Backcross, selfing & sib-mating
Pedigree expectations by generation: recurrent-parent share for BX lines, homozygosity for S lines, inbreeding for F lines.
Generation
BX1 = F1 crossed back to the recurrent parent
These are pedigree expectations: averages across the genome. Any one seedling can sit well above or below them; only a genetic test measures the real figure.
Result
Expected recurrent-parent share at BX3
93.75%
- BX175%
- BX287.5%
- BX393.8%
- BX496.9%
- BX598.4%
How this is calculated
Backcross
BXn recurrent-parent share = 1 − 0.5^(n+1) (pedigree expectation)
Selfing
Each selfing halves heterozygosity: homozygous share = 1 − 0.5^n (from fully heterozygous start)
Full-sib mating
F_t = (1 + 2F_(t−1) + F_(t−2)) / 4 for one full-sib pair per generation (Falconer & Mackay)
- Assumes a single brother × sister pair each generation. Selecting from larger populations raises F more slowly.
- Source for the recurrence: Falconer DS & Mackay TFC (1996), Introduction to Quantitative Genetics, 4th ed. (textbook; not yet in the grow library).
Cited targets
From the genetics.guru grow library, in the units each source used. Grades: strong and moderate are peer-reviewed; community practice is untested.
recurrent parent genome share BC1breeding75% expectedStrong
1 - (1/2)^(n+1); expectation, not a measurement
1 source
recurrent parent genome share BC2breeding87.5% expectedStrong
1 - (1/2)^(n+1); expectation, not a measurement
1 source
recurrent parent genome share BC3breeding93.8% expectedStrong
1 - (1/2)^(n+1); expectation, not a measurement
1 source
recurrent parent genome share BC4breeding96.9% expectedStrong
1 - (1/2)^(n+1); expectation, not a measurement
1 source
recurrent parent genome share BC5breeding98.4% expectedStrong
1 - (1/2)^(n+1); expectation, not a measurement
1 source
heterozygosity after n selfing generations from F1breedingNot establishedStrong
F2 chemotype segregation (BT/BD selfed)breedingNot establishedStrong
codominant B locus; class II ratio family-specific
1 source