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Molecular Genetics and Microbiology
Johanna Rommens

Genomic approaches to Some individuals with Clinical cytogenetics Look at chromosomes and banding patterns Constitutional cytogenetics – chromosomes born with – present since conception Overview of G-banding procedure Take blood Cochicine arrests metaphase Hypotonic solution – swells cells – cells explode; chromosomes spread across slide – chromosomes look like black bands if use certain enzymes to treat them, digests certain chromosomes away – G banding pattern – take picture on computer – G-banded chromosomes – each chromosome has its own distinctive banding pattern – looking for differences in banding pattern between two homologous chromosomes If extra band in one of the homologs, tells you there is abnormality Unlike sequencing, with small piece of DNA to sequence; this is low-resolution whole view of the genome so can see what’s going on – can detect extra copies of chromosome missing – not very high- resolution If there is translocation (if small part of chromosome 17 attaches to chromosome 15) – break in rearrangement and this can be significant because can split a gene in half – in cancer, can activate expression of genes that active tumourgenesis If a child is missing that much DNA in 18 – typically cause of child’s condition To confirm: every time if you look at parents, their chromosomes are normal – typically de novo events Constitutional chromosomal disorders When a child with abnormal development – clinical geneticist tires to think of list of potential chromosome regions affected that could cause child’s symptoms Can only see large deletions/duplications – missing small ones because resolution not high enough Do FISH – targeting one pspecific part of chromosome – high resolution not available by G-banding Make DNA probe that the nucleotides specific to that part of chromosome – because of human genome project – not only was it important that it sequenced genome, allowed development of tests – allowed probe for any region of genome to look at – easy to find probe and fish for any region of genome to look at This probe is labeled with fluorescent dye – basically shows signal pattern Deletion that causes George Syndrome – hybridize with fluorescent probe Green is control probe – to make sure hybridization worked Disease region, red probe, is deleted from one of the chromosomes – but when look at G banding, this is normal Take blood sample from patient, chop up DNA into fragments, label with red fluorescent dye so patient’s DNA is red; DNA from healthy people; 1 to 1 ratio of green and red; hybridize to glass slide with probes, each representing piece of chromosome, so entire genome covered; if there is deletion in patient, get excess of green for that specific part of chromosome Ratio of red is higher than green so that means duplication in the picture – deletion – Very accurate because so many probes, know exactly where deletion and duplication is Zoom in on region – Normal variation in population: copy number changes are normal variation Sub-microscopic copy number variation – basically done microarray analysis and show regions of genome where there is deletions and duplications in healthy individuals Liely to be benigh variation Same genome browser but it has a track where it has each one of these studies – if study had shown duplication Probably 50% of peopl
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