Page 1 of 1
Posted: Sat Sep 02, 2006 6:32 am
by Kathy Millar
My apologies for asking this question which must have been asked before but: is the dwarf gene recessive or dominant? A local breeder here is scared that her Dexters may be carrying it around unbeknownst to her (ie. the gene is recessive) but I think that is not the case. I am not aware of any short-legged Dexters locally but I guess there are a few in some of the Canadian pedigrees. What can I tell her to put her mind to rest? (I know you would need to breed a short to a short to possibly get a bulldog calf but I think she is worried that her animals could be "carriers: of the gene). ???
Kathy
Posted: Sat Sep 02, 2006 10:53 am
by Duncan MacIntyre
The chondrodysplasia gene will only show as bulldogs if it is inherited from both parents, so in that sense it is recessive. However if one gene is present, there is the effect that gives us the traditional short legged dexter. The vast majority of these can be picked out by an experienced eye but height alone is not sufficient as there are large "short legs" and small "long legs" with some overlapping. If individual animals give rise to any doubt the DNA test is always available, using hair with follicles or blood. the DCS in UK uses a Dutch laboratory, I am not sure about Canada and USA.
On thing is certain, if both parents were non carriers, then the offspring cannot possibly carry the gene. So in our own herds if we use only non carriers for breeding we will not have the gene. Having said that we might well choose to have animals tested officially to have proof for others eg buying animals, or semen, embryos etc.
In my own Burnside herd I am trying to produce non carriers which are the same height as traditional short legged dexters, using a bull of pure Woodmagic breeding though he carries a different prefix, Shilton Pontius. I hope to have him, a daughter and two grand-daughters at Westmorland show on 14th September if anyone in north of England is interested. I do not expect to be carrying off any prizes, but would like to show that "long legged" dexters do not need to resemble giraffes.
Duncan
Posted: Sat Sep 02, 2006 12:12 pm
by Penny
Good for you, Duncan. I wish you the best of luck.
Hopefully, I may get there if all is quiet on the farm.
Posted: Sat Sep 02, 2006 1:15 pm
by Woodmagic
Well done Duncan, would love to be able to visit Westmoreland, hope it goes well. The Canadian Society has a system for DNA chondrodysplasia testing, and if there is genuine worry this is undoubtedly the best answer. I am very keen that folks do not bred for legginess in order to avoid the recessive.
Posted: Sat Sep 02, 2006 4:42 pm
by Carol K
In the USA our Lab used for the Chondro. test is Bova - Can, who are in Canada. So maybe tell them to contact John Potter who handles all our tests if they would like to test their animals. If you need John's email it is available from the ADCA web site http://www.dextercattle.org/ .
Posted: Sun Sep 03, 2006 4:27 pm
by Kathy Millar
OK, so what you are saying, Duncan, that all the short-legged Dexters are heterozygous and only when you get a homozygous individual will a bulldog result. I do understand that some "short" Dexters may be leggier and look like a non-short especially to an inexperienced eye. I know I sure had problems picking out non-shorts when I was in Britain. We just don't see short-legged animals here so I have a hard time with all this. My point is, that perhaps there are some carriers around here and we just don't know it. I would like to see all the Dexter organizations stamp out this gene in the breed and with the new test, it can be done.
Kathy
Posted: Sun Sep 03, 2006 5:29 pm
by Woodmagic
Kathy all short legged Dexters when they carry the bulldog are heterozygous, i.e. mixed breeders, for the bulldog.
Their calves where two mixed breeders are mated together, stand a chance of getting like genes from
each parent, giving them a pair of identical genes, unlike their parents. If they inherit the bulldog gene from
both parents the result is a bulldog, if the two genes are for a normal skeleton you will have a true breeder and a live calf, the length of leg will vary, due to breeding I spent years breeding for a shorter leg without using the bulldog gene to do it. If there is doubt the sensible answer is the DNA test. The true breeder or homozygous animal can never produce a bulldog calf. Unfortunately where short leg breeding is practiced , a bigger heterozygous animal can look very close to the homozygous breeder, and judging by eye becomes difficult.
Posted: Sun Sep 03, 2006 10:00 pm
by Liz D
The test here is just hair folicles, done by Bova-Can, through our association. If your neighbour is worried about having carriers, it's easy to find out, but one thing that is a sure pointer, other than 'look' is the offspring size of her cow and her cow's dam. A carrier doesn't breed true, meaning that the gene that causes the dwarf or shortness actually 'hides' up to 6" of true height in the line when a non-carrier is produced ...so if some of the offspring are a lot taller than others, maybe they should test. Anyway that is 'anecdotal' at best and really if they are worried the test is easy and not expensive if you have only a couple of cows to do... adds up if you have a lot. Liz
Posted: Tue Sep 05, 2006 11:27 am
by Inger
The C gene certainly does hide the true phenotype Liz. The calves sired by our carrier bull (BD1) are some of the longest legged calves in our herd.
I have since found out that the average height in his family line is actually on the tall side for Dexters. But he sure put the beefiness back in the rumps of his offspring. Which is the reason I bought him. They should sell well at the sales yards. :D
Posted: Mon Mar 12, 2007 9:22 am
by TONY CUTTEN
The Chondroplasia gene test has been available in New Zealand and Australia for several years now. Two alleles are present in new Zealand and Australia BD1 and BD2. One is the common UK bulldog allele and the other is thought to have been brought in(introgression) from another cattle breed in early crossings in the 1970,s. Many Dexter breeders are now testing their bulls for BD1 and/or BD2.
Posted: Mon Mar 12, 2007 11:35 am
by Inger
Hi Tony, nice to see you're joining in too. 
Posted: Tue Mar 13, 2007 3:24 am
by Kirk- Cascade Herd US
Kathy Millar wrote:Is the dwarf gene recessive or dominant? A local breeder here is scared that her Dexters may be carrying it around unbeknownst to her (ie. the gene is recessive) but I think that is not the case.
Kathy
The official term for chondrodysplasia's genetic standing is Incomplete Dominance (or partial dominance).
There are three primary types of dominance:
1. Simple or Complete Dominance (Polled and Black are examples) This is where the dominant gene completely overrides any recessives. In this case, recessives can hide.
2. Incomplete Dominance (chondrodysplasia is an example) This is where a heterozygous genotype creates an intermediate phenotype, halfway between both types.
3. Co-Dominance. I can't think of an example in cattle, but in flowers, if red and white are co-dominant, then a flower with one red gene and one white gene would be white AND red speckled showing both types. But if red were incompletely dominant to white, a flower with one red gene and one white gene would be pink, halfway between red and white.
In dexters, chondrodysplasia is incompletely dominant to the wild-type non-chondrodysplasia. So a homozygous individual with two chondro genes is a bulldog (lethal), while an individual with one chondro gene and one wild-type (non-chondro) gene is intermediate between bulldog and normal wildtype.
So Dexters must exhibit the chondrodysplasia gene because it is Incompletely Dominant and is not recessive and it cannot hide. It cannot skip generations.
Hope this makes sense.
Kirk
Cascade Herd (US)
Posted: Thu Apr 12, 2007 11:27 am
by Inger
I've just found out that one of our heifers is a BD1 carrier. It was a bit of a surprise to me, as, although she was smaller, her legs between knee and hoof, didn't look that short. The BD2 variant seems to be more noticable that the BD1 gene. We have had two BD2 carrying cows and a BD1 carrier bull to compare against each other. Although bulls can be more difficult to pick, as they appear to have shorter legs because of the larger amount of muscle that they carry. At least that's what I find anyway.