618 GENETICS IN RELATION TO AGRICULTURE 
has been derived from only one of the two generating gametes. Both eggs and sperms 
produced by such an individual are typically of two kinds, half of them containing 
the factor in question, the rest lacking this factor; consequently the offspring of hetero- 
zygous individuals usually consist of a mixture of individuals some of which possess 
the corresponding character while others lack it. 
Homosynapsis.—As applied to the sex-chromosomes, the pairing of two X- or 
two W-chromosomes. 
Homozygosis.—The state of being homozygous; the extent to which an individual 
is homozygous. 3 
Homozygote.—A homozygous individual. 
Homozygous.—That condition of an individual in which any given genetic factor 
is doubly present, due usually to the fact that the two gametes which gave rise to 
this individual were alike with respect to the factor in question. Such an individual 
having been formed by the union of like gametes, in turn generally produces gametes of 
only one kind with respect to a given character, thus giving rise to offspring which are, in 
this regard, like the parents; in other words, homozygous individuals usually breed true. 
Hormone.—A substance secreted or found in some organ or tissue and carried 
thence in the blood to another organ or tissue which it stimulates to functional activity 
or whose functions it inhibits. 
Hybrid.—The offspring of animals or plants of different genotypes, varieties, 
species, or genera. 
Hypertrophy.—An enlargement of a part of the body from excessive growth or 
multiplication of its elements. 
Indigenous.—Native, not exotic. 
Inter se.—Between or among themselves. 
Interference.—Protection from coincident crossing-over of loci on either side of 
the point of crossing-over. 
In utero.—In the uterus or womb. 
Lethal.— Destructive of life. 
Linkage.—That type of inheritance in which the factors tend to remain together 
in the general process of segregation; ‘‘gametic coupling’’ of the older terminology. 
Locus (pl. loci).—A definite point or region in a chromosome at which is located 
a genetic factor or gene. 
Lymantria.—A genus of moths. 
Meiosis.—See reduction or heterotypic division. 
Metabolism.—The sum of the chemical changes within the body, or within any 
single cell of the body, by which the protoplasm is either renewed or changed to per- 
form special functions, or else disorganized and prepared for excretion. 
Mitosis.—Indirect cell division, the characteristic method of multiplication of 
somatic cells, in which each chromosome is halved longitudinally, one-half passing 
to each daughter cell. 
Monecious Plants.—Those having both sexes in the same plant. 
Morphology.—The branch of biology concerned with the outer form and internal 
structure (without regard necessarily to the functions) of animals and plants. 
Multiple Allelomorphs.—Factors occupying the same locus of homologous 
chromosomes; the characters conditioned by such factors. ; 
Mutant.—An individual of a genotypic character differing from that of its parent, 
or those of its parents, and not derived from them by a normal process of segregation 
or by crossing-over. 
Mutation.—The result of a change in genotypic nature independently of normal 
segregation or of crossing-over; strictly an alteration in the fundamental nature of a 
genetic factor. 
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