Mutations Flashcards
What are gene pools?
sum of all alleles in a population
Allele frequency
how many of each allele of a gene occur in the gene pool
What are Mutations? where can it occur
a change in the DNA that can affect a single gene (gene mutations) or all/part of a chromosome (chromosomal mutations)
- occur in body or sex cells
What are somatic mutations?
- occurs in body cells
- often involved in cancerous grwoths
- not inherited
What are germinal mutations?
- occur in gametes
- don’t usually affect individual but may be passed onto next generation
Two main types of mutations? and describe
- Gene mutations
- Changes in a single gene so that traits normally produced by that trait are changed.
- Occur during DNA replication - Chromosomal mutations
- all or part of a chromosome is affected.
What are causes of mutations?
- Agents known to increase rate of mutation called mutagenic agents or mutagens - called induced mutations
- Spontaneous mutations – random error in biological process-
What is a type of gene mutation?
Point mutation
What is point mutation?
- change in only one base that could alter a protein, have no effect at all, or prevent the protein being produced
- Within genes, the sequence of the bases in DNA is the code for amino acids used to build a protein.
- If DNA of particular gene is altered, the protein it codes for could be missing or abnormal.
What are the 3 mechanisms of point mutation?
- Inserted – new nucleotide added to DNA strand
- Substituted – existing nucleotide is replaced with a different base
- Deleted – a nucleotide is removed from the DNA strand
2 Examples of point mutation?
Albinism – mutation in gene for melanin production
- Effects: absence of pigment from hair, skin, eyes
Duchene muscular dystrophy – arises from mutation in mother which can be passed onto sons, or in male zygote
- Effects: wasting of leg muscles and later arms, shoulders and chest.
- Death occurs within failure of respiratory muscles
What is a Lethal recessive allele? what do they cause? and example
- Most gene mutations produce a recessive allele called Lethal Recessive
- They are recessive mutations which are lethal if not masked by dominant allele
- Cause death of embryo or foetus, or early death of child
- Eg. Tay Sachs Disease
What are chromosomal mutations?
Involve all or part of chromosome and affect a number of genes
- Cause abnormalities so severe, miscarriage often occurs in early pregnancy.
5 Types of chromosomal mutations
Deletion: part of chromosome lost
Duplication: section of chromosome occurs twice.
- Can happen when part of chromatid breaks off and joins to wrong chromatid.
Inversion: break occurs and broken piece joins back on wrong way around.
- Change order of gene and may disrupt pairing of homologous pairs in meiosis.
Translocation: part of chromosome breaks off and re-joined to wrong chromosome.
Non-disjunction: chromosome pair does not separate during meiosis and one daughter cell has extra chromosome while the other has one less.
- Aneuploidy – change in chromosome number
What are 3 examples of chromosmal mutation?
- Trisomy: three copies of a chromosome (three copies instead of two)
-eg Trisomy 21(Down Syndrome) - 3 of chromosome 21.
- Result of non-disjunction
- Intellectual disability, developmental delay
- Monosomy: individual missing a chromosome (one copy instead of two)
- eg Turner’s syndrome
- Monosomy X (and no Y chromosome)
- Females, short in stature, lack secondary sexual characteristics, infertile.
- Partial trisomy/monosomy: part of extra chromosome/part of one chromosome missing
- eg Cri-du-chat syndrome
- Partial monosomy
- Missing portion of chromosome 5
- Problem with larynx and nervous system
What is frameshift?
when bases have been added or removed -> can affect the outcome for all the DNA from that point on
What are the 4 mutations that can be classified by effect?
- Missesne mutations: cause a change in amino acid (and therefore, protein)
- Nonsense mutations: change in the base sequence to code STOP, stopping protein synthesis and producing protein unable to function
- Neutral mutations: cause change to amino acid, however, does not change the structure of protein enough to affect protein’s function
- Silent mutation: does not change the amino acid (or protein).
What is evolution?
- the change in characteristics of a species over time.
- It is gradual and occurs over a number of generations.
- reflects the changes in allele frequencies in populations, not individuals
Change in alleles present in a population may be due to…
- New alleles forming due to mutation or introduced due to migration
- Frequency of alleles changing due to selective pressures in natural selection or by chance in genetic drift.
3 Mechanims through which evolution occurs
Migration
Natural selection
Genetic drift
What is migration?
individuals moving between populations- enables gene flow
What is gene flow?
- movement of genetic material from one population to another.
- Individuals moving between populations (migration) enable gene flow.
What are barriers to gene flow and the types?
Barriers inhibit/hinder interbreeding between populations leading to separate gene pools forming.
- Barries classified by cause:
- Geographical barriers
- Sociocultural barriers:
What is Geographical barriers?
E.g. oceans, mountain ranges, deserts, expansive ice
Most common barrier for early humans.
E.g. First Nations people of Australia isolated by oceans as sea levels rose.
What is Sociocultural barriers?
developed as humans people more culturally complex
Language and religious groups, economic status, educational background and social position.
E.g. Basque people of Pyrenees (France & Spain) have unique language which has preserved culture and gene pool.
What is Natural Selection?
- the process by which a species becomes better adapted to its environment
- individuals with favourable characteristics have a survival advantage and pass characteristics to next generation
- there must be struggle for existence and those best suited to environment were more likely to survive (survival of the fittest).
- environmental factor acting is selective agent
What is sickle cell anaemia? how is it caused?
- an example of natural selection operating in human operations
- results when homozygous for a particular recessive allele of the HBB gene on Chromosome 11.
→Point mutation changes amino acid from glutamic acid to valine altering the shape of the haemoglobin molecule
What does sickle cell anaemia result in?
- Results in sickle-shaped (crescent) red blood cells which:
- Die early resulting in anaemia
- Are inflexible and can become stuck in blood vessels causing blockages.
- Complications include fatigue, jaundice, organ damage, high blood pressure, heart failure.
- Often fatal.
- found to provide resistance to malaria and therefore maintained in the gene pool in areas where malaria exists.
What are the 3 effects of sickle cell anaemia of allele frequency/gene pools?
- Heterozygotes for the sickle-cell trait were also found to be less susceptible to malaria and usually only affected by sickle-cell anaemia at low O2 conditions.
- Having only one sickle-cell allele provides individuals living in malaria-prone areas a survival advantage = heterozygote advantage.
- Presence of malaria acts as a selective agent.
What are the 3 basic observations the theory of natural selection based on?
- Variation: all members of a species vary and variation could be passed onto next generation.
- Birth rate: all living organisms reproduce at rate greater than food supply and other resources increase.
- Nature’s balance: although high birth rate, species numbers relatively constant.
6 Summary points of natural selection?
- There is variation of characteristics within a population
- More offspring are produced than can possibly survive to maturity
- Because of excessive birth rate and limited resources, there is struggle for existence (competition for survival).
- Individuals with characteristics best suited to environment have more chance of surviving and reproducing – survival of the fittest.
- Favourable characteristics are passed onto next generation.
- In gene pool, proportion of alleles that produce favourable characteristics gradually increase
2 Examples of Natural selection in humans
- Features of human body correlate well with environments they occur in:
- Long bodies and short limbs = smaller surface area for heat loss
-> Inuit people indigenous to Arctic regions - Short bodies and long limbs = larger surface area for heat loss.
->People in very hot parts of Africa.
What is Random genetic drift?
- The random non directional change in allele frequency between generations that occurs by chance
- allele that is rare in large populations can become frequent in small populations -> making it significant
Two types of genetic drift
- founder effect
- bottleneck effect
Founder effect
a small group (not representative of the original population) moves away from the homeland and establishes a community which later expands
- Because of size, chance can cause new groups to have:
- Different allele frequency
- Decreased genetic variation
Bottleneck effect
occurs when a large population is reduced in size and the alleles present in the new gene pool are random -> survival not due to a specific trait
What is Speciation
- the process of new species evolving
- not a mechanism for evolution, it can be a result of these changes (evolution) over a very long period of time.
Explain the 4 steps to speciation?
- Variation: a range of varations (Allele frequencies) exists within population, sharing a common gene pool
-Isolation: barrier has formed, diving population, no interbreeding occurs between two populations, each population has separate gene pool
- Selection: diff selection pressures act on populations over a no. of generations, changes gene frequencies of each gene pool, leaf to evolution of diff sub species
- Speciation: over a long period of time, change in gene frequencies may be great enough to prevent the production of fertile offspring between two populations = two species exist.
What is a fossil
- Any preserved trace left of an organism – including footprint, burrows, faeces, or impressions of all or part of animal or plant (e.g. teeth, bones, etc.)
- Usually bones, teeth or footprints in case of humans, artefacts
What are artefacts?
an object made or modified by humans
How are fossils formed?
- Parts of organisms buried by drifting sand, mud deposited by rivers, volcanic ash (not lava – too hot), collapsing caves, or other organisms.
- Rapid burial slows/prevents decay.
Where are fossils found?
- human ancestors often found at edges of ancient lakes and river systems, caves or in volcanically active areas
- cus the organism can be buried rapody, preventing devompsoiton.
- lakes and rivers build up sentiments when flooding occurs or when water low slows rapidly.
What are the 4 conditions requried for fossils to form?
- quick burial
- presence of hard body parts
- absence of bone decay
- long period of stability
Fossilisation of bone
- Wet, acidic soil dissolved bones - unless containing no oxygen (e.g. peat), then it may occur.
- Alkaline soil produces best fossils – minerals in bones not dissolved.
- New minerals (lime/iron oxide) deposited in pores petrifying it (turning to rock) while maintaining its structure.
What is dating of fossils and types?
- Dating: Determining the age of fossil/artefacts
Able to provide: - Absolute dates: actual age of specimen in years
- Relative dates: determine if one object older than another.
- Age of fossils given in years ‘before present time’ – e.g. 45 000 years BP.
4 Absolute dating fossils technqiues
- Potassium-argon technique
- Radiocarbon (carbon-14) dating
- Accelerator mass spectrometry (AMS) radiocarbon dating
- Dendrochronology (tree-ring dating)
What is an isotope
different forms of same element with different number of neurons
What is decay
emission of particle from nucleus
What is potassium argon technique?
based on decay of radioactive potassium to form calcium and argon
- radioactive potassium-40(isotope) decays to calcium-40 and argon-40
→occurs slowly but at a constant rate
- amounts of potassium-40 and argon-40 in rock used to determine age of rock
- suitable rocks 100 000 - 200 000 years or older
→ usually produced in volcanic eruptions
material used: volcanic deposits
What is radiocarbon dating?
based on decay of carbon-14 to nitrogen
- for every one carbon-14 atom, there is million million carbon-12 atoms
→ incorporated into plant tissue and then animal tissue when consumed
→ intake stops at death and then decays at fixed rate
- amount of radiation from sample measured to estimate carbon - 14 to carbon -12 radio and determine age
- Carbon dating cannot be used for samples older than 60 000 years – no carbon-14 left in sample.
What is Accelerator mass spectrometry (AMS) radiocarbon dating?
- more refined used to date smaller sample (~100 micrograms)
- Involves breaking sample into atoms so number of each carbon isotope can be counted.
- Became possible to date cave paintings accurately from tiny samples of pigment (made from charcoal, honey, milk, blood, seed oil, etc.)
- material used: carbon compounds
LIMITATIONS: - Carbon dating cannot be used for samples older than 60 000 years – no carbon-14 left in sample.
- Sample must contain organic matter
What is Dendrochronology
aka tree dating
- Concentric rings within a tree trunk examined – particular rings produced during exceptional weather conditions used as markers.
- By comparing living trees with timber taken from ancient human structures, dates of building can be determined.
- material used: wood
- dating can be used for samples that are up to 9000 yrs old
LIMITATIONS:
- Timber rarely preserved more than a few thousand years
2 relative dating techniques?
- Stratigraphy
- Fluorine dating
What are index fossils
common/widely distributed/only present at particular time -> used to compare strata in different locations
What is stratigraphy?
study of layers, or strata.
- principle of superposition: younger layers of rock at the top
- Correlation of strata: matches rocks in different areas by matching rock and fossils it contains.
- Fossilised pollen grain: can be used as index fossils and allow botanists to determine vegetation through time
What is fluorine dating?
- When bone is left in soil, fluoride ions from water and soil replace some of the ions in the bone.
- Older fossils will contain more fluoride.
- Concentration of fluoride varies between places so unable to determine absolute age
What are problems with the fossil record?
- correct conditions don’t always occur making fossils a chance occurrence
- small portion of fossils testing have been discovered
- dating fossils can be problematic
- unusual to find fossil of an entire organism -> often only a few fragments of bone
What are phylogenic trees?
- Represents Probable evolutionary relationships between organisms derived from common ancestor
- Ancestral organism forms ‘base’ of the tree and organisms which arise are placed on ends of ‘branches’.
- Closely related organisms are closer together.
- Useful for showing evolutionary pathways.
Biomedical evidence for evolution: Protein sequences
- by comparing the type and sequences of amino acids in a similar proteins from diff species, the degree of similarity can be established
- the degree of diff between proteins enables an estimate to made of the amount of evolution that has taken place since two species developed from common ancestor.
- longer the period of time, greater number of amino acids diff
What are ubiquitous proteins?
one of a group of proteins that appear to be in all species, called ubiquitin - present in all types of cells
- perform basic, essential tasks
- eg cytochrome C
