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21 Cards in this Set

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Implications of meiosis
-2 copies of autosomal genes 1 from mom and 1 from dad
-if parent is hetero then ea. kid has a 50/50 chance of getting 1 or the other allele
-genes on separate chromos assort independently
-when 2 genes are on the same gene they are linked (no indep assortment)
-it can be broken by crossing over and also applies to suff other than genes i.e. SNPs restriction polymorphisms,VNTRs
Haplotype
set of linked genes/markers on the chromo (when genes are linked)
linkage disequlibrium
-non random assortment b/t 2 alleles on the chromo
-linkage focuses on a locus
-diseq. focuses on an allele
Single gene disorders
-disease causing alleles arise in new germline mutations
-if dominant, cause disease immeadiatley after they arise
- if severely dominant natural selection removes
-Recessive are time bombs
-they are carried through generations un-noticed then cause disease in a homozygote
-natural selection ignores them if a heterozygote and allow them to be common
AD inheritence
- pt.s are heterozygotes
-male and female are affected equally
-their kids have a 50/50 risk of getting disease
-affected offspring have affected parents
-disease doesn't skip gens
- unaffected people don't carry the gene
-rare for 2 heterozygotes to meet
-new mutations are common and dec penetrance
-severe dominant mutations are caused by new mutations
Achondroplaisa
-AD,single gene
-linkage ocan be found on chromo 4 and 12
-1:10,000; 80-90% new mutations
-allelic heterogeneity
-Point mutation in FGF receptor 3 (FGFR3) expressed in chondrocytes
-Trait shows full penetrance and little variability
-paternal age increases risk for new mutations
Symptoms:
-dysmorphic dwarfism
-short limbs
-lumbar lordosis
-prominant forehead
-norm trunk
-small nose/low nasal bridge
-homozygotes die @ birth
Problems w/ counsiling:
ACH homozygotes or ACH/HCH compound heterozygotes are as badly off as TD patients
the most common form of short-limbed dwarfism
Aperts
-1:10000
-mutations in the gene for fibroblast growth factor receptor (FGFR2)
-Craniosynostosis (abnormal fusion or cranial structures)
-AD
-Mental deficiency
-hearing loss
-syndactyly
-cardiac septal problems
Hypochondroplasia
(HCH)
-AD
-Often inherited
Mutations in FGFR3 gene
-Allelic heterogeneity
-prominant forehead
-hypoplaisa of mid face
-norm body size
-small hands
-norm intelligence
-narrowing of spinal canal
Thenatophoric dysplasia (TD)
-AD
-All cases of TD are result of new mutations in FGFR3 gene
-Allelic heterogeneity
-Misshapen head
-severe platyspondylia
-almost always results in neonatal death
-narrowing of spinal canal
-very short ribs
Duchenes Muscular Dystrophy
-XR
-1/3 cases involve new mutations
-1:4000 male births 60% due to deletions one of the dystrophin gene largest genes characterized of the X chromosome should be high in skeletal and cardiac muscle
-Maintains muscle membrane
structure
-Mutations in the Dystrophin gene partial deletions most common with a variety of point mutations
-early childhood onset
-muscle wasting starting at 1-2 years
-wheelchair bound by 10-12 years
-die by 16-20years due to respiratory cardiac failure
-characteristic is Large fatty calves
-dx by deletion scanning oe linkage,PCR,Southern Blot,inc Creatine kinase
-females have an inc risk and have more musc weakness


-
Ohter muscular diseases
Beckers:
-XR
-mild mut. in dystrophin gene
Limb girdle:
-AR
gene products interact w/ dystrophin
Skewed X chromosome inactivation
-carriers of an X linked disease will show symptoms if X inactivation is skewed or have more of 1 parents X active
-reasons for skewing are random
-can be local so symptoms are seen in only 1 tissue/region
-one X has a deletion which leads to cell death in the cells that have this chromo active
-is also caused by inactivation of translocated autosomal material that causes cell death
-X inactivation doesn't spread through nautosomal material
Anticipation
-genetic diseases that show an earlier age of onset and more severe expression in the more recent generation of a pedigree
-occurs in triplet repeat disease b/c inc # of repeats leads to a more sev. phenotype/earlier onset
-the repeat # inc in meiosis only or mostly in 1 sex
Trinucleotide repeats
-natural occuring seq in 3 bp's that are repeated
-probs happen when these are long
-if above the length sequences become unstable and lead to a premutation
-also the exp. or fnx of the product changes leading to a full mutation w/ symptoms
-can determine length by PCR (could be too big) or Southern blot
Other triplet diseases
-most have CAG repeats in the exon
-dystrophia myotonic has a CTG repeat is AD
-Fredreich ataxia has GAA repeat in intron AR
-fragile X has CGG repeat X linked
Huntingtons
-AD
-1:20,000
-CAG trinucleotide repeat expansion in genes coding for glutamines called huntingtin
-10-30 CAG repeat is normal
36-121 causes HD
-Fragment of protein precipitates binding inhibitors of histone acetylation
-anticipation occurs
-neurodegenerative disorder
-progressive
-personality change
-memory loss
-involuntary motor problems
-early onset when disease is inherited paternally
-37 years is usual age of onset but 100% penetrance by 80 years old
-earlier onset/more severe phenotype when repeat number increases
-homozygotes and heterozygotes equally affected l
-lowest mutation rate of any known locus (for repeats under 20)Woody Guthrie
Myotinic dystrophy
-1 in 10,000
-AD w/ anticipation
-Tandem Repeat Expansion - CTG amplification at the 3’ gene for myotonin kinase
-normal individuals show 5-30repeats
-Myo Dys 50-1000 repeats
-if more than 50 in females then is unstable=anticipation
-wasting of sternomastoid and facial musc. and distal limb musc
-cataracs
-cardiac arrythmias
-variable severity
-
Fragile X
-1:2000 male births
-cytogenic fragile site on X chromosome
-unstable CGG trinucleotide repeats in the 5’of the FMR1 gene (upstream of start site)
-FMR1 becomes hypermethylated and transcription is suppressed
-usually occurs during
-female meiosis
-exclusively repeat expansion when inherited through mother
-males carrying more than 230 repeats are affected with increasing severity (up to 2000)
-female carriers that carry full mutation dec IQ.
Fragile X symptoms
-moderate to severe mental retardation (variable)
-Big ears
-Prominent jaw
-High pitched speech
-Protruding forehead
-Coarse facial features
-Unusually large testis
-Most common form of moderate mental retardation
Complications w/ gene expressivity
-incomplete penetrence: pt. has genotype for disease but dosen't show the phenotype, kids can be affected i.e. retinoblastoma
-variable expression: shows penetrence, but severity differs greatly,a parent can have a mild exp. and kid can have a bad exp.
Continued
-Locus heterogeneity:mutations in diff genes causes same phenotype,1 disease pheno can be caused by muts in diff loci in diff families
-allelic heterogeneity:
variable exp cand be caused by diff types of muts at the same disease locus(diff muts in the same gene
-phenocopies:
conditions that look like genetic diseases but are caused by nongenetic factors
-pleiotropy:
genes that have more than 1 effect on the body i.e marfan,CF
Imprinting:
differential activation of genes depending on which parent they came from ,several genes in a critical region are active on 1 chromo if the active copy is deleted b/c of mut. then disease occurs
-contiguous disorders:
some syndromes involve the deletion of adjacent genes to those of the disease,micro del and micro duplication