L2 - Genetic disorders 1 Flashcards
what are the 2 types of genetic disease
germline:
mutations in DNA of reproductive cells causing INHERITANCE to every cell of offspring body
somataic:
mutations after conception in any cells that are not sperm/egg
= not inheritred or passed on
what percentage of peoiple will get cancer in their lifetime
1/3
briefly define genotype and phenotype
geno:
genetic makeup of the organism
phone:
physical charecteriscs of organism
some genes do not code for proteins but instead RNAs - give spme examples
non-protein coding RNAs:
- miRNAs for regulation of gene expression
- snrNAs - mRNA splicing
classical/forward and reverse genetics are 2 ways to identify genes that acuse disease - describve the 2
forward:
using an observed phenotype/trait work to identify the gene responsible
phenotype –> gene
reverse:
start with a known gene and study what happenes when it is disrupted/mutated to identify the phenotype
gene –> phenotype
what is positional cloning
identifying a disease causing gene by first locating its postion on a chromosome
- look for genetic markers/traits inherited with the disease that we’re looking for
= linkage analysis suggests that OUR gene must be close to these known genetic markers
= uses info on neigboring genes to find our gene
- this narrows down the region we shpuld search in - ‘mapping’
- identify all the candidate genes in this area from databse and sequence to identify which gene is responsible
what is linkage analysis and what is it good for
identifies genes that are inherited together due to being close together/same chrmosome
= ‘genetic marker’ that is co-inherited with our disease gene
GOOD for identifying traits strongly influenced by a SINGLE gene = multiple influencing genes gets confusing
what type of disorders are genome-wide ascociation studies (GWAS) good for identifying
polygenic disorders
= multiple influencing genes
what are genome-wide asociation studies
scan the entire genome of many individuals ( to find genetic variations that are common in people with a particular disease/trait
= good for polygenbic disorders
= linkagae analysis studies inheritance in famiulies/people related to one another to identify single gene disorders
what are polymorphic markers and how are they helpful in identifying genetic disorders
specific spots/loci in DNA where genetic variation is common
= act like genetic “flags” that help locate genes linked to diseases
by looking at inheritance and seeing which offspring had the disease and inherited which markers = we can locate the location of disease gene
name 1 type of polymorphic markers
micro or minisatelite regions = repeats in the DNA
= different people have different numbers of these repeats
Find the location of a disease-causing gene by seeing how often the polymorphic marker is inherited together with the disease
describe gene mapping PRE-genome project
- create regional genetic map = see which ‘markers’ are inherited with observable disease trait
2.created genomic library of clones from the genomic DNA = each plasmid/clone contains a differenr fragment of the DNA
- select for the clones with the markers that WE have identified being close to the disease gene (hybridisation of probe)
- produce a contig –> stitching together the overalpping sequences from the selceted clones to produce a sequnce that is responsible for disease
- search within this seqeunce for the actual CODING regions of DNA and excluding the polymorphic markers
what is a contig
pieced together overlapping regions of DNA to produce one ‘continous’ sequence
difference between physicala dn genetic map
- genetic map is the distances between genes based on recmobination evenst
= genes that are more likley to be inherited together are ‘closer’ in the genetic map but this does NOT mean they are physically close
- physical map is based on the ACTUAL physical distance between 2 loci - nucleotides between them
describe how gene mapping post-genome project can be done with human genome project
- identify where on the chromosome disease gene is by studing linkagae analysis of families with polymorphic markers
- once aprox loci of gen on chromosome is found –. look at ALL genes in that area in database (from human genome project)
- Candidate genes can be tested for
= sequence analysis to identify any mutations and compare to a healthy persons sequence
= expression analysis (RNA-seq) to see activity of genes in area
when was the human genome project completed
April 2003
= used snger sequencing
name 2 types of next-gen sequencing methods used that are more efficient than Sanger
illuminana:
sequence by synthesis with ddNTPs –> produce flourescent dots to correspond to specific base
= nit very long reads
Nanopore sequncing:
protein pore with DNA strand fed through –> electric current shows which base is in pore at that time
= very long reads but error prone
difference between euploidy and aneuploidy
euploidy is having abnormnal numbers of sets of chromones –> 3n instead of 2n
anneuploidy is abnormal number of individual chromsomes –> 2n + 1
describe what cytogenitic analysis is
identififdcation of cells going through different stages of mitosis sby staining
= centrifuge cells and stain –> view under microscope
what is karyotyping
examines chromomes for abnormalities
= anneploidy
banded karotyping canb be done to show more subtle changes like differences in genes
what is FISH
Flourescence in situ hybridisation
= does a whole chromosome ‘paint’ to easily show mutations
complimnetary flourescent DNA probe binds to sequence = can have specific probes for certain genes
name the 3 anneuploidy trisomies
T21 - down syndrome
T18 - Edwards
T13 - Pataus
= anneuploidy NOt euploidy as its a difference in a single chromosome not abhwole set
what are chromosmal trimoy anneplodies due to
random non-disjunctive errors in meiois of oocytes
= chromsoosmes fail to seperate
= egg/gamete gains an extra copy of chromosome
what percentage of pataus and edwards syndrome patients die in first year
90%
= congenital heart defects for edwards
