Lecture 31 Flashcards
What is forward genetics?
When studies move from the phenotypes to the DNA
What is reverse genetics?
When studies move from the DNA to the phenotype
What is polymorphism with regards to genetics?
Genetically determined variation, it is this which forms the basis of genetic studies
What are allele frequencies?
A measurement which can be used to assess the amount of polymorphism in a population
What are phenotypic markers and why might they be limited?
They are the observation of simple traits for example mendels smooth and wrinkled peas, theses are limited in genetic studies as they must be simple traits if they are to be used as markers and it is fair more likely the trait is complicated through multigenicity and environmental factors?
How can the limitations of phenotypic markers be overcome?
Rather than using phenotypic markers, protein and DNA markers can be used as they directly measure the genetic variation in a population
What are the features of DNA markers?
There is a larger number available than protein markers and all genetic variation can be assessed including changes in noncoding regions, like regulatory elements or silent mutations
There i not need to get a specific type of cell as all cells have all the genomic content even if it is not expressed in all cells
Most are selectively neutral which makes them better than protein markers for population studies which may be placed under selection pressures
What are the applications of DNA based markers?
Random markers can be used for DNA fingerprinting can be used identify individuals in forensics and paternity tests as well as construction of fine resolution genetic maps, population and diversity studies
Markers linked to specific loci can be used to identify single genes which may affect important traits as well as in mulitgenic analysis
What are restriction length polymorphisms?
A base change in the DNA which causes the loss or gain of a recognition site for a restriction enzyme change the number and length of the strands that this is chopped up into which can be noted by gel electrophoresis
What causes restriction length polymorphisms?
Base changes which remove and add sites ass well as additions and deletions in between the sites
How are restriction length polymorphisms visualised?
Southern hybridisation which uses radioactivity and large amounts of DNA
DNA is cut with a specific enzyme and undergoes gel electrophoresis where it is sucked up by filter paper and hybridized with unique radioactive probes to allow visualisation
Visualisation can also be achieved by using PCR to amplify the probe region using specific primers
How many cuts would be expected if the human genome was cut with EcoRI?
EcoRI cuts roughly once every 4 kb so it the human genome was cut there would be roughly 750,000 fragments expected
What are important considerations when using RFLPs to predict disease?
Recombination can lead to false predictions, the amount of false prediction rate is proportional to linkage 1cM=1% error
This can be combated by using closer genetic markers and flanking markers
What are the features of single locus marker?
RFLPs, Microsatellites and SNPs
In these there are only one locus at a time with a defined location on a chromosome they are the most widely used but more expensive to develop as clones or sequence is needed
results can be compared between individuals and species
What are the features of multi-locus markers?
Minisatellites, RAPDs and AFLPs are all multi-locus markers there are many loci at once but they have unknown locations on a chromosomes, there is zero development cost as there are universal primers or probes
results are comparable within a species but not between divergent species
They are useful for uncharacterised species eg ecological studies
