Chapter 4 Flashcards
pleiotropy
A condition in which a single mutation causes multiple phenotypic effects.
the phenomenon in which a single locus affects two or more distinct phenotypic traits.
gene interaction
The production of novel phenotypes by the interaction of alleles of different genes.
X-linkage
The pattern of inheritance resulting from genes located on the X chromosome.
allele
One of the possible alternative forms of a gene, often distinguished from other alleles by phenotypic effects.
loss-of-function mutation
A mutation that produces alleles encoding proteins with reduced or no function.
null allele
A mutant allele that produces no functional gene product. Usually inherited as a recessive trait.
gain-of-function mutations
A type of mutation in which the gene product takes on a new function and produces a phenotype different from that of the normal allele and from any loss-of-function alleles.
neutral mutations
A mutation with no perceived immediate adaptive significance or phenotypic effect.
incomplete, dominance
Expressing a heterozygous phenotype that is distinct from the phenotype of either homozygous parent. Also called partial dominance.
partial, dominance
Expressing a heterozygous phenotype that is distinct from the phenotype of either homozygous parent. Also called incomplete dominance.
codominance
A condition in which the phenotypic effects of a gene’s alleles are fully and simultaneously expressed in the heterozygote.
H substance
The carbohydrate group present on the surface of red blood cells to which the A and/or B antigen may be added. When unmodified, it results in blood type O.
Bombay phenotype
A rare variant of the ABO antigen system in which affected individuals do not have A or B antigens and thus appear to have blood type O, even though their genotype may carry unexpressed alleles for the A and/or B antigens.
dominant lethal allele
a gene variant that causes death when present in a single copy of an organism
gene interaction
The production of novel phenotypes by the interaction of alleles of different genes.
epigenesis
The idea that an organism or organ arises through the sequential appearance and development of new structures which holds that development is the result of the assembly of structures already present in the egg.
heterogeneous trait
A mutant phenotype that may occur as the result of a mutation in any one of many genes required for normal expression of the trait during development, e.g., hereditary deafness.
complementation group
A test that determines if two mutations are in the same gene or different genes
a genetic interaction that occurs when two mutations affect the same phenotype but are located in different genes
X-linkage
The pattern of inheritance resulting from genes located on the X chromosome.
hemizygous
Having a gene present in a single dose in an otherwise diploid cell. Usually applied to genes on the X chromosome in heterogametic males.
chromosome theory of inheritance
states that genes are located on chromosomes, and the behavior of chromosomes during meiosis explains the patterns of inheritance observed by Mendel
sex-limited inheritance
A trait that is expressed in only one sex even though the trait may not be X-linked or Y-linked.
sex-influenced inheritance
A phenotypic expression conditioned by the sex of the individual. A heterozygote may express one phenotype in one sex and an alternate phenotype in the other sex (e.g., pattern baldness in humans).
penetrance
The frequency, expressed as a percentage, with which individuals of a given genotype manifest at least some degree of a specific mutant phenotype associated with a trait.
expressivity
The degree to which a phenotype for a given trait is expressed.
position effect
A change in expression of a gene associated with a change in the gene’s location within the genome.
temperature-sensitive mutations
A conditional mutation that produces a mutant phenotype at one temperature and a wild-type phenotype at another.
conditional mutations
A mutation expressed only under a certain condition; that is, a wild-type phenotype is expressed under certain (permissive) conditions and a mutant phenotype under other (restrictive) conditions.
