# Do DZs always share 1/4 of Dominant variance?
**URL:** https://isgw-forum.colorado.edu/t/do-dzs-always-share-1-4-of-dominant-variance/787
**Category:** Day 3
**Created:** [June 3, 2026, 8:22pm UTC](https://isgw-forum.colorado.edu/t/do-dzs-always-share-1-4-of-dominant-variance/787 "2026-06-03T20:22:27Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@anonymous](https://isgw-forum.colorado.edu/u/anonymous)
#### Post date: [June 3, 2026, 8:22pm UTC](https://isgw-forum.colorado.edu/t/do-dzs-always-share-1-4-of-dominant-variance/787/1 "2026-06-03T20:22:27Z")
Do DZs always share 1/4 of Dominant variance?
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### Author:  [@anonymous](https://isgw-forum.colorado.edu/u/anonymous)
#### Post date: [June 3, 2026, 8:22pm UTC](https://isgw-forum.colorado.edu/t/do-dzs-always-share-1-4-of-dominant-variance/787/2 "2026-06-03T20:22:36Z")
for dominance yes (think punnet squares) but this could also be used to model epistatis and then it would be \<.25
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### Author:  [@davide](https://isgw-forum.colorado.edu/u/davide)
#### Post date: [June 4, 2026, 9:05pm UTC](https://isgw-forum.colorado.edu/t/do-dzs-always-share-1-4-of-dominant-variance/787/3 "2026-06-04T21:05:07Z")
The expected term is 1/4 (which is why we use 0.25 in the ADE model)- but there is variation around this value.
Just like we have used the estimated proportion of alleles identical by descent across the genome (“pihat”) to model the additive genetic variance in DZ twins, we could also use the estimated proportion of genotypes shared between DZ twins across the genome, to estimate the dominance genetic variance. Power is typically low to estimate V\_D.
Check out:
[Assumption-Free Estimation of Heritability from Genome-Wide Identity-by-Descent Sharing between Full Siblings | PLOS Genetics](https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.0020041)