Module 6: Genetic Change Flashcards
What are the main categories of mutagens?
Electromagnetic radiation
Chemicals
Naturally occuring mutagens
What is a point mutation?
When a single base pair of a genome is:
- Insertion, extra nucleotide added
- Deletion, nucleotide not included
- Substitution, wrong nucleotide added
What is a chromosome mutation?
A change to the arrangement or structure of a chromosome. Instead of changing a single base a very large section of DNA is being altered. They occur due to errors in cell divisions, more specifically in meiosis.
Types of chromosome mutations?
- Deletion - Section is broken off and lost
- Inversion - Section breaks off and reattaches in a different orientation.
- Translocation - Section breaks off to stick to another chromosome.
- Duplication - One section is copied more than once.
- Nondisjunction - When chromosomes dont separate problem.
Down syndrome?
The most common disease caused by chromosomal mutation. It is also referred to as trisomy 21, where people have 3 copies of chromosome 21. Occurs due to non disjunction which results in a gamete receiving 2 of chromosome 21, resulting in the zygote have 3.
Types of Genetic change? What are they caused by?
Mutations: These are accidental, in which a disruptive process alters the base sequence of DNA. They can be caused by environmental agents called mutagens, or by a cellular error, when a mistake is made during cell division.
Biotechnology: Where we deliberately alter DNA.
Types of cellular error?
Chromosomal
Point
How does electromagnetic radiation work? (2 examples)
As short wavelength, high energy waves move through matter, they give energy to atoms they hit, causing them to vigorously vibrate and lose electrons in the process. This causes damages as chemical bonds. Examples of EM radiation are UV rays from the sun, and gamma rays from uranium-236.
How do chemical mutagens work? (3 examples)
There are many different ways chemicals cause mutations:
- Chemical is incorporated into DNA, instead of proper nucelotides. E.g. 5-bromodeoxyuridine is mistakenly taken to be Thymine by DNA polymerase.
- Chemical inserts itself into DNA. E.g. Actinomycin D creates a bulge in DNA, and prevents replication.
- Chemical makes gaps in DNA, like dimethyl sulfate, which breaks the bond between the base and a sugar of a nucleotide.
How do naturally occuring work?
They specifically come from fungi, plants and animals. Mycotoxins are poisonous chemicals produced by fungi. Cycasin is a mutagenic chemical produced in the leaves of cycad plants. Dimethylnitrosamine is produced in the stomach when nitrite is consumed by an animal, which is found in ham and sausage.
Why is mutation the ultimate source of genetic variation?
Because it is the only process that can introduce new alleles into the population.
What happens if a gene is not fully intact?
Genes produce proteins when they are fully intact. If a gene has been ‘broken’ to allow for the insertion of another gene, or due to mutation, it will not be functional.
Effects of UV radiation?
UV radiation is a known carcinogen, meaning that it can cause genetic mutations that lead to cancer. For example, mutations might damage tumour suppressor genes, leading to cell proliferation. A type of skin cancer known as melanoma can occur die to chronic carcinogen (UV radiation) exposure.
What is cancer?
Cancer is the term given to a group of diseases that involve abnormal cell growth, typically as a result of genetic mutations.
Why is mutation bad?
As DNA is used as a template for mRNA during protein synthesis, if even a single nucleotide is altered, the order of bases on DNA will be changed, resulting in the wrong amino acids being used to build the chain, and creating a different or dysfunctional protein.
Effects of point mutation?
Insertion and Deletion will affect the nucleotide sequence, and thus every subsequent codon after the site of mutation. These are called frameshift point mutations.
During substitution, it can either be mis-sense, non-sense or silent.
- Missense mutation is when a substitution results in the codon coding for a different amino acid.
- Nonsense is when substitution results in he formation of a stop codon.
- In a silent mutation, the wrong nucleotide is substituted in, but there is no change that occurs.
Example of point mutation disease?
Sickle Cell anaemia is a genetic disorder where people have misshapen RBC. Caused by a single substitution in the gene that creates haemoglobin, going from GAG to GTG. This causes the RBC to fold into an abnormal shape, where they can’t carry oxygen as efficiently and cause blood clots.
What are the effects of chromosomal mutations?
In all chromosomal mutations, if breakage occurs in the middle of a gene, the gene is destroyed and becomes inactive. In deletion, inversion and translocation, the genes are moved to a new place. In duplication, we can end up with changes in the amount of proteins produced.
What is a germ-line mutation?
A change of DNA in a germ cell, which are the cells that divide during meiosis to form sex cells. These mutations are passed from parents to offspring. They do not affect the parent. Examples of germ-line mutation is Down Syndrome, or trisomy 21, where when a germ cell undergoes meiosis, 2 chromosome 21s go into a sex cell, instead of one (non-disjunction)
Somatic mutations?
Somatic cells form the body tissue of an organism. A somatic mutation can only affect the individual, and cannot be passed onto offspring. For example, lung cancer is a disease caused by uncontrolled cell growth in the lungs as a result of mutagens like cigarette smoke.
Example of a mutation to coding DNA?
Change to DNA which codes for the amino acid sequence of a protein. For example, sickle cell anaemia is a genetic disorder where people have misshapen red blood cells, caused by a substitution point mutation in DNA which codes of haemoglobin, from GAG to GTG. Changes amino acid from glutamic acid to valine.
What are the effects of mutation to non-coding DNA? (1 example)
Change in DNA that doesn’t code for proteins. Instead, they can act as:
- Templates in the creation of functional RNA
Mutation will cause issues with protein synthesis
- Regulatory sequences, that control the amount of proteins produced by coding DNA
Mutation may cause gene transcription levels to change, that is the amount of proteins produced may increase or decrease.
- Repetitive sequences, regions of DNA which have the same sequence repeated many times, which have mostly been introduced to us by viruses.
Mutation will have no effect.
Example is lung cancer, which is a mutation in the regulatory sequences, which control cell division and growth.
What is a gene pool?
All the alleles for all genes in a population. Gene pools are dynamic, affected by gene flow, drift, mutations and selection pressures. Larger gene pool is good for genetic diversity
Factors affecting gene pool?
Gene flow: Movement of alleles between populations due to movement of organisms. If gene flow between populations is high, their gene pools will be similar, and vice versa
Genetic drift: Random events occuring can lead to changes in gene pool, such as natural disasters. The “lucky” individuals survive, not the “better” ones.
Mutations: Source of new alleles.
Selection pressures: Any external factor that affects an organism’s ability to survive in it environment. The individuals that are better suited in different selection pressures will go on to give their traits to their offspring.
What is the founder effect?
When a small group of individuals are separated from their original, larger population, and move to a new location to establish a new population
What is bottleneck effect?
When a species experiences an event that suddenly and significantly reduces its population and gene pool
Inbreeding?
Occurs when populations become smaller and isolated. Results in an accumulation of mutations, as many mutations are recessive, and inbreeding increases the likelihood that offspring receive two copies of the mutation.
Historical examples of biotechnolgy?
- Selective breeding
- Fermentation
- Traditional medicine
Female and Male part of flowers?
Pollen is produced in the stamen
The stigma receives the pollen
How do we clone whole plants?
- Cutting and grafting
Cutting:
Section of plant is removed, and placed in soil or water where it develops its own roots, stems and leavings until it grows to full size.
Grafting:
Cutting from of a plant is bound to the cut stem of another plant with already developed roots, where they fuse and then grow. - Tissue cultures
Section of parent plant is pulverised to release individual plant cells. Cells are grown on a medium containing nutrients and hormones that promote growth, which eventually grow into full sized plants.
How do we clone animals?
- Artificial Embryo twinning
Egg is fertilised, zygote is allowed to develop, forming a clump of unspecialised cells, where each cell is capable of developing into a complete organism. These are then separated and each transplanted into different surrogate mothers, who will give birth to multiple, genetically identical offspring. - Somatic Cell Nuclear transfer
Donor cell is taken from the organism that will be cloned, and an unfertilised egg is taken from a female donor. DNA in the egg is removed, and replaced with the DNA from the donor cell. Egg cell is triggered to divide by an electrical impulse, developing into an embryo. This is then transplanted into a surrogate mother, who will give birth to a clone.
Why do we clone? (3 reasons)
- Scientific Research
Animal testing, as cloned animals will have the same reactions to drugs, providing reliable responses to drugs used in research. E.g oncomouse - Argriculture
As desirable traits are able to be passed onto offspring, which can often be faster and more reliable than conventional breeding. For example, tissue cultures enable the production of thousands of genetically identical plants in a short time. - Wildlife Conservation
Crucial in prevention extinction of critically endangered species. E.g. northern white rhinoceros, which only have 2 females remaining
What is recombinant DNA? How is it cloned?
DNA which contains genes from two or more different sources. DNA is cloned ‘in vivo’, where a gene is inserted into a bacterium, which makes copies of the gene for us. One example is cloning the human insulin gene in E.coli
What is PCR?
Polymerase Chain reaction, where a specific region of DNA is cloned ‘in vitro’.
Applications of Gene cloning (4)
DNA Sequencing - Gene cloning makes enough gene copies for scientists to perform analysis on base sequence.
DNA Profiling - Scientists can create a DNA profile by amplifying (cloning) certain genes.
Genetically modified organisms - Genes can be added or removed from organisms to allow understanding of how a gene works
Gene Therapy - Scientists replaced a disease-causing gene with a normal gene.
Disadvantages of organism and gene cloning?
- Extremely expensive
- Ethical concerns, as cloned animals tend to suffer more adverse health issues and higher mortality rates.
- Reduces genetic diversity, leaving population more vulnerable to sudden environmental changes.
How is recombinant DNA made?
- Isolation - DNA fragments are extracted from their natural sources, the target gene, which codes for the protein of interest, and scaffold DNA, which the target gene will be inserted into, usually plasmids from bacteria.
- Digestion - Using the same restriction enzyme on both DNA, which cuts the DNA at a specific base sequence. The enzymes create ‘sticky ends’ at the ends where there are exposed bases.
- Insertion - The target gene and open plasmid are mixed together, where they will spontaneously fuse to form a recombinant plasmid at their ‘sticky ends’.
- Ligation - DNA ligase fixes the broken sugar-phosphate backbone of the recombinant DNA.
How is DNA amplification done using bacterial transformation?
Bacteria duplicates very quickly, so bacterial transformation is a very effective method of amplifying DNA. We must first introduce the recombinant plasmid to the bacterial cell. First, the plasmids and bacteria are both added to a solution containing calcium ions, which disrupt the cell membrane of bacteria, and allowing recombinant DNA to move into the cell. Next, the bacteria is heat shocked, quickly increasing the temperature in a short time which forces the recombinant DNA into the bacteria cells. Finally, the bacteria is transferred to a nutrient rich broth, at their optimal temperature/ (37 degrees).
How many bacteria become transformants during transformation?
Only 1/10000 become transformants and take up the plasmid DNA, as either the bacteria doesn’t take up the plasmid by chance, or the heat shocking kills the bacteria.
How are transformant bacteria identified?
Scientists use plasmids with a selectable marker, a gene that produces easily observable characteristics, usually an antibiotic resistance gene.
What happens to transformants?
Either they are used to make the protein of interest, which is extracted and purified to be used.
Or, they could be used to make the recombinant plasmid, extracted from the transformants, which could be used in DNA sequencing, profiling or making transgenic organisms.
Advantages of use DNA recombinant technology over artificial selection?
- Allows for the ability to choose from the genes of unrelated organisms for the gene of interest, significantly improving the chance of finding a target gene.
- It is faster, as it can be incorporated immediately into the species, while artifical selection can take multiple generations.
- It is more controlled, as artificial selection can give rise to different unrelated traits.
What is the difference between a transgenic organism and a GMO?
GMO is an umbrella term for any organims that has had their genome modified, while a transgenic organism is one that has had DNA added to their genome, so possesses DNA from two or more different sources.
Techniques for making transgenic organisms (4 examples)
- Bacterial plasmids
- Microinjection - DNA from one species is inserted into the cell of another using a micropipette
- Biolistics - a gene gun shoots small metal bullets coat in DNA into the nucleus of a cell, mostly used for plant cells
- Electroporation - cells are exposed to a series of short electrical impulses, which create holes in the cell membrane through which DNA can move into the cell
Uses of transgenic organisms? (4 examples)
- Increasing crop and livestock livestock
BT cotton contains a gene from a soil bacteria which codes for a toxin that kills cotton-eating caterpillars. - Increasing crop productivity
Golden rice contains 2 additional genes from daffodils and a soil bacterium, which allows the plant to produce rice rich in beta-caratene, which is the precursor to vitamin A. - Produce therapeutic products
Insulin is created by inserting the human gene that codes for it in E.coli, which will cause the bacteria to produce insulin which can be harvested and purified. - Help study human diseases, by predicting how certain drugs and treatments will affect humans.
The OncoMouse contains a human cancer gene, increasing the likelihood for developing cancer, and helping assist the development of cures for human cancer.
Ethical concerns with transgenic species? (1 pro 1 con)
Advantage:
Provided the ability to produce proteins without the need to extract from animals. Example, human insulin can be produced using bacterial plasmids, instead of extracting it from pigs.
Disadvantage:
There are ethical concers involving transgenic species that are used for testing. For example, the Oncomouse is genetically modified to develop cancer in the first few weeks of its life, limiting its life span to only eight weeks.
Effect of biotechnology on biodiversity? (2 pros 2 cons)
Pros:
- Artificial insemination and artifical pollination can be used to cross organism from the same species that would otherwise be unable to breed due to geographical barriers.
- Recombinant DNA can move genes between organisms, creating transgenic and biodiverse organisms.
Cons:
- Intensive farming promotes the growth of crops and animals with “desirable” traits and lead to low biodiversity, leaving them susceptible to sudden envionmental changes.
- If GMOs escape into the wild, they may outcompete non-GMOs, decreasing biodiversity in the whild.
Ethical concerns of biotechnology? (3 examples)
Examples:
- Genetic screening during pregnancy
Can be used to determine if an unborn baby has genetic abnormalities, which may lead to suffering of the child or parents, allowing parents to make an informed decision as to whether or not they would like to continue with the pregnancy.
- GMOs
Transferring genes between organisms can contradict with people’s beliefs.
- Animal welfare
It has positive and negative. For example, insulin can now be extracted from vats of transgenic bacteria, instead of being extracted from pigs. Negatives include GMOs that suffer from poor health. OncoMouse.
