Locating Genes, Genetic Screening, And Counselling Flashcards
Many humans diseases have a genetic origin. What are these the result of
A gene mutation
How do we know exactly where a particular DNA sequence (gene) is located
Labelled DNA probes and DNA hybridisation
What is a DNA probe
A short, single stranded length of DNA that has some sort of label attached that makes it identifiable.
What are the two most commonly used probes
Radioactively labelled probes - which are made up of nucleotides with the isotope 32P. 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 sequence
Describe how DNA probes are used to identify particular alleles of genes
A DNA probe is made that has base sequences that are complementary to part of the base sequence of the DNA that makes up the allele of the gene that we want to find
The double stranded dna that is being tested is treated to separate its two separate strands
The separated DNA strands are mixed with the probe, which binds to the complementary base sequence on one of the strands. This is known as DNA hybridisation
The site at which the probe binds can be identified by the radioactivity or fluorescence that the probe emits
When does DNA hybridisation take place
When a section of DNA or rna is combined with a single stranded section of DNA which has complementary bases
Before DNA hybridisation can take place, the two strands of DNA molecule must be separated, how is this achieved
By heating DNA until its double strand separates into it’s two complementary single strands (denaturation). When cooled, the complementary bases on each strand recombine (anneal) with each other to reform the original double strand
Given time all strands in a mixture of DNA will pair up with their partners. If, However, other complementary sections of DNA are present in the mixture as the DNA cools, these are just as likely to anneal with one of the separated strands as the two strands are with one another
Describe the process to locate a specific allele of a gene
- The sequence of nucleotides on the mutated gene is determined by DNA sequencing. Genetic libraries now store the DNA sequences of many of the genes responsible for common genetic diseases
- Fragment of DNA with complementary bases to the mutant allele of the gene is produced
- DNA probe is formed by fluorescently labelling the DNA fragment
- Pcr techniques are used to produce multiple copies of the dna probe
- Probe is added to single stranded DNA fragments from the person being screened
- If the donor has the mutated gene, some donor DNA fragments will have a base sequence that is complementary to the probe and the probe will bind to its complementary bases on the donor DNA
- These DNA fragments will now be labelled with the probe and can be distinguished from the rest of the fragments
- If complementary fragments are present, the DNA probe will be taken up and the dye will fluoresce - this is detected by a special microscope. If complementary fragments are not present, the DNA probe will not fluoresce
When may gene mutations arise
If one or more nucleotide bases in DNA are changed in any one of a variety of ways
What can screening do
Determine the probability of couple having offspring with a genetic disorder
Why is genetic screening good for cancer
As it can detect oncogenes, which are responsible for cancer.
So therefore if a mutated gene is detected by genetic screening, individuals who are at a greater risk of cancer can make informed decisions about their lifestyle and future treatment
How is genetic screening good for personalised medicines
Allows doctors to provide advice and health care based on an individuals phenotype
Can see which drug is most effective according to the genotype and the dosage - this saves money on overprescribing drugs
What is genetic counselling
Special form of social work, where advice and info are given that enable people to make personal decisions about themselves or their offspring
