bacterial genetics : the study of mechanisms of heredity in bacteria.
biochemical genetics : the science concerned with the chemical and
physical nature of genes and the mechanism by which they control the development
and maintenance of the organism.
mathematical genetics : the statistical analysis of probabilities
of genetic transmission, genes in populations, and hypothesis testing.
molecular genetics : that branch of genetics concerned with the
molecular structure and activities of the genetic material, including the
replication of DNA, its transcription into RNA, and the translation of
RNA to form proteins.
gene : a segment of a DNA molecule that contains
all the information required for synthesis of a product (polypeptide chain
or RNA molecule), including both coding and noncoding sequences. It is
the biologic unit of heredity, self-reproducing, and transmitted from parent
to progeny. Each gene has a specific position (locus) on the chromosome
allelic genes / alleles : any alternative
form of a gene that can occupy a particular chromosomal locus. In humans
and other diploid organisms there are two alleles, one on each chromosome
of a homologous pair
multiple alleles : a series of > 2 alleles.
Mendel's laws : the laws of inheritance
of single-gene traits that form the basis of the science of genetics, first
described by Gregor Mendel in 1865. From experimental crosses of pea plants
differing in one or more characteristics determined by single genes, and
counting the types of progeny in successive generations, Mendel derived
2 laws now usually expressed as
the law of segregation (the members of a pair of allelic genes segregate
from one another and pass to different gametes)
the law of independent assortment (genes that are not alleles are distributed
to the gametes independently of one another).
autosomal gene : a gene located on any chromosome that is not a
sex-conditioned or -influenced gene : a gene that is fully expressed
in one sex only, e.g. human baldness.
sex-limited gene : a sex-linked or autosomal gene that will produce
an effect in one sex only.
sex-linked gene : a gene carried on a sex chromosome (X or Y); only
X linkage has clinical significance, and sex linkage is more correctly
called X linkage.
X-linked gene : a gene carried on the X chromosome; the corresponding
trait, whether dominant or recessive, is always expressed in males, who
have only one X chromosome. X linkage is used sometimes synonymously with
sex linkage since no genetic disorders have as yet been associated with
genes on the Y chromosome.
Y-linked gene : a gene located on the Y chromosome; the trait determined
by it is therefore exhibited only by males and is transmitted by a father
to all of his sons. Other than the genes that determine maleness, no clinically
significant Y-linked genes have been identified in human beings.
holandric genes : genes in the nonhomologous region of the Y chromosome.
chimeric gene : an artificial gene constructed by juxtaposition
of fragments of unrelated genes or other DNA, which may themselves have
been altered in sequence.
penetrance : the frequency of expression of a genotype. If it is
< 100%, the trait is said to exhibit reduced penetrance or lack
of penetrance. In an individual who has a genotype that characteristically
produces an abnormal phenotype but is phenotypically normal, the trait
is said to be nonpenetrant.
dominant gene : one that is phenotypically expressed when present
either in homozygous or heterozygous form
recessive gene : one that is phenotypically expressed only when
homozygous or hemizygous
codominant genes / codominance : alleles that are both fully expressed
in the heterozygote
complementary or reciprocal genes : 2 independent pairs of nonallelic
genes, neither of which will produce its effect in the absence of the other
gene complex : a DNA segment containing a number of genes coding
for products with related functions, e.g. the human major histocompatibility
cumulative genes / polygenes : one of a group of nonallelic genes
(multiple factors or cumulative genes) that interact to influence the same
character in the same way so that the effect is cumulative
histocompatibility (H) gene : a gene that determines a histocompatibility
housekeeping gene : a gene that theoretically must be expressed
in all cells because it encodes proteins needed for basic functioning.
immune response (Ir) genes : genes that govern the immune response
to certain antigens. Animals carrying the gene are responders; those lacking
the gene are nonresponders. In all species studied they are autosomal dominant
genes that map with the genes for class II MHC antigens; thus the HLA-D/DR
genes are probably immune response genes in humans.
immune suppressor (Is) genes : genes governing the ability of suppressor
T cells to respond to certain antigens.
immunoglobulin genes : the genes coding for immunoglobulin heavy
and light chains, which are organized in three loci coding for k light
chains, l light chains, and heavy chains found on human chromosomes 2,
22, and 14, respectively. These genes undergo several DNA rearrangements
during the differentiation of stem cells into B cells and plasma cells,
permitting synthesis of the various immunoglobulin classes.
cell interaction (CI) genes : genes of the major histocompatibility
complex that control cell-cell interactions between B cells, T cells, and
macrophages and between cytotoxic T cells and target cells.
lethal gene : a gene the presence of which brings about the death
of the organism, or permits its survival only under certain conditions;
see also lethal equivalent.
sublethal gene : a gene the presence of which handicaps or impairs
the function of the organism.
major gene : a gene whose effect on the phenotype is always evident,
regardless of how this effect is modified by other genes.
mutant gene : a gene in which the loss, gain, or exchange of material
has resulted in a permanent transmissible change in function. Such a gene
may have become practically inactive (amorph), may act to antagonize
or inhibit normal activity (antimorph), may act to increase normal
activity (hypermorph), or may show only a slight reduction in its effectiveness
(leaky gene or hypomorph)
silent gene or allele : a mutant gene having no detectable phenotypic
leaky gene : one in which a switch in the sequence of bases in a
nucleotide results in the production of a mutant protein that, because
of a single amino acid replacement, has only partial enzymatic activity;
wild-type gene : the normal allele of a gene, sometimes symbolized
wild type : in genetics, the standard phenotype for any experimental
organism; also a gene that determines a standard phenotypic trait
pleiotropic gene : one producing many effects in the phenotype.
repressed gene : one that under normal conditions does not always
function to produce the maximum number of enzymes
derepressed gene : one that in response to an environmental demand
for a particular enzyme functions to increase production of that enzyme
split gene : a gene containing multiple exons and at least one intron.
supplementary genes : 2 independent pairs of genes that interact
in such a way that one dominant will produce its effect even in the absence
of the other, but the second requires the presence of the first to be effective.
syntenic genes : genes located on the same chromosome.
tumor suppressor gene / antioncogene : a gene whose function is
to limit cell proliferation and loss of whose function leads to cell transformation
and tumor growth
From the standpoint of function, genes are conceived of as :
structural gene : a gene that specifies the amino acid sequence
of a polypeptide chain. Messenger RNA is its primary product.
operator gene or locus : in bacterial genetics, a gene that serves
as a starting point for reading the genetic code and controls the activity
of the structured genes by interacting with a repressor
regulator, regulatory or repressor gene : in genetic theory, a gene
that synthesizes repressor, a substance which, through interaction with
the operator gene, switches off the activity of the structural genes associated
with it in the operon. More generally, a gene whose product affects the
activity of other genes.
haplotype : the combination of alleles or genetic markers that is
found on a single chromosome of a given individual.
law : each parent contributes, on an average, one half, or (0.5), of
an individual's heritage, each grandparent one fourth, or (0.5)2,
each greatgrandparent one eighth, or (0.5)3, etc.
law of regression
: average parents tend to produce average children, but the offspring of
extreme parents inherit the parental peculiarities in a less marked degree
than the latter were manifested in the parents themselves
complementation : the interaction
between 2 sets of cellular or viral genes introduced into the same cell,
such that the cell can function even though each set of genes carries a
mutated, nonfunctional gene; it indicates that the defects are not identical.
intercistronic or intergenic complementation : the essentially full
restoration of wild-type function in a cis-trans test when two mutations
are located in two different cistrons (genes)
intracistronic, interallelic or intragenic complementation : the
partial restoration of function sometimes seen in the cis-trans test when
the two mutations are located at different sites within the same cistron.
eugenics / orthogenics : the improvement
of a population by selection of its best specimens for breeding
negative eugenics : that concerned
with prevention of reproduction (procreation) by individuals possessing
inferior or undesirable traits.
positive eugenics : that concerned
with promotion of optimal reproduction of individuals possessing superior
or desirable traits.
dysgenics : the study of racial deterioration
backcross : in experimental genetics, a mating between a heterozygote
and a homozygote.
double backcross : the mating between a double heterozygote and
Virtual Genetics Lab (VGL)
software for Macs®, Linux, UNIX®, and Windows. Created by a team
of graduate students at the UMASS Boston, VGL allows students to perform
in silico crossings of imaginary flies and, by observing the characteristics
of the progeny, predict the genetic makeup of the parents, show how theoretical
phenotypes are being passed on, and determine complex traits, such as incomplete
dominance and others.