Glossary

This glossary is not, and is not intended to be, a dictionary of biological terms. The words and phrases here defined are only such as are used in the text of this book and such as may not be familiar to many readers. At the first use of a term in this text its meaning is explained. The glossary is intended for readers who have not perused the whole text or who have forgotten the definition of a term in their first encounter with it.

Acquired characters. Attributes developed in the body that are of environmental or functional origin, as opposed to those which have their cause in the germ plasma .

Albinism. The absence of any pigmentation.

Albino. An organism which does not have normal pigmentation.

In dogs, animals with bluish eyes, flesh colored nose, and white coat.

Alleles or Allelomorphs. Alternative forms of the same gene which influence the same developmental process or processes, but in different ways.

Amnion. The inner membrane in which the embryo of the higher animals develops.

Amniotic fluid. The liquid in which the developing embryo is bathed.

Artificial insemination. The artificial introduction of semen into the genitalia of the female without copulation.

Autosomes. Any chromosomes other than sex chromosomes.

Back-cross. The offspring of the cross of an F1 hybrid to either of the parental types.

Biology. The science which treats of life and living organisms.

Breed, n. A group of domestic animals controlled by man to prevent mixture with dissimilar groups and consequent loss of distinctive traits. In dogs, a breed is the largest group and is composed of more than one variety.

Caesarian section. The surgical delivery of young by section of the abdominal walls and uterus, used when normal birth is apparently impossible.

Castration. The surgical removal of the gonads, particularly of the testicles; not to be confused with other methods of sterilization.

Cell. The unit of protoplasmic structure in living organisms; a small mass of cytoplasm with its nucleus.

Centrosome or centriole. A small body within the cell which divides in mitosis or meiosis and around the divisions of which the split chromosomes group themselves.

Character. A distinguishing attribute or property of an organism. See also trait.

Chorion. The outer membrane which encloses the embryo.

Chromatin. A substance within the nucleus of the cell from which the chromosomes develop, so-called from its ability to take a stain.

Chromosomes. Dark-staining bodies which appear during cell division and which carry the heritable factors, the genes. They occur in pairs, one derived from the mother, the other from the father. Members of a pair carry the same allelic genes in identical arrangement.

Cleavage. The division of the fertilized ovum into many cells.

Clitoris. An erectile organ of the female at the anterior part of the vulva; the homologue of the penis.

Coitus. The act of copulation.

Complementary factors. Two or more dissimilar factors which unite to produce a trait.

Congenital. Present at birth, to be distinguished from hereditary.

Corpus cavernosum. Erectile tissue in the posterior part of the dog's penis which is grasped by the vaginal sphincter of the bitch to make possible the characteristic, prolonged coitus of the canine species.

Corpus luteum. (pi. corpora lutea) A yellowish mass formed in the ovary by the degeneration of the Graafian follicle after the discharge of the ovum and functioning as an endocrine gland.

Cowper's glands. Small glands in the male near the base of the bladder, not present in the dog.

Criss-cross inheritance. A mode of transmission in which characters of one parent are passed to progeny of the opposite sex.

Crossing over. The exchange of corresponding parts between the members of a pair of chromosomes during synapsis.

Cryptorchidism or Cryptorchism. A developmental defect in which the testicles remain in the abdominal cavity instead of descending into the scrotum.

Cytology. The science which treats of cells.

Dihybrids. The progeny from parents which differed in two Men-delian traits.

Diploid. The double number of chromosomes in all cells except the functional spermatozoa and ova.

Dominant. Said of one of a pair of alleles whose effects are expressed to the exclusion of the effects of the other allele. See also homozygous and heterozygous (q-v.).

Drag of the race. The tendency within purebred varieties, when artificial selection is not employed, to revert to the norm of the species.

Drosophila melanogaster. A species of fruit fly which, because of its rapidity of maturity and reproduction and because of the small number of its chromosomes, has lent itself to genetic experimentation.

Ductless gland. See endocrine glands.

Duplicate factors. Genes of different pairs which determine the same characters.

Embryo. The unborn organism, especially in the earlier stages of its development; the fetus .

Embryology. The science which treats of the prenatal development of the organism.

Endocrine glands. The ductless glands which produce hormones and discharge them directly into the blood stream. They include the pituitary, thyroid, thymus, parathyroid, adrenal, pineal, and other glands, besides the interstitial glands of the gonads.

Epididymis. An oblong body composed of the efferent duct of the testis, at the posterior part of that organ.

Fi. The first generation offspring of a given mating. The F2 (2nd generation) is produced by intercrossing the Fx.

Factor. The term originally used for what is now called gene.

Fallopian tubes. The passages by which the ova are conveyed from the ovaries to the uterus and in which conception normally occurs; oviducts.

Fetus . The unborn organism, especially in the later stages of its development; the embryo.

Fraternal twins. Two members of the same litter developed from different ova and spermatozoa but with the same parents, distinguished from identical twins (q.v.). Litter siblings.

Gene. The basic unit of heredity, believed to be the fundamental factor of inherited characteristics.

Genetics. The branch of biology which deals with heredity, variation, sex determination, and related phenomena.

Genotype. The hereditary makeup of an individual as distinguished from the expression or manifestation of the genes. See pheno-type.

Germ cell. A cell with a potential to form a zygote, i.e., a functional spermatozoon or ovum.

Gonad. An organ in either male or female in which reproductive cells are proliferated and developed; a testicle or an ovary.

Graafian follicle. The small sac in which the ovum is developed in the ovary and which, after the discharge of the ovum, becomes the corpus luteum (q.v.).

Gynander. An organism (usually insect) which is part male and part female, the most common type having the male and female areas delineated along the median line of the body, rarely if ever found in the dog.

Haploid. The number of chromosomes in spermatozoa and ova after meiosis; one-half of the diploid number.

Heredity. The tendency of an organism to reproduce itself.

Hermaphrodite. An organism that has the reproductive organs of both sexes.

Heterosis. The superiority over either or both parents of the progeny resulting from the crossing of strains, varieties, breeds or species. Known also as hybrid vigor.

Heterozygous. Not pure or true breeding for a given factor. Containing two different alleles of the same gene. A heterozygote produces two kinds of germ cells with respect to the gene in question.

Homozygous. Pure or true breeding for a given character. Having the gene for the character in duplicate, a homozygote produces only one kind of germ cell with respect to that gene.

Hormone. A secretion from any one of the ductless or endocrine glands.

Hybrid. (1) The offspring of two parents of unlike genetic makeup. (2) A heterozygote for one or more genes.

Hymen. The thin membrane which partially closes the vagina in virgins, not present in the virgin bitch; the maidenhead.

Identical twins. Litter brothers or sisters (always of the same sex) which develop from the same ovum and spermatozoon, as distinguished from fraternal twins.

Impotence. The inability to perform the sexual act; not to be confused with sterility.

Inbreeding. The mating together of closely related animals.

Incomplete dominance. In an organism which is heterozygous in respect to any allelic pair, there is a failure of either gene to obscure the potential of the other; also called partial dominance.

Influence of previous sire. See telegony.

Interstitial gland. The endocrine gland of the gonad, the hormones of which affect the development of secondary sex characters.

In whelp. Pregnant (said of the bitch).

Lamarckism. The theory, now largely discredited, that acquired characters may be transmitted through heredity; from Lamarck who promulgated that belief.

Lethal. The name given to a gene which, when present in the homo-zygous condition, causes the death of the embryo. When the inherited condition is one which leads to premature death after birth, it is more correctly called sub- or semi-lethal.

Line breeding. The mating together of animals somewhat related, but less closely related than in inbreeding.

Linkage. The tendency for two or more characters to be transmitted together, because the genes are located in the same chromosome.

Mammal. An animal of a species which suckles its young; a member of the biological Order Mammalia.

Maturation. The development of the germ cells, including the reduction division in which the number of chromosomes is halved from the diploid to the haploid number, and the further mi to tic division of the cells.

Mendelism. The theory embodied in the First and Second Laws of Mendel which establishes that characters are inherited as entities and independently one of another due to segregation and the independent assortment of the genes.

Menstruation. The periodic discharge of blood or bloody fluid from the uterus of any female mammal, occurring in connection with or in preparation for ovulation.

Metabolism. The process by which living cells in plants and animals are continually worn out by use and build themselves up again by means of food.

Meiosis. The process of cell division occurring in the germ cells that reduces the chromosome count by one-half; reduction division.

Mitosis. The process of cell division in which the chromosomes split lengthwise that the resultant daughter cells may each possess the full diploid number of chromosomes.

Modifiers. Genes which by themselves have no noticeable effects, but influence the effects of other genes present in the same organism.

Monohybrid. The progeny from two parents which differed genetically in respect to a single allelic pair.

Monorchidism or Monorchism. A condition in which one of the testes has failed to descend into the scrotum.

Mutation. Heritable germinal variation of abrupt origin that is passed on to the progeny; may be only a minor variation or may result in a trait much dissimilar from ancestral stocks. So-called sport.

Natural Selection, The Theory of. The organisms likely to have more descendants are those whose genetic variations are most advantageous as adaptations to their way of life and to their particular environment.

Non-disjunction. The failure of the members of any pair of chromosomes to separate in the reduction division of maturation which results in both members of the pair going to one of the daughter cells.

Nucleolus (pi. nucleoli). Small bodies formed in the nucleus of the cell.

Nucleus. The central body within the cell containing the chromosomes.

Oestrus. Heat; breeding "season."

Oogenesis. The growth and development of the sex cell of the female into an ovum.

Oogonia. The cells which are proliferated from the primordial germ cells of the female organism which after reduction and mitosis develop into ova.

Orgasm. The climax of the sexual act.

Os uteri. The mouth of the uterus; the opening between the vagina and the uterus. •

Out breeding . The mating together of unrelated animals.

Ovary. The organ of the female in which the ova develop.

Oviducts. The passages by which the ova are conveyed from the ovaries to the uterus; Fallopian tubes.

Ovum (pi. ova). The functional reproductive cell produced by the female; an egg.
P1. The parent generation; P2 grandparent generation, etc.

Parthenogenesis. Reproduction from the ovum without its union with a sperm.

Parturition. The act of bringing forth young; whelping.

Pedigree. A record of the ancestry or line of descent.

Penis. The male organ of copulation.

Period of gestation. The duration of normal pregnancy; in the dog about sixty-three days.

Phenotype. The appearance and/or performance of an individual, i.e., the outcome of the interaction between its genotype and its environment.

Pisum. The genus which includes the common garden pea, such as was used experimentally by Mendel in the discovery of his laws. Pituitary gland. A tiny endocrine gland in two lobes (anterior and posterior) attached to the base of the brain of all vertebrates, the various hormones from which affect growth and reproduction. Placenta. The organ in the higher mammals by which the fetus is attached to the wall of the uterus and through which it is nourished and waste products are removed from it. The main part of the afterbirth.

Placental mammalia. Those mammals whose young develop in the uterus and are there nourished through a placenta; the biological Sub-Order of Eutheria.

Polar body. A small, nonfunctional cell cast off by the ovum after reduction division.

Polyhybrid. The progeny from parents which differed in several or many Mendelian characters.

Prenatal impression. The alleged influence upon the fetus of the experiences and sensations of the mother in the course of her pregnancy.

Propontent . Said of an animal with an unusually strong tendency to pass its characteristics on to its offspring. Probably due to the presence of many dominant alleles in the proponent parent. Primary Oocyte. The germ cell of the female immediately prior to its reduction division.

Primitive streak. A scar-like line along the midline of the back of the early embryo.

Pronucleus. The nucleus of a gamete either male or female.

Protoplasm . The vital substance of all plant or animal life.

Pure dominant. See homozygous.

Recessive (gene or character). A character which is undeveloped or buried when the gene for it develops from only one parent and is associated in the zygote with its dominant allelomorph.

Reduction division. See meiosis.

Reproductive cells. Cells set aside in the development of the organism, the function of which is to reproduce it; the cells of the germ plasma in contradistinction to the somatoplasma .

Reversion. The reappearance of ancestral traits not found in the more immediate several generations of ancestors; "throwing back"; atavism.

Scrotum. The pouch in which the testes are suspended.

Secondary sexual characters. Attributes which are normally limited to a single sex, but which have no primary part in reproduction. Examples, beard of the human male, the ornate tail of the peacock.

Secondary spermatocyte. The male germ cell immediately after its reduction division, which divides by mitosis to form spermatids.

Segregation. Manifested in the F2 (and later hybrid generations) as a separation and distribution to different individuals of the Mendelian characters in which the parents of the ¥x hybrid differed.

Semen. Fluid containing innumerable spermatozoa which is produced by the generative organs of the male and by which impregnation is effected.

Sex chromosomes. The X and Y chromosomes which carry the determiners for sex.

Sex-limited trait. A trait (usually a secondary sex trait) which manifests itself in one sex and is either absent or greatly reduced in the other. Sex-limited genes are in the autosomes, not in the sex chromosomes.

Sex-linked trait. A trait for which the determiner is on the sex chromosomes; specifically, a trait carried by a gene or genes in the non-homologous portion of the X chromosome. Traits carried in the homologpus portions of the X and Y chromosomes are said to be incompletely sex-linked.

Siblings. Two or more progeny of the same parents irrespective of sex or time of birth.

Somatic. Of or pertaining to the body cells in contradistinction to the reproductive cells.

Species. A group of animals or plants, usually making up a subdivision next smaller than a genus, having certain characteristics which distinguish it from any other group and which are usually inherited. The common criterion for a species is that its members are interfertile.

Spermatozoon, (pi. spermatozoa). The male gamete; a single sperm.

Sperma+id. A germ cell of the male resultant from the splitting of the secondary spermatocyte; the stage of spermatogenesis immediately prior to the spermatozoon.

Spermatogenesis. The development of spermatozoa from the primary sex cells.

Spermatogonia. The cells which are proliferated from the primordial germ cells of the male organism and which, after reduction and mitosis, develop into spermatozoa.

Sphincter cunni. Muscles of the vagina of the bitch which grasp the corpus cavernosum of the dog, the penis, in coitus and render impossible the withdrawal of that organ until erection subsides.

Spindle. A formation within the cell at one stage of mitosis.

Sterility. The inability or failure to produce live gametes; barrenness; not to be confused with impotence.

Strain. A more or less numerous family of the same breed, the members of which are more or less interrelated one to another and which exhibit a uniformity of type which distinguishes them from members of other strains. See also breed and variety.

Synapsis. The pairing of the chromosomes prior to the reduction division of the sex cell.

Telegony. The alleged influence of a previous sire on the progeny produced by a subsequent sire from the same mother.
Testicle. See testis.

Testis (pi. testes). The male sex gland in which the spermatozoa develop; testicle.

Trait. See character.

Trihybrid. A hybrid of which the parents differed in respect to three characters.

Umbilical cord. The cord which connects the fetus with its mother and through which it receives nutriment and oxygen; the navel cord.

Unisexual. Of one sex; of or pertaining to plants or animals having organs of but one sex.

Unit character. A character which is heritable independently of other characters.

Urethra. The duct by which urine is discharged from the bladder.

Uterus. The organ of a female animal in which the fetuses are protected and developed before birth; the womb.

Vagina. The passage in the female from the uterus to the exterior orifice.

Variety. A group of animals, usually domesticated, with distinguishing traits as opposed to other varieties; larger than a strain but smaller than a breed.

Vas deferens. The duct by which the semen is conveyed from the epididymis.

Vulva. The exterior opening of the genital organs of the female.

Whelp. (1) To give birth to young (applied to the bitch); (2) a puppy or young dog.

Womb. See uterus.

X-Chromosome. One of the two kinds of the sex chromosomes of which, in the higher animals, the female cell possesses two, the male cell but one, plus a Y-Chromosome. See Y-Chromosome.

Y-Chromosome. The sex chromosome which is found only in the male cells of the higher animals and determines maleness in the zygote of which it is a part. See also X-Chromosome.

Zoology. The branch of biology which deals of animals.

Zygote. The cell and the resultant organism which results from the union of the ovum and spermatozoon.

Are You Ready To Move Onto The Next Lesson? Click Here...