Biology Reference
In-Depth Information
Intron:
Noncoding DNA that separates neighboring exons in a gene.
Linkage disequilibrium:
Nonrandom association of alleles at linked loci.
Locus:
The position of a gene or genetic marker on a chromosome.
Lod score:
A measure of the likelihood of genetic linkage between loci. A score
greater than +3 is often taken as evidence of linkage; one that is less than -2 is
often taken as evidence against linkage.
Megakaryocytes:
White blood cells that produce platelets by cytoplasmic budding.
Missense mutation:
A nucleotide substitution that results in an amino acid
change.
Multimeric complex:
Structure composed of several identical or different subunits
held together by weak bonds.
Nullisomy:
A diploid cell missing both copies of the same chromosome.
Oligonucleotide:
A short DNA molecule synthesized for use as a probe.
Open Reading Frame (ORF):
A significantly long sequence of DNA in which
there are no termination codons.
Penetrance:
The probability that a given genotype will result in a particular
phenotype.
Phenocopy:
A phenotype that looks the same as one produced by a specific geno-
type, but has a different etiology.
Pleiotropy:
Multiple phenotypic effects of a single gene.
Polycistronic mRNA:
Includes coding regions representing more than one
gene.
Polymorphism:
The occurrence together in a population of two or more alleles at
a locus, none of which are at a frequency that could be maintained by recurrent
mutation alone.
Polyploid:
Having multiple chromosome sets.
Positional cloning:
Cloning of a gene which is dependent only on knowledge of
its subchromosomal location.
Purine:
A nitrogen-containing compound with a double-ring structure (e.g.,
adenine and guanine).
Pyrimidine:
A nitrogen-containing compound with a single-ring structure (e.g.,
cytosine, thymine, and uracil).
Radiation hybrid:
A type of somatic cell hybrid in which fragments of chromo-
somes of one cell type are generated by exposure to X-rays, and are subsequently
allowed to integrate into the chromosomes of a second cell type.
Reproductive fitness:
Relative reproductive success of a genotype as measured by
survival, fecundity or other life history parameters.
Splice site:
The boundary between an intron and exon. The introns are removed
in the generation of mature mRNA.
Stop codon:
One of the three codons (UAG, UAA and UGA) that terminate syn-
thesis of a polypeptide.
Synteny:
The property of occurring on the same chromosome.
Transcription:
The assembly of a complementary single-stranded molecule of
RNA on a DNA template.
Transfection:
Transfer of a gene, or cDNA (next to a promoter), into a cell,
enabling the transfected cell to form a new gene product.
Transition:
A nucleotide substitution in which one purine is replaced by another,
or one pyrimidine is replaced by another.
