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Pathophysiology of Disease - Ch. 2


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What do the pathophysiologic principles that distinguish disease focus on?
They focus on the mechanisms of mutation, inheritance, and molecular pathways from genotype to phenotype
Terminal location of the centromere on chromosomes 13, 14, 15, 21, and 22, which contain so-called satellite DNA on their short arms that encodes for ribosomal RNA genes
Allelic heterogeneity
The situation in which multiple alleles at a single locus can produce on or more disease phenotypes
Refers to mutations that when present in heterozygous form opposite a nonmutant allele will result in a phenotype similar to homozygosity for loss of function alleles.
Ascertainment bias
The situation in which individuals or families in a genetic study are not representative of the general population because of the way in which they are identified.
Located on chromosomes 1-22 rather than X or Y
CpG island
A segment of DNA that contains a releatively high density of 5' -GC- 3' dinucleotides. Such segments are frequently unmethylated and located close to ubiquitously expressed genes.
The of of prophase during female meiosis I in which fetal oocytes are arrested prior to ovulation.
A pattern of inheritance of mechanism of gene action in which the effects of a variant allele can be observed in the presence of a nonmutant allele.
Dominant negative
A type of pathophysiolic mechanism that occurs when a mutant allele interferes with the normal function of the nonmutant gene product.
Dosage compensation
Mechanism by which a difference in gene dosage between 2 cells is equalized. For XX cells, decreased expression from one of the 2 X chromosomes results in a concentration of gene product similar to an XY cell.
End product deficiency
A pathological mechanism in which absence or reduction in the product of a particular enzymatic reaction leads to disease.
Refers to a phenotypic effect that does nto depend on genotype. DNA methylation that occurs during gametogenesis can affect gene expression in zygotic cells, but the pattern of methylation can also be reversed in subsequent generations and thus does not affect the genotype
The extent to which a mutant gentoype affects the phenotype; a quantitative measure of a disease state that may vary from mild to severe but is never completely absent.
The likelihood tha an individual who carries a particular mutant allele will produce progeny tha talso carry the allele
Founder effect
One of several possible explanations for an unexpectedly high frequency of deleterious gene in a population. If the population was founded by a small ancestral group, it may have, by chance, contained a large number of carriers for deleterious gene
The egg or sperm cell that represents a potential reproductive contribution to the next generation. Gametes have undergone meiosis and so contain half the normal number of chromosomes found in zygotic cells
Gene Dosage
The principle that the amount of product expressed for particualr gene is proportionate to the number of gene copies present in a cell
Genetic anticipation
A clinical phenomenom in which a phenotype observed in individuals carrying a deleterious gene appears more severe in successive generations. Possible explanations include ascertainment bias or a multipstep muational mechanism such as expansion of triplet repeats
A set of cloesely lined alleles that are not easily separated by recombination; often refers to DNA sequence alterations such as restriction fragment length polymorphisms
A term referring to the presence of only one allele at a locus, either because the other allele is deleted or because it is normally not present, eg, X-linded genes in males
One of the two alternaitve forms of chromasomal material (the other is euchromatin) in which chromosamal DNA is bound to proteins and condensed. Heterochromatin is highly condensed and usually does not contain gnes that are activly transcribed
The mixture of mutant and nonmutant mtDNA molecules in a single cell.
Heterozygote advantage
One way to explain an unexpectedly high frequency of recessively inherited mutation in a particular population. During recent evolution, carriers (ie, heterozygotes) are postulated to have had a higher fitness than homozygous nonmutant indidividuals
Having two alleles a tthe same locus that are different.
Having two alleles at the same locus that are the same
Refers to a mutation tha has an effect similar to increasing the number of normal gene copies per cell
Refers to a mutation that reduces but does not eliminate th activity of a particular gene product
Most commonly, the process wheeby expression of a gene depends on whether it is transmitted through a female or male gamete
Linkage disqeuilibrium
A condition in which cetain combinations of closely linked alleles are present in frequencies no predicted by their individual frequency
Locus heterogeneity
A situation in which mutations of different genes produce similar or identical phenotypes. Also referred to as genetic heterogeneity
A form of inheritance tha obeys Mendel's law, ie, autosomal dominant, autosomal recessvie, X-linked dominanc or X-linked recessive.
A situation in which a genetic alteration is present in some but not all the cells of a single individual. In germline or gonadal mosaicism, the alteraion is present in germ cells but not somatic cells. In somatic mosaicism, the genetic alteraion is present in some but not all of the somatic cells ( and is gnerally not present in the germ cells)
A reduction in zygotic cells from two to one in the number of copies for a particular chromosomal segment or chromosome
Refers to a mutation that imparts a novel function to its gene product and consequently results in a phenotype distinct from an alteration in gene dosage.
Fialure ot two homologous chromosomes to separate, or disjoin at meaphase of meiosis II or mitosis
IN a single individual of a variant genotype, penetrance is qualitative all or non phenomemnom with respecgt to whether or not defined phenotypic criteria are present. In a population, reduced penetrance refers to the likelihood that an individual of a varieant genotype cannot be recogneezed accoriding to the same phenotypic criteria
Phenotypic heterogeneity
The situation that obtains when mutations of a single gene produce mutltiple different phenotypes
A mutational event that occurs after fertilization and that commly gives rise to mosaicism
A mutational event that occurs after fertilization and that commly gies rise to mosaicism

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