Locating genes, genetic screening and counselling Flashcards
What is a DNA probe ?
a short, single-stranded length of DNA that has some sort of label attached that makes it easily identifiable
What are the two most commonly used probes ?
radioactively labelled probes- the probe is identified using an X-ray film that is exposed by radioactivity
Fluorescently labelled probes- which emit light under certain conditions, for instance when the probe has bound to the target DNA sequence
Explain how a DNA probe can be used to identify particular alleles of genes
a DNA probe is made with a sequence of bases that are complimentary to the part of the base sequence of the DNA that makes up the allele that we want to find.
The double stranded DNA that is being tested is treated to separate the two strands.
The separated DNA strands are mixed with the probe which binds to the complimentary base sequence on one of the strands. (DNA hybridisation)
The site at which the probe binds can be identified by the radioactivity or fluorescence that the probe emits.
What is DNA hybridisation
DNA hybridisation takes place when a section of DNA or RNA is combined with a single stranded section of DNA which has complimentary bases.
What must happen before DNA hybridisation can take place ?
the two strands of the DNA molecule must be separated. This is achieved by heating DNA until its double strands separates into its two complimentary single strands.
When cooled the complimentary bases on each strand recombine with eachother to reform the original double strand.
Outline the process of genetic screening for a disease
determine the order of nucleotides on the mutated gene by DNA sequencing
produce a fragment of DNA that has complimentary bases to the mutated portion of the gene
label the fragments to produce a DNA probe
make multiple copies of the donor DNA using PCR techniques
add the probe to the DNA fragments from the individual being tested. If the donor has the mutated allele the probe will bind to the complimentary bases on the donor DNA
These fragments will now be labelled and can be distinguished from the rest of the DNA.
What does Genetic screening do ?
Screening can determine the probabilities of an individual or a couple having offspring with a genetic disorder.
What is the benefit of genetic screening of tumour suppressor genes ?
if the mutated tumour suppressor gene is detected by genetic screening, the individuals who are at a greater risk of cancer can then make informed decisions about their life style and future treatment.
They can choose to eat more healthily and avoid mutagens.
What is an advantage of genetic screening ?
personalised medicine
What is personalised medicine ?
Some peoples genes can mean that a particular drug may be either more or less effective in treating a condition. By genetically screening patients, doctors and pharmacists can determine more exactly, the dose of a drug which will produce the desired outcome. This can save money and in some cases it avoids medications that could cause harm and raising false hopes.
What is genetic counsellor ?
genetic counselling is like a special form of social work where advice and information are given that enable people to make personal decisions about themselves or their offspring.
What is the aim of genetic counselling ?
One important aspect of genetic counselling is to research the family history of an inherited disease and to advise parents on the likelihood of it and their children.
What can a counsellor inform people of ?
emotional
psychological
medical
social
economic consequences
on the basis of the advice the couple can then choose whether or not to have children.
Where is Genetic fingerprinting used?
forensics, plant and animal breeding and medical diagnosis,to determine family relationships, to determine genetic diversity in a population
How does genetic fingerprinting work ?
relies on the fact that the genome of most eukaryotic organisms contains many repetitive, non coding bases of DNA. These are known as Variable number tandem repeats (VNTRs)
For every individual the number and length of VNTRS has a unique pattern.
The more closely related two individuals are, the more similar the VNTRS.
What is Gel electrophoresis ?
Gel electrophoresis is used to separate DNA fragments according to their size
What does VNTRS stand for ?
variable number tandem repeats
Explain the making of a genetic fingerprint
DNA is extracted from the sample
restriction endonucleases cut the DNA into fragments
fragments are separated using gel electrophoresis. DNA fragments treated to produce single stranded DNA fragments
DNA fragments are transferred from the gel to nylon membrane
DNA probes are added to label the fragments. These radioactive probes attach to specific fragments
Membrane with radioactively labelled DNA fragments is placed onto an X-ray film.
Development of the X-ray film reveals dark bands where the radioactive DNA probes have attached.
Explain the process of Gel electrophoresis
The DNA fragments are separated according to size. The DNA fragments are placed on to an agar gel and a voltage is applied across it. The resistance of the gel means that the larger the fragments, the more slowly they move. Therefore over a fixed period, the smaller the fragments move further than the larger ones. If the DNA fragments are labelled for example with radioactive DNA probes their final positions in the agar gel can be determined by placing a sheet of X-ray film over the agar gel for many hours.
Explain how genetic fingerprinting can be used to help resolve questions of paternity
individuals inherit half their genetic material from their mother and half from their father. Therefore each band on a DNA fingerprint of an individual should have a corresponding band in one of the parents DNA finger prints.
Explain how genetic fingerprinting can be used to determine genetic variability within a population
the more closely related two individuals are related the closer the resemblance of their genetic fingerprints,
What is the genetic diversity like of a population that has very similar genetic fingerprints ?
low genetic diversity
Explain how genetic fingerprints can be used in forensic science
DNA is often left at the scene of a crime, for example blood at the scene of a violent crime
Genetic fingerprinting can establish whether a person is likely to have been present at the crime scene.
Even if there is a close match between a suspects DNA and the DNA found at the crime scene, it does not follow that the suspect carried out the crime. For example,
The DNA may of been left on some other innocent occasion
The DNA may belong to a close relative
Explain how Genetic fingerprints can be used in medical diagnosis such as diagnosing Huntington’s disease
Genetic fingerprints can help in diagnosing diseases such as Huntington’s.
A sample of DNA from a person with the allele for Huntington’s disease can be cut with restriction endonucleases and a DNA fingerprint prepared. This can then be matched with fingerprints of people with various forms of the disease and those without the disease. In this way the probability of developing symptoms and when can be determined.
Explain how Genetic fingerprinting s used in plant and animal breeding
Genetic fingerprinting can be used to prevent undesirable inbreeding during breeding programmes on farms or in zoos.
It can also identify plants or animals that have a particular allele for a desirable gene.
Individuals with this allele can be selected for breeding in order to increase the probability of their offspring having the characteristic it produces.
Another application is the determination of paternity in animals and thus establishing the family tree of an individual.
Explain why a patient may choose to receive genetic counselling
to help decided whether or not to undergo genetic screening
to discuss treatments available for a genetic condition
deciding whether or not to have a child
to help a patient learn about a particular condition
to discuss lifestyle choices that might reduce the risk of a genetic condition developing.
