Biology: Module 6 - Genetic Change

what are two types of ways mutations are formed?

spontaneous or induced

what is mutagenesis?

process of inducing mutagens

what are the three types of mutagens?

chemical, naturally occuring, physical

what are chemical mutagens?

chemicals that cause mutations if cells are exposed for large periods of time

what is the effect of chemical mutagens?

inserts incorrect nucleotides (mispairing) —> changes DNA —> changes function of proteins.

what are examples of chemical mutagens?

ingested: alcohol, tar

environmental: benzene, asbestos

what are naturally occuring mutagens?

present at normal levels within natural environments and may cause mutations

what does naturally occuring mutagens effect?

change the function of genes —> can reduce efficiency of DNA repair systems

examples of naturally occuring mutagens?

hepatitis B, HIV, mercury, cadmium

what is physical mutagens?

includes heat and ionising radiation

what is radiation

transfer of energy through space from a source

what is ionising radiation

harmful radiation that has enough energy to break chemical bonds in molecules (DNA)

when ionising radiation breaks DNA what are some effects of that:

causes deletions, chromosome loss, rearranging DNA sequences, crosslinking of DNA, disturbs cell division, cell metabolism

what is electromagnetic radiation

short wavelengths with high ionising energy —> split electrons that causes damage in cells

what is the effect UV radiation

produces pyrimidine dimers (cross-linked nucleotides) that prevents nucleotides from pairing with complementary bases —> ends the strand prematurely —> affects cell cycle and gene products

what are pyrimidine dimers?

•  adjacent pair of bases on the same strand become attached to each other 

what is the relationship between wavelength and ionising energy?

increasing ionising energy means shorter wavelengths

list the waves in increasing frequency:

radio waves, microwaves, infrared, visible, UV, X-rays, gamma rays

give some examples of physical mutagens

Electromagnetic Radiation: radio waves, gamma rays

Ultraviolet Radiation: UVA, UVB

Artificial: radioactive material, atomic bombs, nuclear power, X-rays

what is UVA’s effect

more related to ageing rather than mutagenic and carcinogenic

what is UVB’s and UVC’s effect?

have shorter wavelengths so are higher in ionising energy

is mutagenic and carcinogenic

what are the two types of DNA repair mechanisms?

1. nucleotide excision repair

2. mismatch repair

what is nucleotide excision repair

a damaged or incorrect base pair is removed by a nuclease enzyme and replaced

what is mismatch repair

once DNA has replicated, DNA polymerase carries out a spell check for accuracy of replication

what is good mutations

creates new alleles that benefit an organism

what are bad mutations

affect the survival of organisms

can neutral alleles change?

have a fixed frequency unless gene flow or genetic drift occurs

why are mutations important?

mutation creates new alleles → creates variation → necessary for evolution

what two genes lead to cancer if mutated?

1. Proto Oncogenes

2. Tumour Suppressor Genes

what are proto oncogenes

code for proteins that stimulate cell cycle, promote cell growth

what are tumour suppressor genes?

code for proteins that repress cell cycle progression —> promote apoptosis (cell death)

what is cancer

uncontrolled cell division

what are spontaneous mutations

arise randomly from an error within natural process of DNA replication

what are induced mutations?

arose from environmental agents (chemical/radiation) that increases the change of nucleotide sequences being changed

what are point mutations

changes a single base pair of DNA - only affects a single gene (gene mutation)

what are chromosomal mutations

moves whole blocks or genes to different parts of a chromosome —> changes a series of bases = several genes

what is the effect of chromosomal mutations?

overall chromosome structure changes or the number of chromosomes in a cell changes

what is the affect of mutation on DNA

nucleotide base may be substituted, deleted, inserted

change change one amino acid or none

what is frameshift mutation

a type of point mutation that causes all subsequent codons to be read wrong

includes insertion and deletion

what are types of point mutations

substitution, frameshift (includes insertion, deletion)

what are three types of point mutation effects?

1. nonsense mutations

2. silent mutations

3. missense mutations

what are nonsense mutations

changes an amino acid to a stop codon

what are silent mutations

changes in DNA sequence that doesn’t change an amino acid

what are missense mutations

1. non-conservative missense: results in a different amino acid with a different type (basic or polar)

   1. conservative missense: results in a different amino acid with the same type as the original amino acid

what are the 4 types of chromosomal mutations

1. deletion

2. duplication

3. inversion

4. translocation

what is deletion in chromosomal mutations?

• Removal of sections of DNA 

• Reduces the gene number

• Cause: high heat, viruses, radiation

what is duplication in chromosomal mutations?

• Portion of DNA is duplicated/inserted → increases total number of genes

  • Location of duplication (intron/exon) and number of repeats → determines phenotypic effect

what is inversion in chromosomal mutation?

• When a section of DNA is removed, turned around 180^o , and reinserted into the chromosome 

• The bases are in reverse order

• E.g. haemophilia

what is translocation in chromosomal mutation?

• When a section of DNA is moved from one chromosome to a non-homologous chromosome

• Leads to gene fusion → region joins two normally separate genes

• Some scientists think transposons (transposable elements) inserted into DNA millions of years ago = making up a large portion of non-coding DNA

what is aneuploidy

a chromosomal abnormality when 1 or more copies of an entire chromosome are made or an entire chromosome is missing

when is aneuploidy caused?

usually by non-disjunction (in anaphase) during meiosis I or II

what is an example of aneuploidy?

• Trisomy 21 → 3 copies of 21st chromosome = Down’s Syndrome

what is polyploidy?

Def. contains more than two full sets of chromosomes

what is the difference between polyploidy and aneuploidy?

how does mutations affect organisms?

the type of cells where mutations occur determine the extent of the effect

what are germline mutations?

Germline mutations (in gametes) 

• A mutation occurs in the cells that produce gametes → appears in gametes

• Passed onto every cell in the offspring formed from that gamete 

  • The offsprings gametes will have it too

what are somatic mutations? its cause? its result?

Somatic Mutations (rest of body)

• Cause: DNA replication errors prior to mitosis

  • Spontaneous mutations may occur in the S phase of the cell cycle → go unrepaired by the cell → will go to the daughter cells through mitosis

• May result in an observable phenotypic difference e.g skin cancer

• May lead to a localised effect (e.g tumour) → NOT heritable

what is coding DNA

• DNA transcribed into mRNA → translated into amino acid sequences → forms proteins

is prokaryotes DNA mainly non-coding or coding?

• Prokaryotes’ DNA is mainly coding DNA

  • Many genes are responsible for DNA repair enzymes to maintain the DNA

  • If these genes are deactivated → prokaryotes have an ⬆ in the rate of mutation

  • (same for eukaryotes)

what is the importance of coding DNA

an organism’s phenotype is dependent on the direct result of the coding DNA

what is the effect of mutations on coding DNA

• Proteins aren’t produced  or Proteins aren’t produced properly → effect of that protein on the organism is changed

• Mutations that occur on the tumour suppressor genes → cancer (gene for suppressing mitosis is deactivated)

examples of mutated coding DNA?

E.g. mutated BRCA1 and BRCA2 genes can lead to breast or prostate cancer

E.g. Xeroderma Pigmentosum (XP): recessive genetic disease 

• Without XP → DNA repair enzymes work → fix damaged DNA

• With XP → DNA repair enzymes don’t work → damaged DNA doesn’t get fix → can lead to cancer

• XP → more susceptible to UV damage → skin cancer

what is non-coding DNA

• DNA which does not result in a direct protein product (polypeptide) 

  • Can be important as acting as a buffer to separate genes → if mutation occurs it won’t affect coding DNA

what are the roles of non-coding DNA? (sting)

satellite DNA: repeating sequences

telomeres: repetitive DNA at the end of chromosomes

introns: non-coding sequences within genes

non-coding RNA genes (e.g. tRNA)

gene regulatory sequences (sequences involved in transcription: promoters, enhancers, silencers)

what are enhancers

increase the frequency of gene expression by attaching proteins that help turn on particular genes

what is the effect of mutations on non-coding DNA?

• Changes gene expression (light switch 💡)

  • Mutation can turn on a gene → causes a protein to produced at the wrong point

  • Can close a gene → eliminates the production of necessary proteins

  • Have NO effect

what are some examples of non-coding DNA mutation?

• E.g. isolated pierre robin sequence

  • Caused by changes in non-coding DNA → changes the enhancer elements (SOX9 gene)

  • SOX9 is important in embryonic development

• E.g. Lactose Tolerance: 

  • Mutation is in lactase enhancer region → causes a binding site for transcription factors

  • Lactase gene is constantly expressed → allows adults to consume lactase

what are the causes of genetic variation (3)

1. fertilisation

2. meiosis

3. mutation

what is fertilisation and its sources of variation?

(Def.) 2 gametes fuse together to form a zygote

sources of variation:

Requires 2 gametes, infinite number of combinations

Random, equal probability

Dominant and recessive interaction

what id the definition of meiosis and its sources of variation

Gamete production as parent cells divide into 4 haploid daughter cells

sources of variation:

• Random mutations during DNA replication or during separation/disjunction of chromosomes

• Crossing over, combinations of alleles - prophase I

• Random segregation (corresponding alleles), anaphase I & II (in meiosis)

• Independent assortment (non-corresponding alleles), anaphase I & II

what is the definition of mutation and its sources of variation

(Def.) A permanent change to an organism’s DNA sequence

sources of variation:

• Introduction of new alleles

• Missense, nonsense, silence

what are the 5 factors of mutation on population

1. selective pressure

2. sexual selection

3. mutation

4. genetic drift (more obvious in smaller populations)

5. gene flow (more obvious in larger populations)

what is selective pressure, the reasons alleles change and its effect on the next generation?

Selective Pressure

natural selection

Variations that are passed on = individuals are more likely to survive

Alleles that make individuals more likely to survive become most frequent

what is sexual selection, the reasons alleles change and its effect on the next generation?

Certain individuals more attractive to mate - more likely to breed

Non-random mating

Alleles of attractive individuals are more common

what is mutation, the reasons alleles change and its effect on the next generation?

New genes arise due to errors in DNA replication

New alleles arise during gametogenesis

New alleles that are beneficial are frequent

what is genetic drift, the reasons alleles change and its effect on the next generation?

Random events (e.g. tornado) lead to a change in gene frequency because some indiv are dead

Random chance (non-selective)

Individuals within a population to be different because they were lucky

what is gene flow, the reasons alleles change and its effect on the next generation?

Indiv with different genes come into a population and spread their alleles

Mix with genetically different individuals (immigration/emigration)

Allele frequency in population changes

what is the definition of biotechnology?

use of biological organisms, their products or their processes to make new products that are useful to humans in areas (industry, agriculture, medicine)

what is ancient biotechnology and its features? (before 1800s)

Relied on observation, trial-and-error No actual understanding of genetics

Food Production of bread, cheese, alcohol  Selective breeding in crops and livestock for drought resistance, higher milk production Medicine: mostly natural plants etc.

what is classical biotechnology (1800s - 1950s) and its features

More systematic approach, used microbiology and chemistry to refine techniques

Pasteurisation/Fermentation: heating liquids to kill harmful bacteria, while maintaining nutrients Plant selective breeding: hybridisation and artificial pollination Medicine + Antibodies

what is modern biotechnology and its features?

Modern (1952  - today) 1952 - discovery of DNA

Direct genetic manipulation, very advanced understanding of genetics/reproduction

Genetically Modified Organisms: direct alteration to an organism’s DNA to produce more efficient organism/food CRISPR: enables precise gene editing that offers potential cures for genetic diseases

what ethical frameworks are biotechnologies deemed ethical from?

1. Utilitarianism: greatest amount of good for most people

2. Rights: people have the right to choose

3. Fairness/Justice: ethical choices are free from discrimination/favouritism

4. Common Good: assumes individual’s own good is linked to the good of society

5. Virtue: everyone holds internal morals that we maintain and hold onto

what are disadvantages of biotechnologies?

• Unequal access based on factors like race,sex, socioeconomic status

• Patenting of technology by private companies

• human/animal rights violation

• Violation of privacy

• Impacts on health

give the social and ethical benefits and disadvantages of Bt Cotton (pest resistant cotton)

Social	✅ increases crop yield removes pesticide use → lowers health risks, decreases environmental damage ❌ can lead to economic disparity - small farmers may struggle to afford new seeds
Ethical	❌ may unintentionally affect non-target insects lead to a resistant pest population farmer autonomy is reduced → big companies in charge

give the social and ethical benefits and disadvantages of Transgenic Salmon (GMO that grows faster)

Social ✅ Reduce overfishing Meet protein demands in growing populations ❌ Harm traditional fishing industries, small-scale farmers

Ethical ❌ Modifying growth rates may impact fish health/quality of life If GM salmon goes into the wild - inbreed with wild populations = reduction in natural biodiversity

what are some future directions for biotechnology?

1. Personalised Medicine: gene therapy could allow doctors to give treatments based off an individual’s genetic profile → more effective

2. Lab-Grown Meat: cultured meat from animal cells which reduces the need for livestock slaughter, sustainable, lower environmental impact, food security

3. De-extinction: using cloning and genetic technology to revive extinct species

4. Biodegradable plastic: engineering bacteria to make sustainable materials

what are potential benefits for using genetic technology?

• Disease prevention and treatment

• Agricultural productivity

• Environmental protection: reduce pesticide/fertiliser use, lower greenhouse emissions

• Sustainable food production: higher yield, faster rates

• Industrial and environmental applications: biofuels, biodegradable materials, bioremediation

what are positive changes to earth’s biodiversity due to genetic techniques?

• Increased genetic diversity in crops 

• Conservation efforts → cloning endangered species, preserve genetic material

• Bioremediation: restore ecosystems through GMOs

what are negative changes to earth’s biodiversity due to genetic techniques?

• Loss of natural biodiversity: GM crops outcompete wild relatives

• Monocultures: Heavy reliance on specific crops makes them vulnerable to disease

• Transgenes could spread to wild species

what are 4 methods of reproductive technologies?

1. artificial insemination

2. in vitro fertilisation

3. artificial pollination

4. selective breeding

what is the use of artificial insemination and its advantages?

use: livestock, infertility treatment in humans

advantages:

• Synchronise pregnancies

• Combat infertility issues

• Easier to transport frozen sperm

• Combats endangered species

what is the use of IVF and its advantages

use: occurs outside the body for infertility treatments in humans

advantages: freeze embryos, genetic screening

what is the use and advantages of artificial pollination?

use: Pollinating crops for desired offspring, Genetic experiments

advantages: controlled inheritance of traits

what is the use of selective breeding and it’s advantages?

use: Breeding offspring with desirable traits → agriculture, Friesian Bull: produces creamy milk

advantages: Desirable traits in offspring, is fertile, hybrid vigour

what are 3 types of cloning techniques

1. organism cloning

2. therapeutic cloning

3. gene cloning

what is the use and advantage of organism cloning?

Livestock industry

Definite inheritance of traits

what is the use and advantage of therapeutic cloning (SCNT)?

def. a technique used to create stem cells that are genetically matched to a patient

Medicine, stem cell technologies

Stem cells can differentiate

what is the use and advantage of gene cloning?

Medicine and industry

Large scale production of relevant proteins

what is the use and advantage of transgenesis?

Agriculture  eg. golden rice and frost berries

Organisms with multiple functions

what is the use and advantage of gene sequencing?

Medicine treatments and genetic research eg. BRCA1 gene

Identification of genetic disorders, risks, inheritance, forensic biology