Differences in DNA between individuals of the same species can be exploited for identification & diagnosis of heritable condition 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
xplain how genetic screening can be used to locate specific alleles of gene
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
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
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
For ✓ Some people could be heterozygous / carriers (eg. in families with a history of a disease)
✓ Can enable these people to make lifestyle choices to reduce chances of diseases
developing, to prevent suffering / death
✓ Allows people to make informed decisions about having their own biological children
✓ Allows use of personalised medicines, increasing effectiveness of treatment
Against 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 May cause undue stress if patient does not develop the disease
𝖷 Could lead to discrimination by insurance companies / employers
𝖷 Many diseases are rare
𝖷 Many are caused by many genes so would need too many probes (expensive
