[21.4] locating genes, genetic screening, and counselling Flashcards
what is a DNA probe?
a short, single-stranded length of DNA which has some label attached that makes it easily identifiable
what are the 2 most commonly used probes?
- radioactively labelled probes - made up of nucleotides with the isotope ³²P, which can be identified using an X-ray film exposed by radioactivity
- fluourescently labelled probes - emit light under certain conditions eg. when probe has bound to target DNA sequence
how are DNA probes used to identify particular genes of alleles? (5)
- DNA probe is made with base sequence complementary to part of base sequence of DNA that makes up allele of gene we want to find
- dsDNA being tested is separated into its two strands
- separate DNA strands are mixed with the probe
- probe binds to complementary base sequence on one of the strands (DNA hydridisation)
- site at which probe binds can be identified by radioactivity or fluorescence that probe emits
what is DNA hydridisation?
when a section of DNA or RNA is combined with a single-stranded section of DNA which has complementary bases
how does DNA hydridisation happen?
- dsDNA is heated to separate it into its two complementary single strands
- if other complementary sections of DNA are present in the mixture as it cools, they will combine with the separated DNA strands
- this is just as likely as the two strands recombining with each other
what is the importance of genetic screening?
- hetereozygous recessive alleles will not display symptoms of disease but still carry mutant allele so have capacity to pass it on
- can determine probability of a couple have children with a genetic disorder based on family history and genetic screening
- can detect oncogenes - individual at greater risk may make lifestyle changes, check more regularly or undergo surgery to reduce risk
how is a specific allele of a gene located using DNA probes and DNA hydridisation? (9)
- sequence of nucleotides on mutated gene is determined by DNA sequencing or found in genetic libraries
- fragment of DNA produced with a sequence of bases complementary to mutant allele we are trying to locate
- multiple copies of DNA probe formed using PCR
- DNA probe made by attaching marker to DNA fragment
- DNA from person with suspected mutant allele is heated to separate its two strands
- separated strands cooled in mixture with many DNA probes
- DNA washed clean of any unattached probes
- remaining hydridised DNA will now be labelled by probe
- label on probe detected, indicating presence of genetic disorder
what is personalised medicine?
when doctors provide advice and healthcare based on an individual’s genotype
what is genetic counselling?
when advice and information is given to enable people to make personal decisions about themselves or their offspring
what is are the advantages of genetic testing and ways it can be used? (9)
- could test for diseases so result in early treatment of diseases
- patient could change lifestyle to reduce risk of developing multifactorial disease
- carrier screening - making informed decisions about whether to have children
- pre-implantation genetic diagnosis as part of IVF
- prenatal diagnostic testing
- newborn baby testing
- forensics and identity testing
- improving quality of life
- preventing children being born with life limiting diseases
what are the disadvantages and things to consider with genetic testing? (12)
- ownership of genetic information and its misue
- risk of false positive or false negatives
- discrimination and social stigmatisation
- effect of finding out probability of late onset disorders
- affect ability to get life insurance, hired for particular jobs, pension etc.
- affect people’s choices to adopt children
- how will genetic tests be evaluated and regulated for accuracy and reliability
- how do we prepare the public to make informed choices
- uncertainties associated with gene tests for susceptibilities and complex conditions linked to mulitiple genes and gene-environment interactions
- if testing should be performed if there is no treatment available
- if parents should have the right to have their children tested for adult-onset diseases
- if patening DNA sequences limits their accessibility and development into useful products
