genome projects + gene technology 3.8.3, 3.8.4.2, 3.8.4.3

what are the different techniques for dna fingerprinting and diagnosis

pcr, gel electrophoresis, dna probes, hybridisation

what is a dna probe

short single stranded length of dna with an identifiable label attached e.g. radioactive labels that can be detected with an x-ray film or fluorescent labels that emit light under certain conditions, can be made out of single strand of nucleotides that are complimentary to the target allele

how are dna probes used in locating specific genes e.g. mutant allele for genetic screening

determine base sequencing through dna sequencing or database if seen before, develop dna probe that is complementary to mutant allele with label, copy dna probe using pcr, denature dna being tested with heat then cool with dna probe, wash of unattached probes leaving only hybridised ones, shine uv lamp on fragments to enable fluorescence which can be seen under microscope

how to test for a genetic condition

use dna microarrays consisting of many dna probes fixed on glass slide, add donor dna to array so any comp dna sequences in donor will bind in certain places, allows simultaneous testing of many different disorders - bound dna with fluoresce on glass slide so can tell which genes tested positive for

importance of genetic screening in cancer

oncogenes = mutated tumour suppressor genes which no longer suppress cell division, if someone inherits these genes they have a higher risk of cancer, knowing this people may choose to adapt certain lifestyle choices

variable number tandem repeats

genetic fingerprinting relies on fact that eukaryotes have introns that often repeat a variable no of times in non-coding dna, no 2 individuals will have the same non-coding dna or number or length of repeats except identical twins, the closer related 2 people are, the more VNTRs in common they will have

uses of gel electrophoresis

forensics to identify if prints at crime scene and suspect match, how closely people are related by studying evolutionary patterns/phylogeny, to see if individuals are carriers of certain alleles, to confirm pcr is working properly

gel electrophoresis to identify how closely 2 people are related/forensic

short tandem repeats (str) found in non-coding dna between coding genes, re used to snip sections of these, snipped str amplified with pcr then run through gel electrophoresis which will separate them based on size, diff bands formed at diff distances way from start point

meanings of bands in gel electrophoresis

closer to starting point dna fragment is, larger the dna fragment, further away band moves, smaller the fragment, positions of bands do not give indication that dna is same, only that it is the same length (re used to cut particular fragments only to minimise this error), thickness of band is conc of dna fragment, thicker band = more of same fragment

method of gel electrophoresis/ genetic fingerprinting

extraction (dna extracted from sample), digestion (re cut dna into fragments), run gel electrophoresis to separate dna strands according to size using voltage, separation (immerse gel in alkali buffer to denature dna in single strand then blot with nylon and absorbent paper so dna fragments stick to nylon), hybridisation (hybridise samples on nylon using radioactive dna probes then wash off lose probes), development (cover nylon with xray film and wait for marks to appear where radiation detected, analyse position of marks against control sample)

limitations of gel electrophoresis

helpful to compare dna samples but hard to make definitive conclusions - scale can only get so magnified, smearing means bands hard to interpret, can’t conclusively say 2 samples are related

why did scientists first sequence the genome of bacteria not eukaryotes

bacteria have 1 circular piece of dna not associated with histones, bacteria have no non-coding dna portions

importance of genome sequencing

useful in personalised medicine and vaccines, useful in clearing oil spills, can identify phylogenetic relationships between organisms (ancestry)

how can determining the genome of viruses allow scientists to develop a vaccine

scientists can determine the proteome and identify proteins, they can then identify potential antigens to use in the vaccine

benefits of developing a complete map of the human genome

better understanding of interaction between genetics and disease, early diagnosis/treatment of diseases, production of mkre effective medicines, tracing ancestral relationships

limitations of human genome mapping

in more complex organisms, the presence of non-coding DNA and of regulatory genes means that knowledge of the genome cannot easily be translated into the proteome