Repeated ancestors in a cat pedigree can provide valuable information about how a breeding line was developed.

Repeated ancestors in a cat pedigree can provide valuable information about how a breeding line was developed. They may reveal a deliberate attempt to preserve certain breed characteristics, but they may also indicate a reduction in genetic diversity or an increased probability that the same inherited variants will meet in the offspring.

For this reason, a breeder should not read a pedigree as a simple list of famous names and titles. Before planning a mating, it is important to compare the sire’s and dam’s ancestry, identify shared ancestors, consider how closely they occur and evaluate the proposed combination together with health, temperament, fertility and previous progeny information.

What does a repeated ancestor in a pedigree mean?

A repeated ancestor is a cat whose name appears more than once within the pedigree being studied. When the same animal is found in both the sire’s and the dam’s ancestry, it creates a relationship between the proposed parents.

The importance of that relationship depends on several factors:

• how close the common ancestor is to each parent;
• how many times the ancestor is repeated;
• whether several related animals from the same family are also present;
• how complete the pedigree is;
• whether the common ancestor was itself inbred;
• what health, fertility, temperament and conformation information is available about the line.

A name appearing once in the fourth generation of one parent and once in the fifth generation of the other usually has a different influence from an animal appearing repeatedly in the second and third generations.

Linebreeding and inbreeding: what is the difference?

In genetic terms, both linebreeding and close inbreeding involve mating related animals. The word linebreeding is generally used when the breeder intentionally concentrates the influence of a selected ancestor or family while trying to avoid the closest possible combinations.

The breeding intention may be different, but the pedigree mechanism remains relatedness. Calling a mating “linebreeding” does not remove the need to calculate its expected coefficient of inbreeding or to study possible inherited risks.

Linebreeding may make certain characteristics more predictable because it increases genetic uniformity. However, the same process can also increase the probability that undesirable recessive variants inherited from a common ancestor will be expressed.

What is the coefficient of inbreeding?

The coefficient of inbreeding, commonly abbreviated as COI, estimates the probability that an offspring will inherit two copies of an allele that are identical by descent from a common ancestor.

COI should not be interpreted as:

• the percentage of “bad genes” in a cat;
• a diagnosis of hereditary disease;
• a guarantee that kittens will be unhealthy;
• a complete measurement of all genetic diversity within a breed;
• a replacement for health testing and professional breeding analysis.

It is a probability based on the pedigree information included in the calculation. If ancestors are missing, entered incorrectly or excluded because only a few generations are analysed, the calculated result may underestimate the true relationship.

Expected COI in close relationship examples

Under simplified pedigree assumptions, where the common ancestors are themselves unrelated and not inbred, the following combinations produce these expected values:

Real pedigrees are often more complicated. Several common ancestors may be present, the same family may appear through multiple paths and earlier generations may already contain linebreeding. Therefore, the complete COI may be higher than the value suggested by one visible relationship.

Why the number of generations matters

A COI calculated over three or four generations describes only the relationships visible within those generations. It does not prove that the cats are unrelated beyond that point.

For meaningful comparison, breeders should use the same pedigree depth for all proposed matings. Whenever reliable information is available, a deeper pedigree provides a more complete picture.

It can be useful to record two figures:

• COI calculated over a fixed number of generations, allowing different matings to be compared consistently;
• COI calculated from the complete available pedigree, showing the broader documented relationship.

The generation depth should always be written next to the result. A figure such as “COI 4%” is incomplete unless the reader knows whether it was calculated over four generations, ten generations or the entire available pedigree.

How to analyse a planned mating step by step

1. Confirm the identity of both cats

Check registered names, registration numbers, breeds, colours and parent information. Similar names, spelling differences and renamed imported cats can create errors during comparison.

2. Place the pedigrees side by side

Compare the sire’s and dam’s pedigrees generation by generation. Mark every animal appearing on both sides. Do not rely only on cattery names, because cats from the same cattery are not necessarily close relatives, while related cats may carry different cattery prefixes.

3. Record the position of every common ancestor

Write down where each common ancestor occurs. For example, an ancestor may appear in the sire’s third generation and the dam’s fourth generation. This provides more useful information than simply writing that the animal is “present in both pedigrees.”

4. Look for repeated families, not only one name

A pedigree may contain several siblings, parents and descendants from the same family. Even when one individual name is not repeated many times, the pedigree may still concentrate a closely related group.

5. Calculate the expected COI

Use a pedigree database or calculator that can recognise all valid paths to common ancestors. Record the pedigree depth and do not compare results calculated using different numbers of generations as though they were equivalent.

6. Study health and reproductive history

Review breed-relevant health examinations, DNA test results where appropriate, longevity, fertility, litter size, neonatal survival and known causes of death. A low COI does not compensate for ignoring a known hereditary risk.

7. Evaluate temperament and breed type

A breeding plan should consider the whole cat. Temperament, structure, movement, coat, colour, body condition and conformity to the breed standard remain important. Genetic diversity should be preserved without losing sight of the health and functional characteristics of the breed.

8. Review previous offspring

If either cat or the repeated ancestor has produced earlier litters, study the results. Look not only at the best show offspring but at the entire litter: health, development, bite, fertility, temperament, structural faults and consistency of type.

Why the lowest possible COI is not the only goal

Choosing the mating with the lowest available number is not automatically the best breeding decision. A very low pedigree COI cannot correct poor health information, incompatible breed type, serious temperament problems or an unsuitable genetic test combination.

At the same time, repeatedly using a small group of popular breeding cats may gradually narrow the breed’s gene pool, even when each individual mating appears acceptable when viewed separately.

Responsible breeding therefore requires balance. The breeder should consider:

• the expected COI of the litter;
• the existing COI of both parents;
• the completeness of the pedigree;
• the frequency of the same family within the population;
• health and DNA information;
• fertility and longevity;
• temperament;
• breed-standard qualities;
• the long-term value of the planned offspring.

Warning signs requiring closer evaluation

Additional caution is appropriate when:

• the same ancestor appears repeatedly in the first few generations;
• several close relatives from one family dominate both sides of the pedigree;
• the pedigree contains missing or unverified ancestors;
• there is a history of reduced fertility, small litters or neonatal losses;
• similar congenital defects have appeared in related litters;
• the mating is planned only to reproduce the appearance of one famous cat;
• the breeder cannot explain the purpose and expected benefit of the combination.

These signs do not establish a diagnosis, but they show that more information is needed before making a breeding decision.

What should be recorded in the cattery breeding journal?

For each proposed mating, record:

• the full registered names and numbers of both cats;
• the date on which the pedigrees were analysed;
• the number of generations reviewed;
• all significant common ancestors;
• the calculated COI and calculation depth;
• the purpose of the mating;
• health and genetic test information;
• expected strengths and possible risks;
• alternative partners that were considered;
• the results of the litter after birth and development.

This transforms a pedigree from a decorative document into a practical breeding instrument.

A pedigree should support a long-term breeding strategy

Repeated ancestors must be interpreted, not simply counted. A breeder should understand why an ancestor is being repeated, what that animal contributed to the line and what risks may also be concentrated.

The most responsible decision is rarely based on one famous name, one title or one percentage. It is based on verified pedigree information, knowledge of the cats and their relatives, health data, breed standards and a clear long-term breeding goal.

Useful WCA resources:

• WCA Pedigree Check;
• Order a WCA Pedigree Online;
• What Is a WCA Pedigree?;
• WCA Recognized Breeds and Breed Standards;
• WCA Rules.