Acrocentric chromosome:
A chromosome with the centromere near one end such that it has one long arm plus a stalk and a satellite.
Activators:
The major class of transcription regulatory proteins in eukaryotes. Binding of these proteins to regulatory DNA sequences associated with specific genes determines the efficiency of transcription initiation. Some bacterial genes are controlled by activators.
Adenine (A):
A purine base found in DNA and RNA. In double stranded DNA, adenine pairs with thymine, a pyrimidine, by hydrogen bonding. In double-stranded RNA, adenine pairs with uracil, a pyrimidine, by hydrogen bonding.
Agarose gel electrophoresis:
An experimental procedure in which an electric field is used to move DNA or RNA molecules, which are negatively charged, through a gel matrix of agarose from the negative pole to the positive pole.
Allele:
One of two or more alternative forms of a single gene that can exist at the same locus in the genome. All the alle les of a gene determine the same hereditary trait (e.g., seed colour), but each has a unique nucleotide sequence, which may result in different phenotypes (e.g., yellow or green seeds).
Allele frequency:
Proportion of a particular allele at a locus within a gene pool. The sum of the allele frequencies at a given locus is 1.
Allele-specific oligonucleotide (ASO) hybridization: A procedure, using PCR primers, to distinguish alleles that differ by one base pair.
Allelomorph:
One of two or more alternative forms of a single gene that can exist at the same locus in the genome.
Allopolyploidy:
Condition in which a cell or organism has two or more genetically distinct sets of chromosomes that originate in different, though usually related, species.
Alternation of generations:
Type of life cycle characteristic of green plants in which haploid cells (gametophytes) alternate with diploid cells (sporophytes).
Alternative polyadenylation:
Process for generating different functional mRNAs from a single gene by cleavage and polyadenylation of the primary transcript at different poly(A) sites.
Alternative splicing:
In eukaryotes, a process for generating different functional mRNAs from a single precursor mRNA (pre-mRNA) by incorporating different exons in the mature mRNA.
Ames test:
An assay that measures the ability of chemicals to cause mutations in certain bacteria. It can identify potential carcinogens.
Amino acid:
Any of the small molecules, containing a carboxyl group and amino group, that are joined together to form polypeptides and proteins.
Aminoacyl–tRNA:
A tRNA molecule covalently bound to an amino acid; also called charged tRNA. This complex brings the amino acid to the ribosome so that it can be used in polypeptide synthesis.
Aminoacyl–tRNA synthetase:
An enzyme that catalyzes the addition of a specific amino acid to the tRNA for that amino acid.
Amniocentesis:
A procedure in which a sample of amniotic sac fluid is withdrawn from the amniotic sac of a developing fetus and cells are cultured and examined for chromosomal abnormalities.
Analysis of variance (ANOVA):
A series of statistical procedures for determining whether differences in the means of a variable in two samples are significant and for partitioning the variance into components.
Anaphase:
The stage in mitosis when the sister chromatids separate and migrate toward the opposite poles of the cell.
Anaphase I:
The stage in meiosis I when the chromosomes in each bivalent separate and begin moving toward opposite poles of the cell.
Anaphase II:
The stage in meiosis II when the sister chromatids are pulled to the opposite poles of the cell.
Aneuploid:
Referring to an organism or cell that has a chromo some number that is not an exact multiple of the haploid set of chromosomes.
Aneuploidy:
Any condition in which the number of chromosomes differs from an exact multiple of the normal haploid number in a cell or organism. It commonly results from the gain or loss of individual chromosomes but also can result from the duplication or deletion of part(s) of a chromo some or chromosomes.
Antibody:
A protein molecule that recognizes and binds to a foreign substance introduced into the organism.
Anticodon:
A group of three adjacent nucleotides in a tRNA molecule that pairs with a codon in mRNA by complementary base pairing.
Antigen:
Any large molecule that stimulates the production of specific antibodies or binds specifically to an antibody.
Antiparallel:
In the case of double-stranded DNA, referring to the opposite orientations of the strands, with the 5′ end of one strand paired with the 3′ end of the other strand.
Antisense mRNA:
An mRNA transcribed from a cloned gene that is complementary to the mRNA produced by the nor mal gene.
Apoptosis:
Controlled process leading to cell death that is triggered by intracellular damage (e.g., DNA lesions) or by external signals from neighbouring cells. Also called programmed cell death.
Aporepressor protein:
An inactive repressor that is activated when bound to an effector molecule.
Applied research:
Research done with the objective of developing products or processes that can be commercialized or at least made available to humankind for practical benefit.
Archaea Prokaryotes:
Organisms that constitute one of the three main evolutionary domains of organisms. Members of this domain are called archaeans.
Artificial selection:
Process for deliberating changing the phenotypic traits of a population by determining which individuals will survive and reproduce.
Attenuation:
A regulatory mechanism in certain bacterial biosynthetic operons that controls gene expression by causing RNA polymerase to terminate transcription.
Autonomously replicating sequence (ARS):
A specific sequence in yeast chromosomes that, when included as part of an extrachromosomal, circular DNA molecule, confers on that molecule the ability to replicate autonomously; one type of eukaryotic replicator.
Autopolyploidy:
Condition in which a cell or organism has two or more genetically distinct sets of chromosomes of the same species.
Autosome:
A chromosome other than a sex chromosome.
Auxotroph:
A mutant strain of an organism that cannot synthesize a molecule required for growth and therefore must have the molecule supplied in the growth medium for it to grow. Also called auxotrophic mutant or nutritional mutant.
Auxotrophic mutant:
A mutant strain of an organism that cannot synthesize a molecule required for growth and therefore must have the molecule supplied in the growth medium for it to grow. Also called auxotrophic mutant or nutritional mutant.
Auxotrophic mutation:
A mutation that affects an organism’s ability to make a particular molecule essential for growth. Also called nutritional mutation.
