# Where does the 1/4\*V\_D and 1/2\*V\_A come from?

**URL:** https://isgw-forum.colorado.edu/t/where-does-the-1-4-v-d-and-1-2-v-a-come-from/621
**Category:** Twin & family modeling
**Created:** [March 5, 2024, 7:08pm UTC](https://isgw-forum.colorado.edu/t/where-does-the-1-4-v-d-and-1-2-v-a-come-from/621 "2024-03-05T19:08:51Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![davide](https://isgw-forum.colorado.edu/letter_avatar_proxy/v4/letter/d/258eb7/32.png) [@davide](https://isgw-forum.colorado.edu/u/davide)
#### Post date: [March 5, 2024, 7:08pm UTC](https://isgw-forum.colorado.edu/t/where-does-the-1-4-v-d-and-1-2-v-a-come-from/621/1 "2024-03-05T19:08:51Z")

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Hi Everyone,  
In response to yesterday’s question I’ve created a video to explain where these coefficients come from:  
[https://www.colorado.edu/ibg/biometrical-genetics](https://www.colorado.edu/ibg/biometrical-genetics)  
The video is about 45 minutes but explains everything from first principles. I hope it is useful.  
cheers  
Dave

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### Author: ![Ralph\_Porneso](https://isgw-forum.colorado.edu/user_avatar/isgw-forum.colorado.edu/ralph_porneso/32/559_2.png) [@Ralph\_Porneso](https://isgw-forum.colorado.edu/u/Ralph_Porneso)
#### Post date: [March 15, 2024, 1:09pm UTC](https://isgw-forum.colorado.edu/t/where-does-the-1-4-v-d-and-1-2-v-a-come-from/621/2 "2024-03-15T13:09:09Z")

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Hi Dave,

Finally had the chance to look into this after the workshop – it’s so clearly explained! I only wanted to know where the 1/4 V\_D came from and I got so much more from this video lecture, so thank you very much! I especially appreciate the additional resources at the end.

Best regards,

Ralph

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### Author: ![davide](https://isgw-forum.colorado.edu/letter_avatar_proxy/v4/letter/d/258eb7/32.png) [@davide](https://isgw-forum.colorado.edu/u/davide)
#### Post date: [February 23, 2025, 10:43pm UTC](https://isgw-forum.colorado.edu/t/where-does-the-1-4-v-d-and-1-2-v-a-come-from/621/3 "2025-02-23T22:43:42Z")

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Hi Ralph  
So sorry to not reply to you- I’ve only looked at this forum again this year (2025!). You can think of the 1/4\*V\_D intuitively coming from the fact that (a) dominance effects at genotypes will only be correlated between siblings when they share the same genotype, and (b) siblings share the same genotype only 1/4 of the time. Hope this helps?!  
cheers  
Dave