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How many Test Crosses are needed

Posted: Thu Oct 05, 2017 9:48 am
by Vetrock
I can't find anyone to give me a straight answer on this. If I wanted to prove a bull was homozygous for a certain gene (for instance the black gene in an Angus bull), how many test crosses are required to prove such? Does anyone have a number?

Re: How many Test Crosses are needed

Posted: Thu Oct 05, 2017 11:33 am
by Son of Butch
I don't know if there is a straight answer to 100% certainty.
It's possible 1 cross can prove a bull is not.
My estimate is 16 would put you in the range of 94% certainty and it would take many more to reach 99.4%
DNA test would tell you heterozygous or homozygous to 100% certainty and you would know much faster.

Re: How many Test Crosses are needed

Posted: Thu Oct 05, 2017 12:45 pm
by Franke
Breeding to what cows? a set of blacks? reds? whites? chocolates? Then you could have diluter genes? Like SoB said DNA would be the easiest to know for certain.

Re: How many Test Crosses are needed

Posted: Thu Oct 05, 2017 3:18 pm
by Jake
I believe the number they used to use for genetic testing before DNA was breeding to 20 daughters. I might be wrong on this it may have been 30 but pretty sure it's one of those two.

Re: How many Test Crosses are needed

Posted: Thu Oct 05, 2017 3:55 pm
by Caustic Burno
Son of Butch wrote:I don't know if there is a straight answer to 100% certainty.
It's possible 1 cross can prove a bull is not.
My estimate is 16 would put you in the range of 94% certainty and it would take many more to reach 99.4%
DNA test would tell you heterozygous or homozygous to 100% certainty and you would know much faster.


A lot depends on the breed of cow as well as several breeds don't play by the rules.

Re: How many Test Crosses are needed

Posted: Thu Oct 05, 2017 7:15 pm
by dun
I don;t know how many is required but I know 16 isn;t enough. Granny was a black Angus red carrier. Bred to either a Polled Hereford, red Fleck or a Red Angus the first year she calved for us she had a red heifer. The next 16 calves were all black.

Re: How many Test Crosses are needed

Posted: Fri Oct 06, 2017 2:34 am
by Son of Butch
dun wrote:I don;t know how many is required but I know 16 isn;t enough. Granny was a black Angus red carrier.
Bred to either a Polled Hereford, red Fleck or a Red Angus the first year she calved for us she had a red heifer.
The next 16 calves were all black.

She was proven heterozygous black by having a red calf in her first 16 tries... so in her case it was enough.
Just because her 17th calf was black doesn't mean the next 4 wouldn't all have been red.
Besides 93.75% (aka about 94%) is not 100%

16 crosses = 93.75% and 16 is the lowest number I would feel comfortable at calling him proven
20 = 95%
25 = 96%
30 = 96.666%
50 = 98%
To reach 99.4% certainty would take 167 crosses and yet there is still a minute chance the 168th calf would be red.
Without DNA testing you just have to pick the most reasonable number at which you feel comfortable.

Trivia:
97.37% probability of picking the wrong number on one spin of a Roulette Wheel

Re: How many Test Crosses are needed

Posted: Fri Oct 06, 2017 6:20 am
by dun
Son of Butch wrote:
dun wrote:I don;t know how many is required but I know 16 isn;t enough. Granny was a black Angus red carrier.
Bred to either a Polled Hereford, red Fleck or a Red Angus the first year she calved for us she had a red heifer.
The next 16 calves were all black.

She was proven heterozygous black by having a red calf in her first 16 tries... so in her case it was enough.
Just because her 17th calf was black doesn't mean the next 4 wouldn't all have been red.
Besides 93.75% (aka about 94%) is not 100%

16 crosses = 93.75% and 16 is the lowest number I would feel comfortable at calling him proven
20 = 95%
25 = 96%
30 = 96.666%
50 = 98%
To reach 99.4% certainty would take 167 crosses and yet there is still a minute chance the 168th calf would be red.
Without DNA testing you just have to pick the most reasonable number at which you feel comfortable.

Trivia:
97.37% probability of picking the wrong number on one spin of a Roulette Wheel

The point was that even 16 may not mean anything. In her case 17 would have been enough

Re: How many Test Crosses are needed

Posted: Fri Oct 06, 2017 7:12 pm
by Air gator
I remember reading somewhere that if you wanted to check a bull for genetic defects you had to breed him to 13 of his daughters. Not sure if that is the same.

Re: How many Test Crosses are needed

Posted: Fri Oct 06, 2017 9:23 pm
by Chocolate Cow
http://onpasture.com/2014/10/20/breedin ... -breeding/
Before the advent of genetic testing for recessive traits the only way to statistically ensure genetic “purity” of a bull/ram/buck etc. was to breed that bull to 35 of his own daughters concurrently. If no genetic defects show up in any of the offspring, the bull is 99.7% likely to be genetic defect free.

Re: How many Test Crosses are needed

Posted: Fri Oct 13, 2017 6:56 pm
by CSM
In the case of homozygous polled, breeding to 10 horned cows and getting 10 polled calves, 99.9% accuracy. I would think breeding to 10 red cows and 10 black calves would be the same accuracy. It would be quicker to have him tested if it is important to you.

Re: How many Test Crosses are needed

Posted: Fri Oct 13, 2017 7:35 pm
by Son of Butch
CSM wrote:In the case of homozygous polled, breeding to 10 horned cows and getting 10 polled calves, 99.9% accuracy.

Correct for polled gene when both breeds are British. (any zebu blood screws everything up)
2 of 2 = 75% probability of being homozygous
4 of 4 = 93.75%
6 of 6 = 98.44%
10 of 10 = 99.90%
14 of 14 = 99.99%


Gene for scurs is another matter as it's transmitted separately with no relationship to whether horned or polled.
Not all horned cattle carry the scur gene and not all polled cattle are free of it.

Re: How many Test Crosses are needed

Posted: Tue Oct 31, 2017 11:43 am
by mpassmore85
Dependant on exact trait you are trying to prove is homozygous?

You know his lineage at least 2 generations both parents ?

Color is always tricky lots of purebred and hybrid cows that are “refined” or a bit steer looking are homozygous also.

So in that you get luck of the draw normally when you breed homo to homo you get a 40/20 split as opposed to a 30/30

Re: How many Test Crosses are needed

Posted: Tue Oct 31, 2017 12:01 pm
by Caustic Burno
Son of Butch wrote:I don't know if there is a straight answer to 100% certainty.
It's possible 1 cross can prove a bull is not.
My estimate is 16 would put you in the range of 94% certainty and it would take many more to reach 99.4%
DNA test would tell you heterozygous or homozygous to 100% certainty and you would know much faster.


If I remember correctly after that it had to breed true for four generations as well was in there somewhere in my college biology.
Now that was a long long time ago.

Re: How many Test Crosses are needed

Posted: Tue Oct 31, 2017 2:20 pm
by ALACOWMAN
Has anyone noticed the double set of eyelashes on polled and homo..polled cattle, as opposed to single on the horned??