Chapter 5 Flashcards
complete dominance
when the dominant allele completely covers up the recessive allele
incomplete dominance
refers to a genetic situation in which one allele does not completely dominate another allele, and therefore results in a new phenotype
(ex. A child with wavy hair as a result of one parent’s curly hair and the other’s straight hair)
- BLENDING
co-dominance
Relating to two alleles of a gene pair in a heterozygote that are both fully expressed (no blending, both expressed)
ex. black and white spots
incomplete penetrance
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.
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
Causes the death of an individual organism, often early in development, and so the organism does not appear in the progeny of a genetic cross. Recessive lethal alleles kill individual organisms that are homozygous for the allele; dominant lethals kill both heterozygotes and homozygotes
multiple alleles
Presence in a group of individuals of more than two alleles at a locus. However, each 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
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
Two different mutations in the heterozygous condition are exhibited 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 inherticance
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.
genetic maternal effect
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.
genomic imprinting
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 differs from that if the gene is inherited from the mother.
epigenetics
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.
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
Expressed only at certain temperatures.
phenocopy
Phenotype that is produced by environmental effects and is the same as the phenotype produced by a genotype.
discontinuous characteristic
Exhibits only a few, easily distinguished phenotypes. An example is seed shape in which seeds are either round or wrinkled.
continuous characteristic
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, which must be described by a quantitative measurement.
polygenic characteristic
Encoded by genes at many loci.
pleiotropy
A single genotype influences multiple phenotypes.
multifactoral characteristic
Determined by multiple genes and environmental factors.
