Allele One of a number of different forms of a gene. Each person inherits two alleles for each gene, one allele from each parent. These alleles may be the same or may be different from one another.
Recessive A gene that is phenotypically manifest in the homozygous state but is masked in the heterozygote by the presence of a dominant allele.
Dominant Refers to a characteristic that is apparent even when the relevant gene is present in only one copy. A dominant disorder can be inherited from only one parent.
Penetrance The probability of expressing a phenotype given a genotype. Penetrance is described as either"complete"or"incomplete."For example, individuals who carry the gene for tuberous sclerosis have an 80% chance of expressing the disorder. Penetrance may also be dependent on a susceptible individual's current age. For example, 20% of all gene carriers for myotonic dystrophy express the gene to some degree by age 15 while 80% of all gene carriers express it by age 60. ...
Epigenetic A factor that changes the phenotype without changing the genotype.
SNP Single necleotide polymorphism, or a single nucleotide position in the genomic sequence for which two or more alternative alleles are present at appreciable frequency (traditionally, at least 1%) in the human population.
Copy # The average number of molecules of a plasmid or gene per genome contained in a cell. (Loss or Gain)
Rearrangement A change in the usual order and arrangement of genetic material either within the chromosome complement or within a gene locus.
Translocation A rearrangement occurring when a piece of one chromosome is broken off and joined to another chromosome. An individual with a balanced translocation has the normal amount of chromosomal material. A person with an unbalanced translocation will have a loss or gain of chromosomal material.
Loss of Heterozygosity (LOH) A situation where one chromosome has a normal allele of a gene and one chromosome has a mutant or deleted allele.
Ploidy The number of (complete) sets of chromosomes in a cell or an organism. For example, haploid means one set and diploid means two sets.
Uniparental disomy When both members of a chromosome pair are contributed by one parent rather than one from each parent. Uniparental disomy may be maternal or paternal.
Tumor suppressor genes The role of tumor suppressor genes is to maintain the integrity of the DNA in cells. The activation of a tumor suppressor gene at certain "check points" puts on the "brakes" and allows the cell to check for any damage in its DNA. Usually repairs are made before the cell is allowed to go on and divide. Without these brakes, cells with damaged DNA would copy the damage and pass damage on to daughter cells. The damage becomes a permanent mutation in future generations of new cells. Tumor suppressor genes are recessive.
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