The history of record keeping in mouse colonies is, in part, the history of the development of inbred strains of mice. The genealogy, family tree, or pedigree of the DBA strains traces back to 1909. The C57 strains owe their origin to the record of matings of two mice at Cold Spring Harbor in 1921 ( Chapter 1). The pedigrees of these strains are valuable not only for their length but also for their extensive history of the strains and sublines of the strains in the intervening decades.
A record-keeping system for inbred lines and various experimental colonies must enable the investigator to trace the collateral relatives, ancestors, and progeny of any animal with ease. Many systems have been devised for use with colonies of mice ( Dickie, 1963; Porter and Lane-Petter, 1962). Any investigator who wishes to start keeping records on a colony may study the various systems, decide what sorts of information he wishes, what is essential for accurate maintenance of an inbred line and for various types of experimental colonies, and what will be most efficient and least cumbersome. In this chapter we shall review the basic components of the systems, including ledgers, pedigree or record cards, pedigree charts, cage tags, and card files ( Figure 3-1). The first two components are essential in building pedigree charts; the latter two provide efficient tools for managing colonies.
IDENTIFICATION SYSTEM AND LEDGER
The first essential for a record-keeping system is a source of sequence numbers which may be a continuous series, a code, or an evolving-number system. A continuous number series may be entered in a ledger beginning with 01 (or 0001 or 0101 if a punched card system is to be used) and continuing to 99. Thereafter the numbers are 101 to 199, 201 to 299, and so forth. Note that 100, 200, and so forth are omitted, since such numbers would mean unmarked animals in the usual ear-marking system. The animals are marked with an ear punch according to the code shown in Figure 3-2. In some cases a hole punched in the center of the ear may be used to denote zero. The center hole is used primarily so that each ear will be punched whether the number is 07 or 70.
Toe clipping is also a successful means of identification but is not in very widespread use. It is more common to clip toes of animals at birth to signify classification of some condition such as a transitory anemia that will be unrecognizable at the time of weaning. Tail clipping is often used to mark animals treated in some way shortly after birth. This is useful not only to distinguish them from all other litters or animals in adulthood, but also to distinguish treated from untreated members of the same litter. Painting has been used to identify mice of albino strains but this practice is not recommended. Each of the other methods is more permanent.
Ledgers are usually bookkeeping ledgers or spiral-bound notebooks. A ledger may be used for each strain or mutant stock or, in small colonies, for all animals of several stocks. The ledger includes the following information:
A line of the ledger is used for each individual in the litter. At the beginning of the record for a litter the ancestry, generation, parentage, and birth date of the litter are recorded, a line is drawn across the page under the notations for the last animal in the litter. The record for a subsequent litter begins on the next line. Therefore one can see at a glance, by study of the ledger, the disposition of any particular litter.
Some systems employ a ledger for each stock and assign each mating a double-page space for all information concerning offspring of that mating. When this system is used, a modified numbering or code system is used for identification.
It is essential to enter the phenotype or genotype when recording mutant stocks and various experimental animals. When such notations are made, the symbol + is standard for wild-type or nonmutant alleles. This information is noted after the sex of the animals.
At The Jackson Laboratory the production of mice on a large scale takes place in three steps: Foundation Stocks (FS), a small primary source for inbreeding control without subline differentiation; Pedigreed Expansion Stocks (PES), for expansion to large numbers of breeding pairs in a few generations; and Production Stocks (PS), where all progeny are harvested for use in research. An evolving-number system and a master ledger are used to identify the breeding units in all three colonies. If FS, each breeding pair is given a four-digit serial number such as 0352 from a master ledger, the source of numbers for all strains. When weanling pairs are transferred from FS to PES, they are given an additional single-place number separated from the serial number of the parents by a hyphen, such as 0352-1, 0352-2, ..., which identifies the serial order of the pairs made up from the 0352 pair in FS. The 10th pair is designated as 0352-0; the 11th through 20th pairs are designated by the addition of the same serial numbers, but each is encircled, the 21st through the 30th pairs may, if necessary, be designated by the addition of the same single serial numbers enclosed in squares.
When the pairs transferred to PES from FS in turn reproduce, the pairs made up from their progeny are designated by serial numbers in the second position, such as 0352-11, 0352-12,..., 0352-21, 0352-22,.... The second position is thus used for serial numbers of matings two generations removed from the FS, just as the first position designated serial numbers of matings one generation removed. The third, fourth, ... positions may thus be used for enumerating matings in the third, fourth,... generations removed from FS.
When breeding pairs are transferred from PES to PS, another number is added, separated by a hyphen. Thus 0352-131-6 is the sixth mating in PS, following three generations of matings in PES of descendants of pair 0352 in FS ( Figure 3-3).
This evolving-number system shows (1) the source pair in FS, (2) the location of any particular mating, i.e., whether it is from FS, PES, or PS, and (3) the number of generations the mating has been separated from FS.
PEDIGREE CARD AND CAGE TAG
In some systems two cards are used, a mating card and a litter card. In this instance the use of the ledger is omitted and the identification of animals evolves from the litter cards.
When inbred strains are being maintained (always brother-sister matings), it is unnecessary to provide an individual card for the male since all data for the female are applicable to the male and neither will be mated again. In breeding experiments it is advisable to have a pedigree card for each mate so that each may be moved from pen to pen, as required, without confusion or loss of information.
Cage tags are mainly of two types: those providing only location on the shelf and those providing not only the location but also information such as the identification numbers of the animals in the pen, or number of mice in the pen, and any other information desired. In large breeding colonies it has proved efficient to have the cage tag or card serve as the pedigree card and thus eliminate one record-keeping step. In this case the basic information desired on the pedigree card is placed on the cage card. When it is necessary to have several strains of similar phenotype (e.g., several albino strains) in one room, cage cards of different colors and with different patterns on the top border of the card provide an extra measure of security against mix-ups. A color and pattern system can be devised so that no two strains identical in appearance will be next to each other, since cards of similar color and pattern would not ordinarily be next to one another ( Figure 3-4).
Keypunch and keysort cards may be used as pedigree cards or as cage cards to eliminate time-consuming transfers of data in large-scale summaries and analyses of breeding records.
Several systems for maintenance of card files have been used. If all the pedigree cards in one file pertain to one strain, they may be filed in sequence according to pen number, dam or sire number, or parental birth date. A birth date file is especially useful when large numbers of pairs must be replaced at regular intervals.
When the colony is small and there is a variety of strains, stocks, or experimental animals, it is more efficient to use file guide cards which correspond to cage numbers. In some colonies it is useful to divide the cards into three groups, each group marked by an appropriate guide card labeled mated, pregnant, and litters (with oldest litters at front of group). This system provides a continuous check on the status of the colony.
Pedigree charts are necessary in maintaining inbred strains. They must be used to insure that a strain is propagated through a single pair in each generation and that sublines are prevented from developing and coexisting for many generations. The charts may contain any additional information desired for selection of the main line such as tumor occurrence, litter size, number of litters, and time between generations. These charts need only contain the female number and should be kept current with the matings in the pens. Pedigree charts are also useful in determining relationships of deviants that may arise in a colony, learning about their inheritance, and eliminating carriers of mutations from the colony.
The components of record-keeping systems are ledgers, pedigree cards, pedigree charts, and cage tags. Methods of using these components in various record-keeping systems have been described. Use of these components in these systems should provide the basic objective of easy traceability of ancestors, collateral relatives, and progeny of each animal.
Dickie, M.M. 1963. Methods of keeping records, p. 522-537. In W.J. Burdette [ed.] Methodology in Mammalian Genetics. Holden-Day, San Francisco.
Porter, G. and W. Lane-Petter. 1962. Notes for Breeders of Common Laboratory Animals, p. 96. Academic Press, London and New York.