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21 Cards in this Set

  • Front
  • Back
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
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
-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
-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
-mutations in the gene for fibroblast growth factor receptor (FGFR2)
-Craniosynostosis (abnormal fusion or cranial structures)
-Mental deficiency
-hearing loss
-cardiac septal problems
-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)
-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
-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
-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
-mild mut. in dystrophin gene
Limb girdle:
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
-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
-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
-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
-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.
-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
conditions that look like genetic diseases but are caused by nongenetic factors
genes that have more than 1 effect on the body i.e marfan,CF
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