Genetics Flashcards
What 3 laws did Mendel derive from his work on cross breeding pea plants?
- Law of dominance – some alleles are dominant and some are recessive. An organisms with at least one dominant allele with display the effect of the dominant alle.
- Law of segregation – during gamete formation, the alleles for each gene are segregated, so each gamete carries only one allele for each gene.
- Law of independent assortment – genes are often on separate chromosome, so can segregate independently during the formation of games and can therefore often be inherited independently of each other.
What is the difference between single-gene traits and multifactorial genes?
Single gene traits can be a dominant or recessive allele of a positive or a negative gene.
Multifactorial genes can be the interaction of multiple genes or by a combination of genetic and environmental effects.
Describe 6 situations of non-Mendelian inheritance.
- Incomplete dominance: neither one of the alleles are dominant so the alleles combine and create an intermediate (hair length in rabbits).
- Co-dominance: both alleles are expressed not resulting in a merge but both traits are visible (roan coat).
- Genetic Linkage: when genes are closely located on the same chromosome and the genes will be inherited in a linked fashion.
- Multiple alleles: in nature genes often exist in several different forms and have more than 2 alleles.
- Sex-linked inheritance: genes located on sex chromosomes are dependent on gender (colour blindness).
- Mosaicism: Individuals that possess cells with genetic differences from the other cells in their body (tortoiseshell cats).
Define penetrance.
The proportion of individuals with a particular allele that exhibit the associated phenotype, useful for measuring disorders where a single gene plays a major but not exclusive role.
Describe the process of cloning.
- Cells are taken from the animal that is going to be cloned. These can be differentiated cells from any part of the body, as these cells were never going to pass on their DNA to the next generation.
- Differentiated cell is inserted into the cytoplasm of an unfertilised egg from a donor mother from which the DNA has been removed. The insertion of the DNA into the unfertilised egg is nowadays generally done by an electric pulse. If the cells are held very close together so that their membranes are close, then an electric pulse causes the membranes to fuse and the nucleus comes into the cytoplasm of the egg cell.
- This produces this reconstructed zygote, which then divides a few times in vitro and then it is implanted into a foster mother who give birth to the offspring if everything works.
Why is cloning used?
The offspring will not be an exact genetic copy of the initial animal if it has the mitochondrial DNA from it.
Cloning allows you to control the mitochondrial DNA inherited. Not to clone cows or sheep to make our farm fields look uniform, but so that if an animal is created that produces high valuable medicine, this animal can be cloned to maintain that high value phenotype rather than let sexual reproduction muddle it all up again by introducing variation and therefore risking losing that special phenotype.
What is a PCR?
Polymerase Chain Reaction, a method to amplify a region of DNA that you target. Every cycle produces double the amount of DNA.
What is needed to conduct a PCR?
- Template DNA
- DNA polymerase. Needs to be thermostable because you don’t want the enzyme to denature when you heat the sample in the denaturing step of the PCR cycle. So a DNA polymerase Taq is often used, this is isolated from an organism living in deep sea hot vents, which is optimised to survive hot temperatures.
- Nucleotides
- 2 specific oligonucleotide primers, which are short bits of ssDNA, about 15-25 nucleotides long
- 2 primers, one at each end of the bit of DNA that you wish to amplify. They anneal with the template DNA, so the material that you want to amplify
How is a PCR carried out?
- Heat the double strand, which is used as a template, in order to denature it and make it single stranded.
- Cool to allow primers to bind. One primer binds to one end of the target DNA and the other primer binds to the other end.
- This is warmed a little so that DNA polymerase can extend the DNA from the primers from the 3’ using the nucleotides.
What is an advantage and disadvantage of a PCR?
+ Very little template DNA is needed as it is a very sensitive method, as little as one molecule would be enough. Which allows the use of very non-invasive sample collection, like a mouth swap for example.
- However, this sensitivity is also a disadvantage as it is also very sensitive to contamination. So it important to keep that in mind when you get results back that are odd. Contaminating a PCR reactions is easy, DNA can blow into the window, come from stroking a cat, a sneeze or most commonly from the technician setting up the PCR, and it can give misleading results.
What is gel electrophoresis?
A way to separate DNA molecules on the basis of size and detect PCR products.
Describe the process of gel electrophoresis.
- The DNA backbone is negatively charged so it will move towards the positive electrode if it is put in an electric field.
- The agarose gel has little wells, in which you can add your DNA samples.
- Cover it with a conducting buffer and then apply an electric field in a gel tank.
- The DNA then moves towards the positive electrode, but it will have to move through this gel.
- Small molecules move faster through the gel then large molecules and will therefore migrate further down the gel.
- The DNA can be visualised by using a fluorescent dye.
- Comparing your samples with a DNA ladder, which is a mixture of DNA molecules of different known sizes, allows you to see very easily what the sizes are of the DNA in the sample that you have run.
What 2 things does gel electrophoresis allow you to detect?
Is a PCR band present?
What is the size of the DNA?
What are the applications of DNA sequencing?
- DNA polymerase needs a primer to start synthesising DNA, so one primer is required to determine where you will start reading the DNA, and then DNA polymerase can add nucleotides.
- There are different methods to detect those nucleotides that get added by polymerase.
- The latest techniques do not work by making many copies of DNA. They can sequence a single molecules of DNA and read millions of base pairs in one go. Often contain lots of nanopores, that generate an electrical as molecules pass over the pores.
What are the 2 reasons to make genetically modified organisms?
- To use these genetically modified organisms as factories to make a protein drug. The purpose is to use an organism to do in vivo chemistry for us that is too difficult or expensive to do in a lab, and you purify the drug. This is example of a protein that is used as a vaccine, insulin is another one.
- The second reason is to change an organism is to create an organisms with altered properties. For example a salmon with altered level of growth hormone levels to farm bigger salmon, or disease resistant animals, or pesticide resistant plants.
