Cattle genetics 101

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aussie_cowgirl

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In light of a lot of discussions and arguments regarding genetics I decided to do up a little info thread about it. Hopefully it’s useful to some of you. If you have any further questions feel free to mail me.

Cattle have 30 pairs of chromosomes, of these 29 are called autosomes and the remaining pair are sex chromosomes (ie XX being female or XY being male). During breeding, one chromosome of each pair from each parent is passed onto the progeny. So half of the calf’s genetics come from the mother, half from the father. If the calf is a female, it means it received an X chromosome from her mother and an X chromosome from her father. Alternatively, if it was a male, he would have received an X chromosome from his mother and a Y chromosome from his father.

DNA is like the instruction manual for an organism. Each gene is responsible for something different in the animal. In each animals DNA there are 2 possible versions (known as alleles) of the gene.
Which allele is expressed in the animal is determined by which allele is more dominant. Dominant alleles are expressed even when another different allele is present. For a recessive allele to be expressed, BOTH alleles present for the gene MUST be the recessive one.
If an animal has 2 matching alleles (whether it be dominant or recessive) it is none as homozygous (homo= same). If an animal carries 2 different alleles it is known as heterozygous (hetero= different).
Here are some artistic renditions I made in paint 
punnetsquare.jpg

punnetsquare2.jpg

punnetsquare3.jpg

*****there is an error, the black cow in the last image should be 'heterozygous black'*****

To add to this confusion there are 2 types of white alleles. The white allele belonging to the Charolais is actually a red allele with a ‘masking gene’. And the white allele belonging to the shorthorn is a white gene. Seeing as the allele is actually red, the colour is recessive. But from a Charolais x you can get grey, smokey, dun etc colours. This is caused by the masking gene, or more commonly known as the diluting gene which is dominant. The white allele in a Shorthorn is co-dominant with red and black. So homozygous shorthorn will only be Red or white, and a heterozygous shorthorn will be a roan. When crossed with a black animal you often get a black/blue roan which means the calf is heterozygous and has received a black and a white allele.

As mentioned earlier there is a diluter gene that alters coat colour further which is a dominant allele. Yellow cattle are red with a diluter gene present. Mousey brown cattle/grey cattle are black with a diluter gene. There is variation within colours, from pale yellow-orange and mousey brown-silver-grey.
The allele for ‘polling’ in cattle is dominant to the allele for horns. I.e


1 Polled Bull(PP) x Horned Cow (hh)= 100% poll 0% horned
2 Polled Bull(Ph) x Horned Cow(hh)= 50% poll 50% horned
3 Polled Bull(Ph) x Polled Cow(Ph)= 75% poll 25% horned
4 Polled Bull(PP) x Polled Cow(PP)= 100% poll 0% horned
5 Polled Bull(PP) x Polled Cow(Ph)= 100% poll 0% horned

Edit (thanks Dun):In some bos indicus type cattle there are 2 genes controlling horns. Along with the regular horned/polled gene there is a gene called the African horn gene (Af; polled is An) (which appears on the sex genes. The Y chromosome doesn't carry a matching allele so in males, there is only one allele. Therefore they are more susceptible).
Homozygous (Af Af) cattle always have horns.
Heterozygous (Af An); females will be polled, males will be horned
Homozygous (An An) Always polled

How it works with the regular horn/poll gene
AfAfPP and AfAfPp Horned cow and Horned bull
AfAnPP and AfAnPp Polled cow or Horned bull
AnAnPP and AnAnPp Polled cow and Polled bull
AfAfpp, AfAnpp and AnAnpp Horned cow and Horned bull
 

dun

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And then there is the African horn gene, usually shown as An.
 

bigag03

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Horn/Poll is probably not a subject for the Genetics 101 board (maybe not even the 401 board). There are still too many unknowns. The existance of the African Horn gene is not disputed, but its mode of inheritance is still largely unknown (sex linked is likely, but still not confirmed). Also, you have not even touched on scurs which could be controlled by several different genes with epistatic effects controlling the expression (and probably very breed specific).
Just my 2 cents.
 

alexfarms

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bigag03":ifr29v7j said:
Horn/Poll is probably not a subject for the Genetics 101 board (maybe not even the 401 board). There are still too many unknowns. The existance of the African Horn gene is not disputed, but its mode of inheritance is still largely unknown (sex linked is likely, but still not confirmed). Also, you have not even touched on scurs which could be controlled by several different genes with epistatic effects controlling the expression (and probably very breed specific).
Just my 2 cents.

I'll second that. I have read more theories on genetics than I can count that claimed to have found THE answer, and many are later discarded. The inheritance of scurs is a good example and many times scurs are mistaken for horns.
 
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aussie_cowgirl

aussie_cowgirl

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Cattle genetics itself is still a frontier. The fact that in a heterozygous animal females are polled, males are horned logically point to being a sex linked gene. (Well genetic logic any way). I need to reed a bit more into scurs and I'll update. I was just getting the colour out of the road because that's the dispute.
 

randiliana

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aussie_cowgirl":njoazvy0 said:
Cattle genetics itself is still a frontier. The fact that in a heterozygous animal females are polled, males are horned logically point to being a sex linked gene. (Well genetic logic any way). I need to reed a bit more into scurs and I'll update. I was just getting the colour out of the road because that's the dispute.

Have to disagree with you on the roan gene, it isn't co-dominant, it is another modifying gene. It just modifies the appearance of the red or black gene, like the dilutor genes do, and there are several of those as well. 2 that are fairly well understood, and several that aren't so well understood.
 
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aussie_cowgirl

aussie_cowgirl

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i dont know where you have read that because i have always been brought up with it being co-dominant. and all the text i find on it also lists the shorthorn roan as an instance of codominance.
http://www.microbiologyprocedure.com/ge ... inance.htm
http://www.hsc.csu.edu.au/biology/core/ ... 33net.html (about 2/3 down)
http://www.nhvweb.net/vhs/Science/HMcdo ... obs-hm.htm
(bottom of the page)
roan cattle has always been known as a codominance of red and white alleles. I talked about how charolais are different. I didn't go into breeds like british white but i think that isn't needed in basic stuff.
 

VanC

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aussie_cowgirl":i7w7018b said:

aussie_cowgirl: Lots of people find this stuff boring, but I've always found it fascinating. Thank you. Must've been a lot of work. The above graphic is incorrect, however. Homozygous black crossed with heterozygous black will yield all black calves. Only if both parents are heterozygous will there be a chance for red calves. I'm sure this was just an oversight on your part since it's obvious you know a lot more about this stuff than I do. ;-)
 

randiliana

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aussie_cowgirl":pu73jkxy said:
i dont know where you have read that because i have always been brought up with it being co-dominant. and all the text i find on it also lists the shorthorn roan as an instance of codominance.
http://www.microbiologyprocedure.com/ge ... inance.htm
http://www.hsc.csu.edu.au/biology/core/ ... 33net.html (about 2/3 down)
http://www.nhvweb.net/vhs/Science/HMcdo ... obs-hm.htm
(bottom of the page)
roan cattle has always been known as a codominance of red and white alleles. I talked about how charolais are different. I didn't go into breeds like british white but i think that isn't needed in basic stuff.


The roan gene is similar to the hereford gene it is not co-dominant, but incompletely dominant. Incompletely dominant means that when a trait is Homozygous, it is expressed differently than when it is heterozygous, hence you have white cattle when they are homo for roan and roan cattle when they are hetero for roan. If the roan gene were co-dominant, it should express itself the same way regardless of whether it is homo or hetero.

A couple of links

http://www.braunviehcenter.com/cattle_g ... part2.html

An Excerpt from the above link

Shorthorns, Texas Longhorns, and Florida Crackers carry a gene, R, responsible, when heterozygous, for roan color. Roan coloration is a mixture of pigmented and white hairs. When homozygous for R, a nearly entirely white animal is produced with some pigment expressed within the ears. While the most often observed roan is red, the roan gene acts equally effectively in the removal of any pigment. Thus, blue roans, Ed_Rr+, can be produced by crossing white or roan Shorthorn with Angus. The expression of the roan gene when heterozygous is highly variable, with some animals being roan over the entire body, while in others, roaning may be restricted to just the center of the forehead

http://www.sss-mag.com/fernhill/cowcolor.html

http://animalscience.ag.utk.edu/beef/pd ... DK2004.pdf
 

hillsdown

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Thank you ladies for all of your time and effort ... :clap:

But Aussie and Randi you are making my head hurt :help: ....I think I will study more of this in the summer when cows are out on pasture and my head is not so full..Until then if I have a question I will just post it for you gals to figure it out... :lol2:

Great posts and links thank you... :wave:
 

Keren

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The way I learned it, there is a difference between incomplete dominance, and co-dominance.

With incomplete dominance, you have

RR being red
WW being white and
RW results in PINK

With co-dominance, you have

RR being red
WW being white and
RW being both red and white ie ROAN
 

DOC HARRIS

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Just for the interest of some of you with whom I have discussed the fact that I raised Chinchilla's some years ago, the incredibly SMASHING WHITE fur of the underbelly of the Agouti (Standard Grey) Chinchilla was dictated by 14 different Alleles!! It was the almost impossible "BURDEN of Selection" of breeding stock to attempt to blend all of the genes together to arrive at the MOST optimal matching to achieve the Whitest of WHITE, and at the same time retain the spectacularly HIGH number of fur hair follicles per square inch without losing the agouti fur pattern! I even attempted to develop an Artificial Insemination protocol for "Chins" to accelerate the development process!

Didn't work!

DOC HARRIS
 

KNERSIE

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15 posts on genetics and no-one has even mentioned quantitative inheritance when that type of inheritance is the one controlling just about all of the economical important traits like BW, WW, YW, milking ability, SC, ADG, etc?!
 

bigag03

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The fact that in a heterozygous animal females are polled, males are horned logically point to being a sex linked gene. (Well genetic logic any way).

And if that were ALWAYS true, I'd agree with you 100% but there are too many animals that don't fit. Females that should be polled are horned and vice versus. Every time the researchers thought they had it figured out they have discovered another animal that didn't fit the model.
 

alexfarms

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I have had numerous Angus breeders tell me that scurred animals don't necessarily carry the horned gene. Maybe that is true in the Angus breed, but I doubt it. The old American Polled Hereford Association had a Superior Sire Program in which bulls were genetically tested in various ways and one of the qualifications for becoming a Superior Sire was the bull had to be proven to be a 100% dehorner through matings to horned cows. In the history of the Superior Sire Program not one scurred bull tested was proven to be a 100% dehorner. I have made this challenge before and no one has ever answered it YET: Tell me one scurred bull that has been PROVEN to be a non-carrier of the horned gene. In most breeds scurred bulls are discarded, but in the old APHA some top notch scurred bulls were tested, if they weren't top bulls they probably would never have been kept...So please don't start the argument about "scurrs are a sign of superiority". IF someone can tell me of a proven 100% dehorner that is scurred, then I will start to believe the notion that there is no linkage between the presence of scurrs and the presence of the horned gene. With the current dna tests for horns, it looks to me like a 100% dehorning, scurred bull ought to have been identified.
 

KNERSIE

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alexfarms":1q0h3dnv said:
I have had numerous Angus breeders tell me that scurred animals don't necessarily carry the horned gene. Maybe that is true in the Angus breed, but I doubt it. The old American Polled Hereford Association had a Superior Sire Program in which bulls were genetically tested in various ways and one of the qualifications for becoming a Superior Sire was the bull had to be proven to be a 100% dehorner through matings to horned cows. In the history of the Superior Sire Program not one scurred bull tested was proven to be a 100% dehorner. I have made this challenge before and no one has ever answered it YET: Tell me one scurred bull that has been PROVEN to be a non-carrier of the horned gene. In most breeds scurred bulls are discarded, but in the old APHA some top notch scurred bulls were tested, if they weren't top bulls they probably would never have been kept...So please don't start the argument about "scurrs are a sign of superiority". IF someone can tell me of a proven 100% dehorner that is scurred, then I will start to believe the notion that there is no linkage between the presence of scurrs and the presence of the horned gene. With the current dna tests for horns, it looks to me like a 100% dehorning, scurred bull ought to have been identified.

I've tried in vain to get factually correct information on scurs, most of the research is quite old and not a single paper came to a concise answer. For a long time I believed the sex linkage to be correct, but that has recently been proved wrong in my herd or atleast not exactly correct. A smooth polled cow had a lightly scurred heifer and a smooth polled bull calf the next year, if the sex linkage was correct the bullcalf must have atleast one scurred allel and should have been scurred.

I am currently doing an experiment in a neighbours herd of mostly horned herefords and some of my polled bulls. So far a scurred bull has sired about 60% horned calves and not a single scurred calf. A smooth polled bull has sired 100% polled, but its still too early to tell with certainty whether he sired some scurs or not. Previously I've used homozygous polled bulls that never sired a scurred calf, hopefully this bull at the neighbours will also do this to atleast give me a better indication what to expect as far as scurs go in homozygous polled bulls.

For the time being I have seen nothing that has proved my theory, of all scurred bulls are heterozygous, wrong.
 
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