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Outcross calculator

How much of the original line comes back.

Each generation bred back to the original line halves what is left of an outcross: 50% at F1, then 75%, 87.5% and 93.75%. Choose a foundation parent and an original-line parent to see every generation to F5.

Instrument No. 002 · The outcross register · Example animals

One line per generation, from foundation outcross back to the line.

LineEnteredBred fromOriginal lineExpected COI
Desert WickSRA 20-118 · admitted as foundationAdmitted from source registry A0%0%
Ridgeview Lumen of the WickRSR-2022-2385F0 × Ridgeview line animal50%0%
Ridgeview Ash of the WickRSR-2023-9939F1 × Ridgeview line animal75%9%
Ridgeview Lantern of the WickRSR-2024-7694F2 × Ridgeview line animal87.5%13.5%
Ridgeview Ember of the WickRSR-2025-4189F3 × Ridgeview line animal93.75%15.75%
Ridgeview Cinder of the WickRSR-2026-1015F4 × Ridgeview line animal96.875%16.875%

F3 · Ridgeview Lantern of the Wick · Example data

87.5%

of the original line, with an expected COI of 13.5% when bred to an average Ridgeview line animal.

The line itselfF0F1F2F3F4F5
% of original lineExpected COI, as a share of the line’s own 18%

p(Fn) = (p(Fn−1) + 100%) / 2 · COI(Fn) ≈ p(Fn−1) × 18%

Method: each offspring carries the average of its parents’ % of original line. Expected COI assumes mates are average animals of the line and the foundation is unrelated to it. Example data.

Halving the gap

Each generation bred back to the line halves what is left of the outcross: 50%, 75%, 87.5%, 93.75%, 96.875%.

Why COI climbs again

The more of the line an animal carries, the more it shares with its mate. Expected COI follows one generation behind.

Your club sets the threshold

When an outcross descendant counts as original line again is your club’s rule, written in its bylaws.

How it works

The arithmetic, in the open.

Average of the parents

Each offspring carries the average of its parents’ % of original line. A foundation animal starts at 0%; an original-line animal at 100%.

Bred back each generation

Breeding back to original-line animals halves the gap every generation: 50%, 75%, 87.5%, 93.75%.

Your club sets the line

When an animal counts as original line again is your club’s rule, not the calculator’s.

Reading the register

What each column of the register tells you.

Each row is one sample animal, from the foundation at F0 to its descendant at F5.

Line and Entered

The generation, counted from the foundation at F0, and the animal’s sample name and registration number.

Bred from

F0 has no parents on the page: it is admitted from its source registry. From F1 on, an animal’s two parents are the generation before it and an animal of the original line.

Original line

The share of the animal’s pedigree that traces back to the original line.

Expected COI

From F1 on, the animal’s own expected COI, worked from its two parents and the line’s own COI. The 0% at F0 is a placeholder, not a figure worked from a pedigree.

Past the sample

The same rule, beyond the sample animals.

Any generation

After n generations bred back, what is left of the outcross is 100% halved n times, and the original line is the rest. At F6 that is 1.5625% outcross and 98.4375% original line.

Two descendants bred together

Breeding two outcross descendants to each other gives the average of their shares. Two animals at 75% give 75%, so the share rises only when the mate carries more of the original line.

A related foundation

If the foundation shares ancestors with the line, real COI can run higher than the expected COI shown.

Opening the studbook covers when a board considers it and what to write down so the next board can read the decision.

Questions

Questions about outcross percentages.

What percentage of the original line does an F4 carry?
93.75%, when each generation from the foundation is bred to an original-line animal. An F4 is four generations from the foundation outcross, so 6.25% of its pedigree traces to the outcross.
How many generations until an outcross descendant counts as purebred?
There is no single answer. Your club’s rules set the point, as a generation or as a share of the original line. The register above shows the share at each generation to F5.
Do the percentages change with the line or foundation I choose?
No. The share of original line depends only on how many generations have been bred back, so that column is the same for every choice. The choices change the rest of the sample: the line sets the expected COI from its own COI, and both choices change the sample animals’ names, numbers and Bred from entries.
Why is expected COI 0% at F1?
The calculator assumes the foundation shares no ancestors with the line, so an F1’s two parents are unrelated. From F2 on, the parent from the outcross side carries part of the line, and expected COI rises toward the line’s own COI.
Is the percentage what a DNA test would show?
Not exactly. It is the share expected from the pedigree. Each parent passes on half of its genes, drawn at random, so one animal’s actual share can sit above or below the figure. The calculator reads no DNA results.
Can I work out my own animals here?
Not directly. The lines, animals and registration numbers are sample data, and the page has no field for your own. To work out a real animal, average its two parents’ shares of the original line, one generation at a time.