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42 Cards in this Set
- Front
- Back
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Define locus
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Region of a chrom where gene is located
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Define allele
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Alternative form a gene occupying same locus
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Difference between heterozygous and homozygous.
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Heterozygous: person with 2 different alleles on each chromosome from different parents
Homozygous: same allele on each chromosome from each parent |
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How many mutant alleles are required for a an autosomal dominant allele to be expressed?
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Only one mutant allele required
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What is variable expressivity? Example.
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Variation in expression of a disorder within a single pedigree (family); one person can be more affected than another even in same family
Ex: NF-1 |
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What is variable penetrance? Example.
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Percent change that carriers of disease mutation will exhibit phenotypic signs and symptoms of disorder.
Some people with the dz phenotype will express and others won't Ex: BRCA |
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What is age-related penetrance? Example.
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Disease phenotype only recognized with age
Example: NF1 |
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What is complete penetrance? Example.
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If you have the mutation, you have a 100% chance of showing dz phenotype.
Ex: Achondroplasia |
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What is locus heterogeneity? Example.
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Different genes on different chromosome cause similar versions of disease
Ex: OI (I, II, III, IV) |
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What is the paternal age effect? Example.
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Change of new mutation with increased paternal age
Ex: Achondroplasia |
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What is a new mutation rate?
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Occurrence of disease due to de novo mutations
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Marfan's
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AD
Usually have family hx pectus carinatum (chest sticks out) pes planus (flat footed) arachnodactyly (tapered, long fingers) Ectopia lentis Myopia (near sighted) MV Prolapse Aortic Dissection |
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Citrullinemia
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AR
Elevated ammonia, citrulline (urea cycle disorder) |
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Neurofibromatosis I
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AD
Cafe au lait spots Freckling Lisch nodules VARIABLE expressivity Age-Related penetrance |
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Osteogenesis Imperfecta
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AD
Classical I: bone fragility, bowing, BLUE SCLERA II-III: usually lethal (II may be survivable) IV: Milder; WHITE sclera |
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Achondroplasia
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AD
Rhizomelic shortening of limbs Short Stature Trident hands Mostly DE NOVO Possible family hx |
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Duchenne Muscular Dystrophy
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X-linked Recessive
Delay in walking, muscular deterioration; fatal |
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Germline mosaicism. Example.
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OI II (achonrdo too)
De novo mutation in egg/sperm |
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Resproductive fitness. Ex with OI II.
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Reproductive fitness of 0 because it is LETHAL
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What is the founder effect?
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Increased prevalence of disorder due to shared ancestry of members of a population
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When is a parent an obligate carrier?
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When their child has phenotype of an AR disorder
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Difference between X-linked and X-linked lethal.
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X-linked: males survive
X-linked lethal: males miscarry or die early |
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What is favorably skewed X cell inactivation?
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unaffected females
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What is unfavorably skewed X cell inactivation?
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Carrier females with extra symptoms
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What are manifesting carriers of an X-linked disorder?
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Women with x-linked recessive disorder who are probably unfavorably skewing X inactivation
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What is triplet instability?
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Areas of DNA with triplet nucleotide repeats (ex: CGG, CGG, CGG) unstable past a certain number; can expand and lead to gene disruption
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What is genetic imprinting?
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at a single locus, an allele is either active/inactive depending on parents from which allele was inherited
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What is the effect of methylation on genes?
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Inactivates them
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What is uniparental disomy?
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Both members of a chromosome pair are inherited from one parents; neither from other parent
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What is genetic anticipation? What is it usually due to?
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GENETIC AMPLIFICATION
Increase in severity of phenotype in successive generations (usually because of triplet expansions) |
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What is the pattern of mitochondrial inheritance?
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Transmitted only through mother; all offspring may show signs of disease
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What is multifactorial inheritance? Examples.
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Multiple genes along with environmental factors cause particular trait of disease
Ex: HTN, asthma, DM, Autism |
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What are epigenetic differences?
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Differences in expression of DNA, not in sequence of DNA
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Fragile X Syndrome and repeat cutoffs.
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Long, thin face, large ears
MACRO-ORCHIDISM upon puberty Retardation, disability 0-45: No Dz 46-54: grey zone 55-200: Premutation 200+: FULL MUTATION |
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Can pre-mutation carriers of Fragile X show symptoms?
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Yes:
Men: FXTAS (early tremors) Women: Premature ovarian failure |
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Prader Willi Syndrome.
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Overeating, OCD
FAILURE TO THRIVE UNDESCENDED TESTICLE ALMOND SHAPED EYES Tantrums, Jig saw puzzles Esotropia (eyes turn in) Weight gain MILD MR |
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Angelman Syndrome
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Severe MR
no speech LAUGHTER Happy Puppet Syndrome |
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Prader Willi vs Angelman. Test to tell?
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PWS: deletion on PATERNAL 15
AS: deletion on MATERNAL 15 (mothers are angelic) Methylation testing FISH to ID dels |
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What are classic symptoms of mitochondrial disorders?
Pedigree patterns? |
Migraine, Depression, Bowel Dysmotility
Affected females transmit disease to ALL children Affected males DO NOT transmit dz |
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Friedrich's Ataxia
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AR, Multifactorial
GAA repeats, may even be mitochondrial |
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Pedigree patterns for:
X-linked AD AR Mitochondrial |
X-linked: NO MALE TO MALE
AD: Multiple generations, male to male! AND female to male! AR: No multiple generations Mitoch Dz: Only children of affected moms |
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Are women with x-linked diseases more or less affected than men with the same disease?
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Men are much more affected with the disease phenotype
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