DNA probes

what is a DNA probe? what are DNA probes used for?

• piece of ssDNA complementary to sequence of interest, chemical attached to a radioactive/fluorescent dye

• used to locate specific alleles of genes and to screen patients for heritable conditions, drug responses or health risks

why are DNA probes labelled? what are they usually labelled with?

• for identification/detection

• radioactive/fluorescent dye

how are DNA probes produced?

• target allele’s base sequence identified using DNA sequencing

• complementary probe made using gene machine

• sequence replicated using PCR

describe the process of screening DNA for a specific allele using a DNA probe:

• individual’s DNA strands heated, causing them to separate into 2 ssDNA

• DNA sample digested into fragments using restriction enzymes

• add fluorescently/radioactively labelled DNA probes

• hybridisation occurs - DNA probes bind w/ target sequence

• DNA washed so any XS unbound DNA probes washed away

• visualise any DNA probe which has been hydrolysed to DNA fragments using UV light/radiography (respectively)

• the presence of the radioactive/fluorescent label indicates that the allele of interest is present in the DNA sample

describe the DNA hybridisation stage:

• DNA sample heated, causing it to denature so H bonds between bases break and becomes ssDNA

• the ssDNA sample is mixed w/ the DNA probe and cooled so any complementary sequences can align and anneal, forming H bonds

• some of the patient’s DNA samples will anneal back together, but some will anneal w/ DNA probe

give one advantage of having your DNA screened:

• acts as personalised medicine - e.g. certain drugs may be more/less effective based on genotype

• so allows best dose to be determined - increases effectiveness/safety and helps save money

what is genetic counselling?

• form of social work in which people have their family history researched to consider the likelihood of them carrying any alleles linked to diseases/disorders

• e.g. if you find you are likely to carry an allele relating to a certain cancer, you can opt for more regular tumour screenings