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Amniocentesis(am´-ne-o-sen-te´-sis) A technique of prenatal diagnosis in which amniotic fluid, obtained by aspiration from a needle inserted into the uterus, is analyzed to detect certain genetic and congenital defects in the fetus.
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CarrierIn genetics, an individual who is heterozygous at a given genetic locus, with one normal allele and one recessive allele. The heterozygote is phenotypically dominant for the character determined by the gene but can pass on the recessive allele to offspring.
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CharacterAn observable heritable feature.
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Chorionic villus sampling (CVS)(kor´-e-on´-ik vil´-us) A technique of prenatal diagnosis in which a small sample of the fetal portion of the placenta is removed and analyzed to detect certain genetic and congenital defects in the fetus
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CodominanceThe situation in which the phenotypes of both alleles are exhibited in the heterozygote because both alleles affect the phenotype in separate, distinguishable ways.
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Complete dominanceThe situation in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable.
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Cystic fibrosis(sis'-tik fi-bro'-sis) A human genetic disorder caused by a recessive allele for a chloride channel protein; characterized by an excessive secretion of mucus and consequent vulnerability to infection; fatal if untreated.
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Dihybrid(di´-hi´-brid) An organism that is heterozygous with respect to two genes of interest. All the offspring from a cross between parents doubly homozygous for different alleles are dihybrids. For example, parents of genotypes AABB and aabb produce a dihybrid of genotype AaBb.
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Dominant alleleAn allele that is fully expressed in the phenotype of a heterozygote.
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Epistasis(ep'-i-sta'-sis) A type of gene interaction in which one gene alters the phenotypic effects of another gene that is independently inherited.
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F1 generationThe first filial, or hybrid, offspring in a series of genetic crosses.
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F2 generationOffspring resulting from interbreeding of the hybrid F1 generation.
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Genotype(je´-no-tip) The genetic makeup, or set of alleles, of an organism.
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Heterozygous(het´-er-o-zi´-gus) Having two different alleles for a given gene.
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Homozygous(ho´-mo-zi´-gus) Having two identical alleles for a given gene.
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Huntington’s diseaseA human genetic disease caused by a dominant allele; characterized by uncontrollable body movements and degeneration of the nervous system; usually fatal 10 to 20 years after the onset of symptoms.
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HybridizationIn genetics, the mating, or crossing, of two true-breeding varieties.
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Incomplete dominanceThe situation in which the phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele.
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Law of independent assortmentMendel’s second law, stating that each pair of alleles segregates, or assorts, independently of each other pair during gamete formation; applies when genes for two characters are located on different pairs of homologous chromosomes.
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Law of segregationMendel’s first law, stating that the two alleles in a pair segregate (separate) into different gametes during gamete formation.
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MonohybridAn organism that is heterozygous with respect to a single gene of interest. All the offspring from a cross between parents homozygous for different alleles are monohybrids. For example, parents of genotypes AA and aa produce a monohybrid of genotype Aa.
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MultifactorialReferring to a phenotypic character that is influenced by multiple genes and environmental factors.
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Norm of reactionThe range of phenotypes produced by a single genotype, due to environmental influences.
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P generationThe parent individuals from which offspring are derived in studies of inheritance; P stands for “parental.”
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PedigreeA diagram of a family tree showing the occurrence of heritable characters in parents and offspring over multiple generations.
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Phenotype(fe´-no-tip) The physical and physiological traits of an organism, which are determined by its genetic makeup.
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Pleiotropy(pli-o´-truh-pe) The ability of a single gene to have multiple effects.
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Polygenic inheritance(pol´-e-jen´-ik) An additive effect of two or more genes on a single phenotypic character.
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Punnett squareA diagram used in the study of inheritance to show the predicted results of random fertilization in genetic crosses.
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Quantitative characterA heritable feature that varies continuously over a range rather than in an either-or fashion.
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