Cytogenetics.— A branch of biolog\’ that deals with 
the study of heredity and \ariation hy the metli- 
ods of i)oth cytology (the study of cells) and 
genetics. 
Cytoplasm.— The protoplasm of a cell, e.xternal to 
the cell's nuclear memhrane. 
Diploid.— .A cell with double the basic chromosome 
number. 
D\A (deoxyribonucleic acid).— The genetic ma- 
terial found in all li\ ing organisms. K\ ery inher- 
ited characteristic has its origin somewhere in 
the code of each indi\ idual's complement of I3\',A. 
Gene.— The hereditary unit; a segment of DNA 
coding for a specific protein. 
Gene expression.— The manifestation of the ge- 
netic material of an organism as specific traits. 
Genetic drift.— Changes of gene frequency in small 
population due to chance preserx ation or extinc- 
tion of particular genes. 
Genetic code.— The biochemical basis of heredity 
consisting of codons (base triplets along the DNA 
se(iuence) that determine the specific amino acid 
sequence in proteins and that are the same for all 
forms of life studied so far. 
D\.-\ vector.— A \ehicle for transferring DN.A from 
one cell to another. 
Dominant gene.— .A characteristic whose expres- 
sion pre\ ails o\ er alternati\ e characteristics for a 
gi\en trait. 
Blscherichiit coli.—.\ bacterium that commonly in- 
habits the human intestine. It is a fa\orite orga- 
nism for many microbiological experiments. 
Endotoxins.— Complex molecules (lipopolysaccha- 
rides) that compose an integral part of the cell 
wall, and are released only when the integrity of 
the cell is disturbed. 
Embryo transfer.— Implantation of an embryo 
into the o\ iduct or uterus. 
Enzyme.— .A functional protein that catalyzes a 
chemical reaction. Enzymes control the rale of 
metabolic processes in an organism; they are the 
acti\ e agents in the fermentation process. 
Estrogens.— Female sex hormones. 
Estrus (“heat”).— The period in which the female 
will allow the male to mate her. 
Eukaryote.— A higher, compartmentalized cell 
characterized by its extensive internal structure 
and the presence of a nucleus containing the 
DNA. .All multicellular organisms are eukaryotic. 
The simpler cells, the prokaryotes, ha\e much 
less compartmentalization and internal struc- 
ture; bacteria are prokaryotes. 
Exotoxins.— Proteins produced by bacteria that are 
able to diffuse out of the cells; generally more po- 
tent and specific in their action than endotoxins. 
Fermentation. — The biochemical process of con- 
\erting a raw material such as glucose into a 
product such as ethanol. 
Fibroblast.— A cell that gives rise to connective 
tissues. 
Gamete.— A mature reproductive cell. 
Genetic engineering.— A technologv' used at the 
laboratory level to alter the hereditary apparatus 
of a li\ ing cell so that the cell can produce more 
or different chemicals, or perfoi m completely 
new functions. These altered cells are then used 
in industrial production. 
Gene mapping.— Determining the relative loca- 
tions of different genes on a gi\ en chromosome. 
Genome.— The basic chromosome set of an 
organism— the sum total of its genes. 
Genotype.— The genetic constitution of an individ- 
ual or group. 
Germplasm.— The total genetic variability available 
to an organism, represented by the pool of germ 
cells or seed. 
Germ cell.— The sex cell of an organism (sperm or 
egg, pollen or ovum). It differs from other cells in 
that it contains only half the usual number of 
chromosomes. Germ cells fuse during fertiliza- 
tion. 
Glycopeptides.— Chains of amino acids with at- 
tached carbohydrates. 
Glycoprotein.— A conjugated protein in which the 
nonprotein group is a carbohydrate. 
Haploid.— A cell with only one set (half of the usual 
number) of chromosomes. 
Heterozygous.— When the two genes controlling a 
particular trait are different, the organism is 
heterozygous for that trait. 
Homozygous.— When the two genes controlling a 
particular trait are identical for a pair of chro- 
mosomes, the organism is said to be homozygous 
for that trait. 
Hormones.— The "messenger” molecules of the 
body that help coordinate the actions of various 
tissues; they produce a specific effect on the ac- 
tivity of cells remote from their point of origin. 
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