Ch. 5 Extensions and Modifications of Basic Principles Flashcards
complete dominance
type of dominance in which the same phenotype is expressed in homozygous (AA) and in heterozygotes (Aa); only the dominant allele is expressed in a heterozygote
incomplete dominance
type of dominance in which the phenotype of the heterozygote is intermediate between the phenotypes of the two homozygotes
codominance
type of allelic interaction in which the heterozygote simultaneously expresses traits of both homozygotes
incomplete penetrance
a case in which some individuals possess the genotype for a trait but do not express the expected phenotype
penetrance
percentage of individuals with a particular genotype that express the phenotype expected of that genotype
expressivity
degree to which a trait is expressed
lethal allele
allele that causes the death of an individual organism, often early in development, so that the organism does not appear in the progeny of a genetic cross. a recessive lethal allele kills individuals that are homozygous for the allele; a dominant lethal allele kills both heterozygotes and homozygotes
multiple alleles
presence of more than two alleles at a locus in a group of diploid individuals; however, each individual member of the group has only two of the possible alleles
compound heterozygote
an individual with two different recessive alleles at a locus that results in a recessive phenotype
gene interaction
interaction between genes at different loci that affect the same characteristic
epistasis
type of gene interaction in which a gene at one locus masks or suppresses the effects of a gene at a different locus
epistatic gene
gene that masks or suppresses the effect of a gene at a different locus
hypostatic gene
gene that is masked or suppressed by the action of a gene at a different locus
complementation test
test designed to determine whether 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
complementation
manifestation of two different mutations in the heterozygous condition as the wild-type phenotype; indicates that the mutations are at different loci
sex-influenced characteristic
characteristic 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
sex-limited characteristic
characteristic 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
cytoplasmic inheritance
inheritance of characteristics encoded by genes located in the cytoplasm. because the cytoplasm is usually contributed entirely by one parent, most cytoplasmically inherited characteristics are inherited from only one parent
genetic maternal effect
determination of the phenotype of an offspring not by its own genotype, but by the nuclear genotype of its mother
genomic imprinting
differential expression of a gene that depends on the sex of the parent that transmitted the gene
epigenetics
phenomena due to alterations in DNA that do not include changes in the base sequence; often affect the way in which DNA sequences are expressed. such alterations are often stable and heritable in the sense that they are passed to descendant cells or individuals
anticipation
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
temperature-sensitive allele
allele that is expressed only at certain temperatures
phenocopy
phenotype produced by environmental effects that is the same as the phenotype produced by a genotype
discontinuous characteristic
characteristic that exhibits only a few, easily distinguished phenotypes. an example is seed shape in which seeds are either round or wrinkled
continuous characteristic
characteristic that displays a large number of possible phenotypes that are not easily distinguished, such as human height
quantitative characteristic
continuous characteristic; displays a large number of possible phenotypes or is encoded by multiple genetic factors
polygenic characteristic
characteristic encoded by genes at many loci
pleiotropy
ability of a single gene to influence multiple phenotypes
multifactorial characteristic
characteristic determined by multiple genes and environmental factors
