming fossilised are: O areas of rapid sediment accumulation These kinds of conditions are O constant cool temperatures usually found underwater, hence O low light availability why a lot of fossil are found O physical protection from scavengers and decomposers (e.g. fungi, bacteria

Types of fossils Type of fossil Impression fossils

Description O Left when the entire organism decays but the shape or impression of the external or internal surface remains o Cast fossil  When the vacant space of an impression fossil is filled with a foreign material to form a three-dimensional sculpture

Permineralized fossils

O O

Trace fossils

O

Mummified organisms

O

When minerals (i.e. opal, pyrite, silica) replace the spaces in the structures of organisms Minerals may eventually replace the entire organism leaving replica of original fossil – known as petrification/mineralisation Preserved evidence of animal’s activity or behaviour, without containing any parts of the organism (i.e. footprints, casts of burrows, fossilised faeces) Organisms that have been trapped in a substance under conditions that reduce decay and so are changed little

Dating fossils Relative dating O Gives an approximate age of a fossil by comparing it to the known absolute age layers of sedimentary rock surrounding layer in which the fossil is found or with an index fossil O Relative dating assumes that the rock layers are laid down in order of formation – the bottom being the oldest and the top being the youngest

Absolute dating O Provides a more precise estimate of age for the fossil in comparison to relative dating Radiometric dating O Uses the proportion of radioactive isotopes present within rocks around the fossil or within the fossil to determine the age of the fossil O Isotopes decay into different elements at a known and constant rate o Half-life  the time it takes for the concentration of a substance to fall to half of its initial value Example – Radiocarbon dating O Carbon-14 decays to Nitrogen-14 and has a half-life of 5,730 years. O When an organism dies, the proportion of carbon-14 in its cells is the same as the proportion in the atmosphere o If one-eighth of carbon-14 remains when the fossil is found, the fossil has existed for three halflives 1 o

1 2



1 4



1 8

As one half-life is 5,730 years, the fossil has existed for 17190 years

O

O O

can be used 4 billion years old. Uranium can be used for samples less than 350,000 years old. Carbon can be used for samples less than12,000 years old.

Potassium/Argon for samples up to

Electron Spin resonance (ESR) O Buried objects (bone, teeth) are exposed to radiation from the soil – if these objects contain minerals, some electrons move to and remain in a high energy state (the longer the material has been buried the higher the number of electrons in a high energy state) O When such material is exposed to heat, the electrons return to a ground state O ESR is used at this time to estimate the time at which the material was last heated (i.e. when a tooth came into contact with the sun) Thermoluminescence O Involves determining the time elapsed since the material containing crystalline minerals (ceramics, lava) was either heated or exposed to sunlight O Time elapsed is calculated by measuring an accumulated radiation dose - as material is heated, a weak light is emitted proportional to the radiation dose absorbed by the material

Biogeography Definition: the study of the distribution of organisms O The continents of the world are positioned on plate tectonics which are in constant movement – continental drift o Pangea  Laurasia (north) and Gondwana (south)  Laurasia and Gondwana further split into other continents o The rate at which the tectonic plates are moving can be used to determine the point at which the land masses were joined

O O

Continental drift explains why fossils of the same species were found on entirely separate continents when no obvious migration existed As Pangea fragmented, oceans formed barriers and species split into isolated populations, eventually evolving into new species

Structural morphology Definition: the study of the form and structure of organisms Explanation Homologou Structures in diffe...