Genetics

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bcl-2

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follicular and undifferentiated lymphomas

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erb-2

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breast, ovary, stomach cancer

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n-myc

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neuroblastoma

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ret

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MEN I/II

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l-myc

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small cell lung cancer

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what is pleiotropy?

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single mutation exerts multiple effects

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when are Barr bodies seen?

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any individual with 2 X chromosomes

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what is variable expression?

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nature and severity of phenotype varies from 1 individual to another

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what is incomplete penetrance?

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not all individuals with a mutant genotype show the mutant phenotype

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what is pleiotropy?

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one gene has more than one effect on an individual's phenotype

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whatis imprinting?

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differences in phenotype depend on whether the mutation is of maternal or paternal origin (e.g. angelman's - maternal; prader-willi - paternal)

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what is it called when a the severity of a disease worsens or age of onset of disease is earlier in succeeding generations?

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anticipation

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what is loss of heterozygosity?

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if a patient inherits or develops a mutation in a tumor suppressor gene, the complementary allele must be deleted/mutated before cancer develops - not true for ongogenes

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what is a dominant negative mutation?

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exerts a dominant effect - a heterozygote produces a nonfunctional altered protein taht also prevents the normal gene product from functioning

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what is linkage disequilibrium?

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tendency for certain alleles at 2 linked loci to occur together more often than expected by chance - measured in a population, not a family, and often varies in different populations

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what is mosaicism?

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occurs when cells in the body have different genetic makeup - e.g. lyonization - random X inactivation in females

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what is locus heterogeneity?

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mutations at different loci can produce the same phenotype (e.g. albinism)

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if a population is in Hardy-Weinberg equilibrium, then disease prevalence equals what?

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p2 + 2pq + q2 = 1

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if a population is in Hardy-Weinberg equilibrium, then what does allele prevalence equal?

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p + q = 1

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for Hardy-Weinberg - p and q are separate alleles: what does 2pq equal?

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heterozygote prevalence

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hypophosphatemic rickets is inherited in what manner?

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X-linked dominant - transmitted through both parents - either male or female offspring of the affected mother may be affected, while all female offspring of the affected father are diseased

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name 2 diseases with mitochondrial inheritance

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Leber's hereditary optic neuropathy; mitochondrial myopathies

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what is heteroplasmy?

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presence of normal as well as mutated mitochondrial DNA

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what is nondisjunction?

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failure of separation of chromosomes

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what is a balanced translocation?

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occurs when non-homologous chromosomes exchange genetic material in such a way that no critical genetic material is lost

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what is an unbalanced translocation?

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occurs when non-homologous chromosomes exchange genetic material with a net loss or gain of critical genetic material

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what is an inversion?

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chromosomal rearrangement in which the central segment produced by two breaks is inverted prior to repair of the breaks

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inversions that include the centromere are called what?

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pericentric

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what do you call inversions that don't include the centromere?

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paracentric

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what is the outcome of a crossoer event within a paracentric inversion?

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formation of an acentric fragment and dicentric bridge - this cell will not complete meiosis

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an abnormality in what can produce tirpolar mitoses?

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mitotic spindle

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what is synapsis?

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pairing of homologous chromosomes with which meiosis begins

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the incidence of an X-linked recessive disease in the male portion of a population is a direct estimate of what?

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the gene frequency in the population

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what is confined placental mosaicism?

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consequence of a genetic aberration occuring in the trophoblast or in extraembryonic progenitor cells in the ICM - the genetic abnormality leads to abnormal placental development and intrauterine growth retardation

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what is the only topoisomerase that can introduce negative supercoils into DNA?

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DNA gyrase - used to stabilize underwound helices

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what do hammerhead ribozymes do?

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catalyze sequence-specific cleavage of RNA phosphodiester bonds due to the secondary structure they form