Factor (maker), a name given to the hypothetical something, the independently inheritable element in the germ-cell, whose presence is necessary to the development of a certain inherited character or characters or contributes with other factors to the development of a character. "Gene" and "determiner" are sometimes used as synonyms of factor.
Feeble-mindedness, a condition in which mental development is retarded or incomplete. It is a relative term, since an individual who would be feeble-minded in one society might be normal or even bright in another. The customary criterion is the inability of the individual, because of mental defect existing from an early age, to compete on equal terms with his normal fellows, or to manage himself or his affairs with ordinary prudence. American students usually distinguish three grades of mental defect: Idiots are those who are unable to take care of themselves, even to the extent of guarding against common physical dangers or satisfying physical needs. Their mentality does not progress beyond that of a normal two-year-old child. Imbeciles can care for themselves after a fashion, but are unable to earn their living. Their mental ages range from three to seven years, inclusive. Morons, who correspond to the common acceptation of the term feeble-minded, "can under proper direction become more or less self-supporting but they are as a rule incapable of undertaking affairs which demand judgment or involve unrestricted competition with normal individuals. Their intelligence ranges with that of normal children from seven to twelve years of age." There is necessarily a considerable borderline, but any adult whose intelligence is beyond that of the normal twelve-year-old child is usually considered to be not feeble-minded.
Gamete (mate), a mature germ-cell; in animals an ovum or spermatozoön.
Genetics (origins), for a long time meant the study of evolution by experimental breeding and was often synonomous with Mendelism. It is gradually returning to its broader, original meaning of the study of variation and heredity, that is, the origin of the individual's traits. This broader meaning is preferable.
Germinal (sprig), due to something present in the germ-cell. A trait is germinal when its basis is inherited,—as eye color,—and when it develops with nothing more than the standard environment; remaining relatively constant from one generation to another, except as influenced by reproduction.
Germ-Plasm (sprig form), mature germ-cells and the living material from which they are produced.
Hæmophilia (blood love), an inability of the blood to clot. It thus becomes impossible to stop the flow of blood from a cut, and one who has inherited hæmophilia usually dies sooner or later from hæmorrhage.
Heredity (heirship), is usually considered from the outside, when it may properly be defined as organic resemblance based on descent, or the correlation between relatives. But a better definition, based on the results of genetics, looks at it as a mechanism, not as an external appearance. From this point of view, heredity may be said to be "the persistence of certain cell-constituents (in the germ-cells) through an unending number of cell-divisions."
Heterozygote (different yolk), a zygotic individual which contains both members of an allelomorphic pair.
Homozygote (same yolk), an individual which contains only one member of an allelomorphic pair, but contains that in duplicate, having received it from both parents. A homozygous individual, having been formed by the union of like gametes, in turn regularly produces gametes of only one kind with respect to any given factor, thus giving rise to offspring which are, in this regard, like the parents; in other words, homozygotes regularly "breed true." An individual may be a homozygote with respect to one factor and a heterozygote with respect to another.