Differences in DNA between individuals of the same species can be exploited for identification & diagnosis of heritable conditions Flashcards
What are DNA probes?
● Short, single stranded pieces of DNA
● With a base sequence complementary to bases on part of a target allele / region
● Usually labelled with a fluorescent or radioactive tag for identification
Suggest why DNA probes are longer than just a few bases
● A sequence of a few bases would occur at many places throughout the genome
● Longer sequences are only likely to occur in target allele
What is DNA hybridisation?
● Binding of a single stranded DNA probe
to a complementary single strand of DNA
● Forming hydrogen bonds / base pairs
Explain how genetic screening can be used to locate specific alleles of genes
- Extract DNA and amplify by PCR
- Cut DNA at specific base sequences (either side of target gene) using restriction enzymes
- Separate DNA fragments / alleles (according to length) using gel electrophoresis
- Transfer to a nylon membrane and treat to form single strands with exposed bases
- Add labelled DNA probes which hybridise / bind with target alleles (& wash to remove unbound probe)
- To show bound probe, expose membrane to UV light if a fluorescently labelled probe was used
OR use autoradiography (expose to X-ray film) if a radioactive probe was used
What is gel electrophoresis
● A method used to separate nucleic acid (DNA / RNA) fragments OR proteins
● According to length / mass (number of bases / amino acids) AND charge (DNA is negatively charged due
to phosphate groups and protein charge varies based on amino acid R groups)
Explain how gel electrophoresis can be used to separate DNA fragments
- DNA samples loaded into wells in a porous gel and
covered in buffer solution (which conducts electricity) - Electrical current passed through → DNA is negatively
charged so moves towards positive electrode - Shorter DNA fragments travel faster so travel further
How can data showing results of gel electrophoresis be interpreted?
● Run a standard with DNA fragments / proteins of known lengths under the same conditions
● Compare to position of unknown DNA fragments / proteins to estimate their size
● Shorter DNA fragments/ proteins travel further / faster
Describe examples of the use of labelled DNA probes
● Screening patients for heritable conditions (eg. cystic fibrosis)
● Screening patients for drug responses (some alleles code for enzymes involved in drug
metabolism that enable better responses to certain drugs)
● Screening patients for health risks (some alleles predispose patients eg. to high blood cholesterol)
Describe the role of a genetic counsellor
- Explain results of genetic screening, including consequences of a disease
- Discuss treatments available for genetic condition
- Discuss lifestyle choices / precautions that might reduce risk of a genetic
condition developing eg. regular screening for tumours or a mastectomy - Explain probability of condition / alleles being passed onto offspring →
enable patients to make informed decisions about having children
What is personalised medicine?
● Medicine tailored to an individual’s
genotype / DNA
● Increasing effectiveness of treatment
eg. by identifying the particular
mutation / allele causing cancer and
treating it with tailored drugs
Evaluate the screening of individuals for genetically determined conditions
and drug responses
✓ Can enable people to make lifestyle choices to reduce chances of diseases developing
✓ Allows people to make informed decisions about having their own biological children
✓ Allows use of personalised medicines, increasing effectiveness of treatment
𝖷 Screening for incurable diseases or diseases that develop later in life (where nothing
positive can be done in response) may lead to depression
𝖷 Could lead to discrimination by insurance companies / employers
𝖷 May cause undue stress if patient does not develop the disease
