Genetics Vocab Ch. 5 Of Pierce 3Rd Ed

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anticipation

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increasing severity or earlier age of onset of a genetic trait in succeeding generations. For example, symptoms of a genetic disease may become more severe as the trait is passed from generation to generation

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codominance

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type of allelic interaction in which the heterozygote simultaneously expresses traits of both homozygotes

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complementation

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two different mutations in the heterzygous condition are exhibited as the wild-type phenotype; indicates that the mutations are at different loci

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complementation test

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test designed to determine wheter two different mutations are at the same locus (are allelic) or at different loci (are nonallelic). Two individuals that are homozygous for two independently derived mutations are crossed, producing F1 progeny that are heterozygous for the mutations. If the mutations are at the same locus, the F1 will have a mutant phenotype. If the mutations are at different loci, the F1 will have a wild-type phenotype.

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continuous characteristic

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displays a large number of possible phenotypes that are not easily distinguished , such as human height

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cytoplasmic inheritance

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inheritance of characteristics encoded by genes located in the cytoplasm. Because the cytoplasm is usually contributed entirely by only one parent, most cytoplasmically inherited characteristics are inherited from a single parent.

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discontinuous characteristic

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exhibits only a few easily distinguished phenotypes. An example is seed shape in which seeds are either round or wrinkled

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epigenetics

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phenonmena due to alterations to DNA that do not include changes in the base sequence; often affect the way in which the DNA sequences are expressed. Such alterations are often stable and heritable in the sense that they are passed from one cell to another

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epistasis

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type of gene interaction in which a gene at one locus masks or suppresses the effects of a gene at different locus

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epistatic gene

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masks or suppresses the effect of a gene at a different locus

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expressivity

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degree to which a trait is expressed

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gene interaction

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interactions between genes at different loci that affect the same characteristic

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genetic maternal effect

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determines the phenotype of an offspring. With genetic maternal effect, an offspring inherits genes for the characteristics from both parents, but the offspring's phenotype is determined not by its own genotype but by the nuclear genotype of its mother

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genomic imprinting

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differential expression of a gene that depends on the sex of the parent that transmitted the gene. If the gene is inherited from the father, its expression is defferent from that if it is inherited from the mother

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hypostatic gene

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gene that is masked or suppressed by the action of a gene at a different locus

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incomplete penetrance

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refers to a genotype that does not always express the expected phenotype. Some individuals possess the genotype for a trait but do not express the phenotype

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lethal allele

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causes the death of an individual organism, often early in development, and so the organism does no appear in the progeny of a genetic cross. Recessive lethal alleles kill individual organisms that are homozygous for the allele; domminant lethals kill both heterozygotes and homozygotes.

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multifactrial characteristic

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determined by multiple genes and environmental factors

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multiple alleles

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presence in a group of individuals of more that two alleles at a locus. Although, for the group, the locus has more than two alleles, each member of the group has only two of the possible alleles.

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norm of reaction

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range of phenotypes produced by a particular genotype in different environmental conditions

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penetrance

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percentage of individuals with a particular genotype that expresses the phenotype expected of that genotype

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phenocopy

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phenotype that is produced by environmental effects and is the same as the phenotype produced by a genotype

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pleiotropy

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a single genotype influences multiple phenotypes

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polygenic characteristic

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encoded by genes at many loci

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quantitative characteristic

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continuous characteristic; desplays a large number of possible phenotypes, which must be described by a quantitative measurement

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sex-influenced characteristic

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encoded by autosomal genes that are more readily expressed in one sex. For example, an autosomal dominant gene may have higher penetrance in males than in females or an autosomal gene may be dominant in males but recessive in females

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sex-limited characteristic

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encoded by autosomal genes and expressed in only one sex. Both males and females carry genes for sex-limited characteristics, but the characteristics appear in only one of the sexes

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temperature-sensitive allele

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expressed only at certain temperatures