Glossary Picture

In the hope of helping the reader to understand certain genetic and other terms which may be unfamiliar, I have included this Glossary. It does not explain terms or concepts that have already been explained elsewhere in the brief, as for example, the concepts treated in the section headed "Lessons From Population Genetics." I have included here mostly terms which are technical enough to be omitted from most dictionaries. If the reader finds other unfamiliar words in the brief, their definitions will be found in any good collegiate dictionary.

achondroplasia - a genetic syndrome producing skeletal development resulting in a semi-dwarf phenotype with shortened and distorted limbs; occurring in some breeds (Alaskan Malamutes, e.g.) as a genetic defect, it is selected for as a breed point in others (Basset Hound, e.g.).

allele - an alternative form of a given gene producing a difference in the trait controlled by that gene; some genes have no alleles, some have two, some have multiple alleles for the same trait.

allozyme - enzymes differing in electrophoretic mobility (i.e., which migrate different distances through the substrate when an electrophoresis test is performed) as a result of allelic differences in a single gene; allozyme variation thus indicates genetic variation. One of the oldest lab tests for genetic analysis.

autochthonous - "sprung from the earth," native to a particular region from a very early time. The Siberian sleddog is an autochthonous dog in Siberia. (Pronounced "aw-TOC-thun-us.")

chromosomes - structures within the nuclei of living cells which are made up of nucleotide sequences, the biochemical information carriers which we call genes. All genes exist as tiny portions of chromosomes; although we may speak of particular genes individually, in isolation, they do not exist as separate entities, but are always found as subunits of chromosomes.

cynological - of or pertaining to the knowledge and study of dogs.

deleterious - harmful or injurious.

diploid - the body cells of most complex animal organisms such as birds and mammals all have their chromosomes in pairs derived from sexual reproduction, such that one chromosome of a pair comes from the father, the other from the mother. The sex cells from only one parent have only half the number of chromosomes of cells in other parts of the body; the normal chromosome number is known as the diploid number, the chromosome number of sperm and egg cells is called the haploid number.

disequilibrium - imbalance or instability.

dominant - said of an allele which by itself alone will produce a particular phenotype regardless of which other allele may be present on the other matching chromosome of the diploid pair; thus it takes only one copy of the chromosome to cause a dominant trait to be expressed in the phenotype.

electrophoresis - one of the most useful lab techniques for revealing genetic variation, which came into widespread use in the 1960s. It involves placing sample material (blood, e.g.) on a gel substrate. An electrical field is then applied between the two ends of the substrate, causing protein molecules to migrate through the gel. Proteins with different ionic charge will travel different distances across the substrate. Staining subsequently makes bands of protein in the substrate visible, so that various samples can be "read" in much the same manner as a supermarket bar coded label.

expression - not all genes possessed by an organism will result in detectable physical traits or differences in that organism; the genes that do are expressed. Dominant genes are always expressed, but recessive genes may be present for many generations without physical expression in the phenotype.

fecundity - the number of progeny produced by animals when reproducing.

fertility - the relative degree of reproductive success, i.e. the frequency with which mating is followed by pregnancy.

gametes - the sex cells of sexually reproducing organisms, i.e. spermatozoa and ova.

genome - the total genetic information possessed by an individual, a breed or a species.

genotype - the invisible genetic makeup of an individual organism, which includes alleles which may be recessive and therefore have no visible physical expression.

heterotypic - displaying different types. A breed which has more than one distinct and recognisable set of "type" characteristics is heterotypic.

heterozygote - an organism that possesses different alleles at a given gene locus.

heterozygous - possessing different alleles at a given gene locus.

holistic - relating to or focussing on the entirety of a thing or an organism and the interrelationship of its component parts, instead of emphasising different aspects or parts in isolation without considering their interactions.

homozygote - an organism that possesses identical alleles at a given gene locus.

homozygous - possessing identical alleles at a given gene locus.

inbreeding coefficient - a number used to quantify the probability that an organism will have identical alleles from the same ancestral source, usually computed by analysing the pedigree for "loops" in which the same ancestor is found on both the male and female sides of a mating.

lethal - likely to cause or capable of causing the death of an organism. A lethal gene is one which could either cause an aborted fetus or the death of the organism at some later stage of its life.

locus (pl. loci) - the physical location of a given gene on a particular chromosome.

meiosis - the kind of cell division which produces spermatozoa and ova or gametes and which reduces the chromosome number to half the normal complement.

microsatellite - a kind of DNA testing which detects short DNA sequence variations at particular highly variable sites; used in so-called "DNA fingerprinting."

phenotype - the visible physical expression of an individual organism's invisible genetic makeup.

polymorphism - difference or variation in form, diversity. Molecular geneticists study protein polymorphism, different forms of proteins in an organism indicating different alleles. Polymorphism studies show that from 20 to 50 percent of gene loci in most species have two or more allele forms.

recessive - a gene which contributes to the phenotype only if it is present in homozygous form. It takes two identical copies of a recessive gene to produce the trait it governs in the phenotype. In practice many genes are neither clearly dominant nor recessive, in which case geneticists speak of variable expressivity or incomplete penetrance.

RFLP - "restriction fragment length polymorphism" -- a DNA analysis technique which involves the use of enzymes to break the DNA chain at specific nucleotide sequences; the resulting "restriction fragments" are then analysed by the use of electrophoresis and blotting techniques. RFLPs are used as markers for known genetic traits and can be employed for genome mapping.

sublethal - having known deleterious effects which by themselves will not usually cause the death of the organism but which handicap it in some way. Several sublethal genes may nevertheless combine to form a "lethal equivalent."

subvital - having known effects which work to reduce the overall vitality and health of the organism.

typology - the study of types or groups of distinguishing characteristics. Typological thinking involves emphasis on visible superficial characteristics, often mere cosmetic traits which have little to do with the health and viability of the animal possessing them.

viability - the relative survivorship of the fertilised ova resulting from a reproductive event. Non-viability may involve ova which simply fail to develop, fetuses which abort, nestlings which die, or juveniles which fail to survive to maturity.

Next...
To this article's index page