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27 Cards in this Set
- Front
- Back
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What is Phenocopy?
Genocopy? |
BOTH REFER TO PHENOTYPE
Phenocopy – a phenotype produced by non-genetic causes, that is similar to a phenotype produced by genetic causes (caused by environment or genetic causes) Genocopy - similar phenotypes produced by different genotypes (caused by different genetic causes) |
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How can ambiguous genitalia in females be an example of phenocopy?
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can be due to being exposed to exogenous androgens in utero
OR virilizing 21-hydroxylase deficiency (either environmental or genetic cause!) |
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define
Allelic heterogeneity Locus Heterogeneity |
allelic: multiple mutations within the same gene can produce the same phenotype
locus: different genes have mutations causing the same phenotype |
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what are the following an example of:
Anemias caused by different mutations at the β-globin gene locus Over 1000 different CFTR mutations causing cystic fibrosis (delta 508 most common) |
Allelic heterogeneity - Similar phenotypes produced by different mutations at the same gene
(Form of genocopy) |
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what is the following an example of:
SCIDS Osteogenesis Imperfecta Ehlers-Danlos Syndromes Charcot-Marie-Tooth Disease Familial Parkinson Disease |
Locus Heterogeneity - similar phenotypes produced by mutations at different gene loci
(Form of genocopy) |
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what is the difference btw allelic heterogeneity and polymorphism?
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Polymorphism will not produce the same phenotype, whereas allelic heterogeneity would
polymorphism also has to have frequency above 5% |
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define Polygenic Traits
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phenotypes determined by multiple genes.
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what is meant by non-syndromic?
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the gene alteration only causes one problem (ex: causes deafness only, and not other symptoms)
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what is meant by pleiotropy?
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A single gene controls multiple traits
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Marfan syndrome is a mutation in what?
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fibrillin gene (chromosome 15)
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Tall Stature
Arachnodactyly Dolichostenomelia Myopia; dislocated lenses Aortic root dilatation; risk for aortic aneurysms what is this? mutation in? |
Marfan Syndrome
Mutations in fibrillin gene (chromosome 15) |
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What are the two forms of neurofibromas?
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plexiform: more neural tissue
dermal |
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pt presents with cafe au lait spots, and a bunch of pedunculated skin patches diffusely spread across the body...what does this pt have?
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Neurofibromatosis 1 (NF1)
Gene product: neurofibromin (a GAP) (also known as von Reklinghausen disease) |
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Genetic variablitly is commonly demonstrated by what genetic problem?
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Osteogenesis imperfecta
Differences in degree of the phenotype produced by the same genotype In general, autosomal dominant disorders tend to be more variable than autosomal recessive disorders |
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please describe Osteogenesis Imperfecta Types 1 & 2..include the underlying genetics
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both: Brittle Bone Disease (AD mutation of COL1A1/2 genes)
type 1: blue sclerae type 2: multiple interuterine fractures (more serious) |
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what is Incomplete or Partial Penetrance?
Example?** |
a mutation which does not produce a mutant phenotype in everyone who inherits the mutant genotype (Percentage of the pple who have the phenotype that actually show it...)
BRCA genes (AD-tumor suppressor genes) BRCA1 ~85% by age 65 years BRAC2 ~35% lifetime risk |
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Which BRCA gene is more likely to cause male breast cancer?
what about ovarian/bowel/prostate |
male breast: BRCA 2
varian/bowel/prostate: BRCA 1 |
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What is Codominance? classic example?
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Codominance - different alleles inducing independent effects on the phenotype
Blood groups |
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What is mitochondrial inheritance?
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Maternal Inheritance – transmission from mothers to all children regardless of sex, never transmitted from fathers to any children
note: within the mitochondria population you will have some that have the mutation and some that don't (this is known as heteroplasmy) |
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What is Anticipation?
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A mutant phenotype that increases in severity each generation
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Fragile X syndrome is an example of what genetic term
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Anticipation: A mutant phenotype that increases in severity each generation
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Pt has a mental retardation, but still maintains a moderate IQ. They also present with a long face, prominent jaw, and forehead. You notice the person is hyperactive and tends to flap his hands..what does he have? Genetics? Example of what genetic property?
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FRAGILE X
due to FMR1 Gene Anticipation: A mutant phenotype that increases in severity each generation Most common heritable mental retardation (moderate IQ***) Second only to Down Hyperactivity Hand flapping Biting Temper tantrums Poor eye contact After puberty long face*** prominent jaw and forehead*** large ears macro-orchidism (large testicles) |
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3 examples of trinucleotide expansion diseases?
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Fragile X
Huntington Myotonic Muscular dystrophy |
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how does anticipation occur in Fragile X syndrome?
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the first person has a number of CGG repeats
in the next generation you have even more copies of the CGG repeat by the third generation you might have >200 repeats this leads to methylation (inactivation) of the promotor, so you knock out the gene getting a serious defect |
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Epigenic imprinting is what? Key example?
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A mutant genotype with a different phenotype depending on context (e.g. the sex of the patient)
e.g. Prader-Willi and Angelman Syndromes |
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What is Prader-Willi Syndrome? (presentation and cause)
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Neonatal hypotonia/feeding problems (gradually improvement)
Obesity due to compulsive feeding (after 12-18 months) Almond-shaped eyes Hypopigmentation Upslanted palpebral fissures Bitemporal narrowing Mild MR/learning disabilities Behavior problems Small hands and feet Hypogonadism Small genitalia (penis/clitoris/scrotum/labia) due to paternal chromosome 15 (microdeletion due to methylation of the middle gene--genomic imprinting) |
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What is Angelman Syndrome? (presentation and cause)
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Happy disposition (paroxysms of laughter)
Severe mental retardation Jerky, ataxic movements and gait (puppet-like) Prominent mandible/pointed chin Wide mouth Arm posturing Absent speech Seizures Thin upper lip Widely spaced teeth Microcephaly Hypopigmentation due to maternal chromosome 15 (microdeletion due to methylation of outer genes--genomic imprinting) |
