Biology Reference
In-Depth Information
Centromere:
Primary constriction of a chromosome, separating the short arm
from the long arm. Its major function is to ensure correct segregation of homol-
ogous chromosomes during meiosis and mitosis.
Codon:
Nucleotide triplet that specifies an amino acid, or a signal for terminating
the synthesis of a polypeptide.
Consensus sequence:
In genes or proteins, an idealized sequence in which each
base or amino acid residue represents the one most frequently found at that posi-
tion when many actual sequences are compared.
Contig:
Continuous region of genomic DNA that has been cloned in a series of
identifiable overlapping DNA clones.
Degenerate code:
The genetic code is described as degenerate because more than
one codon can encode the same amino acid.
Dimerization:
The formation of a compound composed of two molecules.
Dominant negative mutation:
The abnormal product of one allele disrupts the
function of the product of the normal allele.
Endonuclease:
An enzyme that can cut phosphodiester bonds that occur inter-
nally in a DNA chain.
Epistasis:
Phenotypic expression is the result of interaction between alleles at
different loci.
EST (expressed sequence tag):
A sequence of part of the coding region of a gene.
Eukaryote:
Each cell has a nucleus that contains the genetic material, surrounded
by cytoplasm, which in turn is bounded by the plasma membrane that marks the
periphery of the cell.
Exon:
Segment of a gene that is decoded to give an mRNA product.
Frameshift Mutation:
A mutation in which there is a deletion or insertion of a
number of nucleotides that is not a multiple of three. This causes the codon
reading frame to shift.
Glutamic acid:
An amino acid that is part of the cochlear afferent cycle.
Haploid gametes:
Cells having only a single copy of each chromosome.
Haploinsufficiency:
A locus shows haploinsufficiency if producing a normal
phenotype requires more gene product than the amount produced by a single
copy.
Haplotype:
The particular combination of alleles in a defined region of a single
chromosome.
Hardy-Weinberg (equilibrium) law:
The relationship between gene frequencies
and genotype frequencies that is found in a population under certain conditions.
Heteromultimeric proteins:
Proteins that consist of nonidentical subunits (coded
by different genes).
Heteroplasmy:
Two or more genetically distinct populations of mitochondria in a
somatic cell tissue.
Heterozygous:
The individual's genotype at the locus consists of two different
alleles.
Histones:
Proteins associated with DNA in the chromosomes, rich in basic amino
acids (lysine or arginine) and virtually invariant throughout eukaryote evolution.
Homeodomain:
Conserved DNA binding domain consisting of the 60 amino acids
encoded by a homeobox gene.
Homozygous:
The individual's genotype at the locus consists of two identical
alleles.
