8.4.2 Differences in DNA between individuals of the same species can be exploited for identification and diagnosis of heritable conditions ( 8.0 control of gene expression)

Question 1

what are DNA probes

Answer 1

• 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

Question 2

suggest why DNA probes are longer than just a few bases

Answer 2

• a sequence of a few bases would occur at many places throughout the genome
• longer sequences are only likely to occur in a target allele

Question 3

what is DNA hybridisation

Answer 3

• binding of a single stranded DNA probe to a complementary single strand of DNA
• forming hydrogen bonds

Question 4

explain how genetic screening can be used to locate specific alleles of genes

Answer 4

1) extract DNA and amplify by PCR
2) Cut DNA at specific base sequences using restriction enzymes
3) Separate DNA fragments / alleles using gel electrophoresis
4) Transfer to a nylon membrane and treat to form single strands with exposed bases
5) Add labelled DNA probes which hybridise / bind with target alleles
6) To show bound probe , expose membrane to UV light if a fluorescently labelled probe was used or use autoradiography if a radioactive probe was used

Question 5

what is gel electrophoresis

Answer 5

• a method used to separate nucleic acid ( dna / rna) fragments or proteins
• according to length / mass and charge ( DNA is negatively charged due to phosphate group and protein charges varies based on amino acid R groups )

Question 6

explain how gel electrophoresis can be used to separate DNA fragments

Answer 6

1) DNA samples loaded into wells in a porous gel and covered in buffer solution
2) Electrical current passed through => DNA is negatively charged so moves towards positive electrode
3) Shorter DNA fragments travel faster so travel further

Question 7

How can data showing results of gel electrophoresis be interpreted

Answer 7

• 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

Question 8

Describe examples of the use of labelled DNA probes

Answer 8

• screening patients for heritable conditions
• screening patients for drug responses
• screening patients for health risks

Question 9

Describe the role of a genetic counsellor

Answer 9

1) explain results of genetic screening , including consequences of a disease
2) discuss treatments available for genetic condition
3) discuss lifestyle choices / precautions that might reduce risk of a genetic condition developing
4) explain probability of condition / alleles being passed onto offspring - enable patients to make informed decisions about having children

Question 10

what is personalised medicine

Answer 10

• medicine tailored to an individuals genotype / DNA
• increasing effectiveness of treatment

Question 11

evaluate the screening of individuals for genetically determined conditions and drug responses

Answer 11

For :
- Some people could be heterozygous/ carriers e.g 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 :
• screening for incurable diseases or diseases that develop later in life may lead to depression
• may cause undue stress if patient does not develop didease
• could lead to discrimination by insurance companies / employers
• many diseases are rare
• Many are caused by many genes so would need too many probes ( expensive )