Week FO, FO SHO Flashcards
Define allelic heterogeneity
Different mutations on same gene cause same disease (different mutations at same locus cause similar phenotype)
Which of these organ systems is not effected in CF? a) intestine b) male genital tract c) female genital tract d) hepatobiliary system e) exocrine sweat glands
c)
In CF, what are the 5 molecular consequences that cause the disorder at the CFTR level? Which allele is most common?
- no synthesis, block in processing, block in regulation, altered conductance, reduced synthesis - delta F508 is in 70% of cases- block in processing
What is the difference between dominant and recessive forms of FIGHD (familial isolated growth hormone deficiency)? What happens in dominant negative form?
- dominant: mutations yield altered GH proteins - recessive: reduced GH expression - dominant negative - mutant binds to normal form and inactivates it
Type II Osteogenesis Imperfecta is a dominant negative, perinatal lethal disease that expresses locus heterogeneity. What two mutations at different loci/genes cause this disease?
- COL1A1 on chromosome 17 - COL1A2 on chromosome 7 Alpha 1/Alpha 2 proteins are mutant and lead to protein suicide
Type I Osteogenesis Imperfecta is a less severe, more common form that affects 1/5000 individuals. What mutation causes this disease?
COL1A1 on chromosome 17 that causes loss of expression or rapid degradation of mutant alpha-1; normal collagen formed but only 50% of normal level
Hemophilia A and Hemophilia B express locus heterogeneity. WHy is it important to know the type?
clinically indistinguishable, type affects treatment
In congenital deafness pedigree, why were all children of affected individuals not affected?
They were double heterozygotes - inherited two different mutations that cause same disease (locus heterogeneity)
What is the difference between achondroplasia and diastrophic dwarfism in regards to inheritance pattern?
Achondroplasia - auto dominant, 7/8 cases sporadic Diastrophic dwarfism - autosomal recessive
Charcot-Marie Tooth DZ: CMT1A is autosomal _________ while CMTX is X-linked.
dominant
Difference in modes of inheritance in male pattern baldness?
X-linked recessive OR Autosomal dominant (male sex influenced)
Define non-penetrance
when a genetic trait present in a genotype does not manifest the phenotype
Retinoblastoma is an autosomal dominant disorder where 40% of cases are familial. Explain the “two hit” process in RB and why 10% of obligate heterozygotes are non-penetrant
Two hits - need two hits in same cell to cause disease In familial, inherit one of the hits, only need 2nd hit. 10% of carriers never get second hit.
Describe how to incorporate penetrance into probability calculations
Multiple proportion of penetrance (or non-penetrance) by probability of passing gene down in each applicable step
True or false: A disease cannot have both non-penetrance and variable expressivity
False, totally can
While penetrance is ___________, variable expressivity refers to __________
all-or-none, extent
Neurofibromatosis type I (NF1) is autosomal dominant and an example of a disease that shows variable expressivity. Describe symptoms and occurrence/recurrence.
- 1/2 of NF1 are due to spontaneous new mutations - affects 1/3K - most (2/3) only have mild cutaneous involvement - sx include cafe-au-lait spots, lisch nodules, few neurofibromas - mildly affected parent can have a severely affected child - severe: 100s of fibromas, optic gliomas, learning disabilities, HTN, scoliosis, malignancies
Marfan Syndrome is an autosomal dominant connective tissue disease affecting 1/10K-1/20K that exhibits variable expressivity and pleiotropy. Explain.
- all affected individuals in one family have identical mutation in fibrillin gene, but will have different manifestations - Severe: aortic dilatation, pectus scoliosis, ectopia lentis - Mild - mitral valve prolapse, joint laxity, arachnodactyly, myopia - affects skeletal muscle, eye, heart
Describe pleiotropy
Diverse effects of a single gene on several organ systems and functions
In Osteogenesis Imperfecta II, all mutations are new mutations. What may be an exception in terms of inheritance?
germline mosaicism
If homozygous dominant, achondroplasia is _____________
perinatal lethal
In DMD, rate of loss of alleles in each generation is _____. In achondroplasia this number is ____
1/3, 7/8
Why is the rate of loss for alleles low in Tay Sachs and Cystic fibrosis?
autosomal recessive, affected make up small portion of compared to carriers
In germline mosaicism, a new somatic mutation occurs during embryogenesis in germline progenitor cells of one of parents. The recurrence risk in a family is equal to what?
the proportion of germ cells in parent that carries the mutation
Germline mosaicism plays an important role in recurrence risk in DMD. Describe.
in de novo cases, RR is 1-5% due to possible germline mosaicism. in DMD and hemophilia, spontaneous new mutations cause 10-20% of disease
Huntington’s disease is an autosomal dominant disease that is 100% penetrant and affects 1/20K people of European descent. Describe.
Loss of motor control, dementia between 30-50 Delayed age of onset
DNA cleavage by restriction enzymes facilitates isolation and manipulation of genes. The phosphodiester backbone is digested and produces palindromic type based on overhangs: ___, ___, ___
3’, 5’, blunt end
Nucleic acid hybridization identifies DNA/RNA on basis of binding to complimentary sequences. It is very sensitive, selective, and specific. Probes must be _________
single stranded
Describe in-situ hybridization
Reveals position of or location of gene on a chromosome, reveals distribution, can be done with intact cell/chrom/tissue
Describe the differences between Southern Blot and Northern Blot
Both are hybridization techniques - Southern Blot - DNA, requires restriction enzyme digestion, can be used for DNA library screening, identification of methylation sites, RFLP genetic analysis, detecting SNPs - Northern Blot - RNA, NOT Quantitative, used to observe gene expression, determine transcript size, map intro/exon positions, identify isoforms
Describe microarray hybridization technique
Glass slides with probes that identify each gene, fluorescently labeled
DNA cloning uses cloning vectors and PCR. What two enzymes are required?
Restriction enzymes and DNA ligase
What are the features required for a vector in DNA cloning? (3)
origin of replication multiple cloning site (restriction sites) ABX resistance gene (selectable marker)
DNA cloning produces two types of DNA libraries. Describe differences.
gDNA - chromosomal DNA, digested then fragments can be cloned cDNA - DNA transcribed to RNA then reverse transcription then DNA cloned
Describe temperature steps for PCR
1) Denaturation (94C) 2) Annealing (depends on primer) 3) Extension (72C)
Real time PCR uses fluorescent probes/dyes to detect and quantify ____ in real time
DNA, if reverse transcriptase used, can quantify mRNA
Which of the following is not a use of PCR? a) genetic testing b) clone gDNA c) forensic/identity screens d) identify translocation
d)
What is analyzed in Western blot and how?
proteins, travel based on molecular weight
Regulated gene expression uses a ______________ to turn genes on and off
genetic switch
miRNA and siRNA both cleaved to mature form by _______
dicer enzyme
miRNA is _______ expressed while siRNA is ________ expressed
endogenously, exogenously
Describe the mechanism of interference by siRNA
dsRNA processed by dicer –> siRNA comes with RISC –> RISC cleaves siRNA duplex –> RISC activated –> RISC guided to target DNA strand and cleaves
What are the four requirements for DNA sequencing?
free 3’OH group, DNA polymerase, primer, template
Describe Sanger sequencing
ddNTPs incorporated to initiation chain termination - no free 3’ OH end
How would this gel (result of sequencing) be read?
From bottom up (ATGCT etc)
Describe an antisense molecule
Bind to specific complimentary sequences and inhibit gene expression
Automated sequencing accelerated the human genome project. What is the major limitation of this and how is it overcome?
LIMITATION = only short sequences can be obtained in a single rxn
Overcome by shotgun sequencing - gDNA broken into fragments then sequence rebuilt
Shotgun sequencing leads to creation of genome maps. Describe the difference between genetic and physical maps.
Genetic maps produced by genetic techniques
Physical maps produced by molecular bio techniques
- includes restriction mapping, FISH, and STS mapping (positions of unique sequences)
Genome mapping shows genes and DNA markers such as SNPs, ssLPs and RFLPS. Describe RFLPs.
Restriction Fragment Length Polymorphisms= result from polymorphic restriction sites. Important for genetic testing to indicate disease locus, can analyze via Southern Blot or PCR
Describe homologous recombination in producing transgenic animals
Plasmid vector construct identical except for TK and target gene which produces target locus after homologous recombination. Southern blot will show proteins.
Describe Cre/IoXP use in site specific recombination and conditional gene targeting
Targeted gene floxed in between two recombinase binding sites such as IoxP, Cre is recombinase that can eliminate gene under certain conditions (tissue, time)
Pronuclei injection can also be used to generate transgenic animals. Describe.
Desired gene injected into fertilized egg –> egg implanted
Describe the two components of CRISPR gene editing
Cas9 protein - molecular scissors
guide RNA - guides cas9
Double strand breaks caused by Cas9 can be repaired in two mechanisms. Describe.
Non-homologous end joining = disruption in reading frame of gene of interest
Homology directed repair = sequence of interest flanked by homology arms is knocked in