| G |
| guanine or guanosine. |
| g-banding |
| Technique for producing banding patterns
in eukaryotic chromosomes. Bands are produced by staining with Giemsa
stain after pretreating chromosomes with trypsin. Each homologous
chromosome pair has a unique pattern of g-bands, enabling recognition
of particular chromosomes. |
| gain-of-function dominant
|
| A mutation in which dominance is caused
by changing the specificity or expression pattern of a gene or gene
product, rather than simply by reducing or eliminating the normal
activity of that gene or gene product. |
| gamete |
| A germ cell having a haploid chromosome
complement. Gametes from parents of opposite sexes fuse to form
zygotes. A specialized haploid cell that fuses with a gamete from
the opposite sex or mating type to form a diploid zygote; in mammals,
an egg or a sperm. |
| gametic selection |
| The forces acting to cause differential
reproductive success of one allele over another in a heterozygote.
|
| gametophyte |
| The haploid stage of a plant life cycle
that produces gametes (by mitosis). It alternates with a diploid
sporophyte generation. The haploid gamete-producing stage in the
life cycle of plants; prominent and independent in some species
but reduced or parasitic in others. |
| gastrulation |
| The process of movements and infoldings
of embryonic cells destined to become endoderm in early animal embryos,
immediately following blastula (or blastoderm) stage, generating
the blastopore. |
| gene |
| segregating and heritable determinant of
the phenotype. The fundamental physical and functional unit of heredity,
which carries information from one generation to the next. A segment
of DNA, composed of a transcribed region and regulatory sequences
that make possible transcription. See also cistron; locus; Mendel's
first law. |
| gene amplification |
| A process by which the cell increases the
number of a particular gene within the genome. The process by which
the number of copies of a chromosomal segment is increased in a
cell. |
| gene cloning |
| The production of a lineage of cells all
of which contain one kind of DNA fragment of interest derived from
a population of many kinds of DNA fragments. Operationally by: |
| 1.inserting (recombining) a population of
DNA molecules, known to contain the DNA of interest, into a population
of vector DNA molecules in such a way that each vector molecule
contains only a single DNA molecule from the original population; |
| 2.transforming a population of host cells
with the vector DNA recombinants such that each host cell takes
up only one vector; |
| 3.growing single host cells separately (cloning)
by plating at low density to form a collection of separate colonies; |
| 4.screening the colonies (clones) formed
for the presence of the DNA of interest. |
| gene conversion |
| A meiotic process of directed change in
which one allele directs the conversion of a partner allele to its
own form. In asci of Ascomycete fungi a 4:4 ratio of alleles is
expected after meiosis, yet 6:2 and 5:3 ratios are sometimes observed.
A model of recombination, produced by Holliday, suggests that gene
conversion may be explained by repair of heteroduplex DNA. |
| gene dose |
| The number of copies of a particular gene
present in the genome. |
| gene family |
| A set of genes in one genome all descended
from the same ancestral gene. A group of genes that has arisen by
duplication of an ancestral gene. The genes in the family may or
may not have diverged from each other. |
| gene flow |
| The movement of genes from one population
to another by way of interbreeding of individuals in the two populations.
|
| gene fusion |
| The accidental joining of DNA of two genes,
such as can occur in a translocation or inversion. Gene fusions
can give rise to hybrid proteins or to the misregulation of the
transcription of one gene by the cis regulatory elements (enhancers)
of another. |
| gene interaction |
| The collaboration of several different genes
in the production of one phenotypic character (or related group
of characters). |
| gene locus |
| The specific place on a chromosome where
a gene is located. |
| gene map |
| 1. A linear designation of mutant sites
within a gene, based upon the various frequencies of interallelic
(intragenic) recombination. |
| 2. The DNA sequence of a gene annotated
with sites of regulatory elements, introns, exons and mutations.
|
| gene mutation |
| Mutation (point or larger change) that results
from changes within the structure of a gene. |
| gene pair |
| The two copies of a particular gene present
in a diploid cell (one in each chromosome set). |
| gene pool |
| All of the alleles available among the reproductive
members of a population from which gametes can be drawn. |
| gene therapy |
| The correction of a genetic deficiency in
a cell by the addition of new DNA and its insertion into the genome.
|
| generalized transduction
|
| The ability of certain phages to transduce
any gene in the bacterial chromosome. Form of transduction in which
any region of the host genome can be transduced. See specialized
transduction. |
| genetic code |
| linear sequences of three nucleotides (triplets)
that specify amino acids or termination (nonsense) codons during
the process of translation at the ribosome. The correspondence between
nucleotide triplets in DNA and amino acids in protein. |
| genetic dissection |
| The use of mutation and recombination to
piece together the various components of a given biological function.
|
| genetic engineering |
| Popular term for recombinant DNA technology.
|
| genetic fine structure
|
| The structure of the gene analyzed at the
level of the smallest units of recombination and mutation (nucleotides).
|
| genetic load |
| The relative decrease in the mean fitness
of a population due to the presence of genotypes that have less
than the highest fitness. |
| genetic map |
| A linear designation of sites within a chromosome
or genome, based upon the various frequencies of recombination between
genetic markers. See linkage map |
| genetic marker |
| allele, DNA marker or cytogenetic marker
used as experimental probe to keep track of an individual, a tissue,
a cell, a nucleus, a chromosome, or a gene. |
| genetic polymorphism
|
| The occurrence together in the same population
of more than one allele or genetic marker at the same locus with
the least frequent allele or marker occurring more frequently than
can be accounted for by mutation alone. |
| genetic variance |
| Phenotypic variance resulting from the presence
of different genotypes in the population. |
| genetics |
| (1) The study of genes through their variation.
(2) The study of inheritance. |
| genic balance theory
|
| The theory of Bridges that the sex of a
fruit fly is determined by the relative number of X chromosomes
and autosomal sets. |
| genome |
| The entire complement of genetic material
in a chromosome set. The entire genetic complement of a prokaryote,
virus, mitochondrion or chloroplast or the haploid nuclear genetic
complement of a eukaryotic species. |
| genomic library |
| A set of cloned fragments representing the
entire genome of an organism |
| genophore |
| The chromosome (genetic material) of prokaryotes
and viruses. |
| genotype |
| The specific allelic composition of a cell,
either of the entire cell or more commonly for a certain gene or
a set of genes. The genes that an organism possesses. |
| germ-line theory |
| A theory to account for the high degree
of antibody variability found in population. The germ-line theory
suggests that every B lymphocyte has all the genes for every type
of immunoglobulin but transcribes only one. See somatic mutation
theory. |
| germinal mutation |
| mutation occurring in cells that are destined
to develop into gametes. |
| Giemsa stain |
| A complex of stains specific for the phosphate
groups of DNA. |
| Gln |
| Glutamine (an amino acid). |
| Glu |
| Glutamate (an amino acid). |
| Gly |
| Glycine (an amino acid). |
| gradient |
| A gradual change in some quantitative property
over a specific distance. |
| gray crescent |
| A cortical region of the newly fertilised
egg of frogs and some salamanders that forms just after fertilization
on the side opposite sperm penetration. |
| ground state |
| The developmental state of a cell (or group
of cells) in the absence of activation of a developmental regulatory
switch. |
| group 1 intron |
| Self-splicing intron that requires an external
guanine-containing nucleotide for splicing; releases the intron
in a linear form. |
| group II intron |
| Self-splicing intron that does not require
an external nucleotide for splicing; releases the intron in a lariat
form. |
| group selection |
| Selection for traits that would be beneficial
to a population at the expense of the individual possessing the
trait. |
| guanine |
| A purine base that pairs with cytosine.
See purines. |
| guanosine |
| The nucleoside having guanine as its base.
|
| guide RNA (gRNA) |
| RNA that guides the insertion of uridines
(RNA editing) into mRNAs in trypanosomes. Found in transcripts from
minicircles and maxicircles of DNA in kinetoplasts. |
| gynandromorph |
| An individual that is a mosaic of male and
female structures. The underlying cause is frequently sex chromosome
mosaicism, such that some cells are chromosomal females while others
are chromosomal males. Mosaic individuals having simultaneous aspects
of both the male and the female phenotype. |
