Genetic variation Flashcards
What are alleles?
- different forms of the same gene
- usually dominant or recessive
- some are phenotypic
- can predispose people to disease
What are autosomal dominant alleles?
will express itself in the phenotype of a heterozygous individual, eg huntingtons
What are autosomal recessive alleles?
both parents must be at least heterozygous for condition, is most common if parents are related
eg sicle cell, CF
What are X-linked recessive alleles?
most often expressed in males, females must be homozygous
eg haemophilia, colour blindness
What are single nucleotide polymorphisms?
DNA sequence variation of a single nucleotide at same position in genome between members of the same species
What 3 things can SNPs cause?
- changes in amino acid codon > altered codon function
- affect levels of expression of protein
- affect where/when protein is expressed
What is the one requirement to properly classify an SNP?
- ## sequence variation must be found into at least 1% of the population
What are SSRs?
Simple sequence repeat - tandem repeat of 2-8 base sequences
What is pharmacogenetics?
influence of an individual’s genetic variation on response to medicines
- may be due to difference in expression levels of proteins
- different gene sequences
What is pharmacogenomics?
- studying drug interactions with multiple genes in large patient groups
What is personalised medicine?
- individuals screened for commonly occuring SNPs
- SNP profile used to develop patient specific profile for response to specific drugs
- informed drug choices
What are the 6 advantages of personalised medicine?
- more powerful medicines - targeted, maximising affects
- moving away from one-size-fits-all approach
- better screening for disease
- improvement in drug discovery and approval
- better vaccines
- overall decrease in healthcare costs
What are the 4 normal control mechanisms to prevent mutation?
- Heterozygosity: two copies to minimise loss of funtion due to mutation
- Apoptosis: damaged cells killed to prevent transmission of mutated genes
- Cell cycle control: check points during cell division to ensure cells are healthy
- regulation of gene transcription: requirement for appropriate activation signals to induce gene expression
What are the three risk factors for mutation?
- environmental
- chemical (smoke)
- radiation (UV)
- inherited
- mutations in germline
- viral
- rous sarcome virus
- HPV
What are 2 the types of sequence mutations?
- deletions or insertions
- single base mutations
What are inherited mutations?
monogenic diseases
- cystic fibrosis
- sickle cell anaemia
- X-SCID
What are oncogenes?
- mutated forms of normal cellular genes that control cell growth
- usually dominant - only need mutation in one allele to increase function
- oncogenes usually encode growth factor, receptor, signal transducers or nuclear transcription factors
What are epidermal growth factors? (EGF)
- important proto-oncogenes involved in many cancers
- EGF is important, drives cell proliferation
- intrinsic kinase domain leading to activation of downstream signalling pathways
What 4 things can mutations of EGF receptors cause?
- ligand dependence
- consititutive dimerisation
- overexpression
- gene amplification
What are tumor suppression genes?
- exert negative effects on cell growth
What is the result of mutations on tumor suppressor genes?
- mutations inactivate them and promote aberrant cell growth
- usually autosomal recessive - require loss of both alleles
What are translocations?
- aberrant cross-overs between chromosome during cell division
- can lead to cells becoming separated from this and instead controlled by another
- can dysregulate gene expression may lead to alterations in cell growth
How does lung cancer develop?
- mutations commonly caused by environmental carcinogens, particularly those in cigarette smoke
- 60% of lung cancer cases involved p53 mutations
- benzo(a)pyrine in cigarette smoke in metabolised in liver, generating a potent mutagen
What is eukaryotic gene regulation?
- controlled expression of a gene in a temporal and spatial manner
- important for specialised function
- most common mechanism for gene regulation
What are promoters?
- DNA sequence which determines the site of transcription initiation for an RNA polymerase
- composed of set of conserved DNA sequences
- present in DNA upstream of transcriptional start
- recognised by transcription factors and polymerases
What is the gene transcriptional process?
- driven by availability/activation of transcription factors
- accessibility of DNA
- chromatin structure - DNA + histone proteins
- requires co-activation proteins to unwind
What is histone acetylation?
- histone proteins contains many basic amino acids with +ve change
- enables interaction between with -ve phosphate backbone of DNA
- acetylation blocks ability to bind DNA by masking +ve change
- relaxes interaction of DNA with nucleosome
- uses histone acetyle transferases (HAT) and histone deacetylase (HDAC)
What is chromatin?
- heterochromatin
- densely packed nucleosomes
- not actively transcribed, deacetylated histones
- euchromatin
- extended ‘beads on a string’ appearance
- being actively transcribed, acetylated histone
How common is CF?
1 in 25 are carriers
1 in 25,000 live births are affected
What is the most common cause of death in CF sufferers?
Lung dysfunction and infection
What is affected in CF sufferers?
Impaired function of organs with secretory function
How is the pancreas affected in CF?
- lack of pancreatic enzyme secretion
- reduced insulin
How is the digestive system effected by CF?
- meconium ileus + obstruction
- failure to thrive in newborns
What are the 3 ways you screen for CF?
- immunoreactive trypsinogen (IRT) - guthrie test
- all newborns in uk
- trypsinogen made by pancreas and secreted into gut
- elevated in blood/
- genetic screening
- IRT positive + siblings are then screened for mutations
- sweat test
- elevated skin Cl- levels
- below 30mM CF not likely
- above 60mM CF likely
- elevated skin Cl- levels
How is nutrition mananged in CF?
- formerly the most common cause of death in CF
- nearly all patients have pancreatic insufficiency
- lack of pancreatic protease, amylase and + lipase
- unable to digest food properly
- managed by diet + enzyme supplement
- pancreatin
- lipase, protease, amylase
- usually porcine
- inactivayed by capsules
- enteric coating
How are the lungs affected by CF?
- chronic infection
- mucus plugging
- structural changes
- massive neutrophil infiltration in airways
- failure to clear bacteria and dying neutrophils
- inflammatory to airway tissue
- decline in lung function
- epithelial damage