Backyard Poultry Forum • View topic - Shairlyn's Genetics Lessons

Backyard Poultry Forum

Chickens, waterfowl & all poultry - home of exhibition & backyard poultry in Australia & New Zealand
Login with a social network:
It is currently Tue May 23, 2017 6:09 am

All times are UTC + 10 hours [ DST ]




Post new topic Reply to topic  [ 35 posts ]  Go to page Previous  1, 2, 3  Next
Author Message
PostPosted: Wed Jan 14, 2015 1:19 pm 
Offline
Deluxe Drake
Deluxe Drake

Joined: Fri Aug 08, 2008 9:31 pm
Posts: 2452
Location: Canberra
Here are a couple of handy tools I've found on the web.

A Punnet Square calculator that will do up to five genes: http://scienceprimer.com/punnett-square-calculator

A list of just about every chicken colour and shape gene ever mentioned: http://sellers.kippenjungle.nl/page3.html
(a few have been disproven or shown to be the same as another gene so be sure to read the notes).

_________________
Brindabella Pekins


Last edited by shairlyn on Thu Jan 15, 2015 5:33 pm, edited 1 time in total.

Top
 Profile  
 
PostPosted: Thu Jan 15, 2015 12:48 pm 
Offline
Deluxe Drake
Deluxe Drake

Joined: Fri Aug 08, 2008 9:31 pm
Posts: 2452
Location: Canberra
Dominant White

I thought that it was time to mention that there are two 'white' genes, the second being 'Dominant White'. It is a completely different gene to that which gives us Recessive White. The gene is the I gene, and the recessive allele 'i+' is that which is most common and causes normal colouration. The dominant allele 'I' restricts the black pigment, turning black to white.

Back when many breeds were being created, there would have been no way for breeders to know for certain that there were two different types of white, and I imagine that conflicting observations on inheritance might have caused a few punch-ups down at the pub.

Leghorns, we now know, are made white by Dominant White.
Image

However the allele is a little leaky and Dominant White bird on Extended Black will have some black flecks on their feathers. It also shows a small amount of incomplete dominance, whereby a bird that is heterozygous I/i+ will show more black flecks than a bird that is homozygous I/I. In leghorns the pure white colour is achieved by adding genes like Columbian Co and Dark Brown Db which further restrict the black pigment.

In the days before commercial hybrids there was a popular egg-producing cross in Australia called an 'Austra White'. It was made by putting a Leghorn (E/E, I/I) rooster over an Australorp (E/E, i+/i+) hen. I know that there is some work being done to produce these lovely birds again. This produces the genotype E/E, I/i+ and also reduces the other black pigment restrictors from the Leghorn. The Austra Whites look like this. Pretty aren't they?:
Image

Interestingly, Dominant White I is not the only allele for this gene. There are two others and they both dilute black to a lesser extent. One is Dun 'Id', and one is Smokey 'Is'. Both produce birds with a delicate grey shade and I confess I'm not up on the subtleties of the colours myself, but I understand they are quite different. This is a Dun bird:
Image

Both Smokey and Dun are dominant over the wildtype 'i+' and I believe that work is being done to determine how they relate to each other and Dominant White in terms of which is most dominant.

So whilst there are four possible alleles for this gene, any given bird can only have two of them, and we usually breed so that they have two copies that are the same. Remember that Recessive White 'c' is an allele of a completely different gene. It is possible for a bird to have both Dominant and Recessive White!

What is interesting about Dominant White is that it only affects the black pigment, whilst Recessive White affects both. What this means is that on a bird that has a pattern with both black and gold pigments, you can use Dominant White to turn the black sections white. This is used to great effect in several breeds.

We can turn the Wheaten bird:
Image

Into a Pile bird:
Image

Or we can take a Laced Wyandotte:
Image

And turn it into a Buff, white Laced (probably the wrong nomenclature):
Image

The bird above could also be Splash-laced, a double dose of blue would have the same effect.

_________________
Brindabella Pekins


Top
 Profile  
 
PostPosted: Thu Jan 15, 2015 1:44 pm 
Offline
Fiesty Fowl
Fiesty Fowl

Joined: Fri Jul 09, 2010 12:20 pm
Posts: 1128
Location: Thirlmere nsw
Iam really enjoying this post as didn't know the colours or bases for chickens. I use for parrots a site called gencalc.com 1.3 and it gives most colours with their alle symbols or if dom,rec etc and you just select the dots and it includes splits when you generate it it gives all outcomes in % for both sexs. I wonder why they didn't use this for chooks as well, if not suitable with the box system the idea that 1.0 is the cock and 0.1 is the hen is usable. with this you could set the standard and put at the top 1.0 (cock) and on the side 0.1 (hen) thanks Mycoola.


Top
 Profile  
 
PostPosted: Fri Jan 16, 2015 8:04 pm 
Offline
Deluxe Drake
Deluxe Drake

Joined: Fri Aug 08, 2008 9:31 pm
Posts: 2452
Location: Canberra
Deducing a bird’s genotype – a case study

I’d like to talk a bit more about deductive genotyping – working out the genes that a bird carries based on its appearance and progeny. As previously commented, birds very inconsiderately don’t come with a little label detailing their genes, and we are forced to do our own investigative work. Where the bird comes from a line that we have bred for several generations we often have a very good idea of their genes; where the bird is a recent acquisition things can be much less clear.

There was a recent, very interesting conversation regarding a bird acquired for colour breeding, which I’d like to use as a case study; an example of how we can go about doing some deductive genotyping. I’ve probably simplified the case a bit, but hopefully I have the salient points correct.

A breeder and BYP member had recently acquired what they believed to be a Splash hen, in the hopes of introducing Blue into their current black line. The hen had the appropriate phenotype, white with black spots. She was put to the breeder’s black rooster.

As we know, Splash is homozygous Blue. Here is the cross in Punnet Square form:
Image

As you can see, the expected outcome is 100% Bl/bl+, so all blue offspring.

However, the breeder in question got quite a surprise when her initial small hatch of eggs all from this cross resulted in:
* two black birds
* two white birds with black spots
* one blue bird.
They were understandably confused.

If we look at this as a logic problem, we can say that, based on the Punnet Square above, “If this bird is Splash, then when mated with a Black rooster, all the offspring will be blue.” The cross having been performed, we then look at the resulting offspring. Based on the variable colouring of the chicks we reach the following conclusion: “Not all of the offspring are blue, ergo this bird is not Splash.”

So if this hen is not Splash, what is she?

Here’s where we talk again about genotype and phenotype. The genotype is the genes that the bird carries, the phenotype is what they look like. Don’t be confused into thinking ‘but the bird has a Splash phenotype, so it must be Splash!’. The bird’s phenotype is ‘white with black spots’. Now we know of two genes that will produce this phenotype; the Blue gene when present in two doses, and the Dominant White gene. There are in fact three genotypes that will produce this phenotype. They are:
Bl/Bl Homozygous Blue (Splash)
I/I Homozygous Dominant White
I/i+ Heterozygous Dominant White.

Lets entertain the possibility that the hen’s phenotype is produced instead by Dominant White. If so she could have either one copy (heterozygous) or two copies (homozygous). Lets have a look at the relevant Punnet Squares.

Image
100% I/i+ = 100% Dominant White.
So, “If this bird is Homozygous Dominant White, when crossed to a black bird, all the offspring will be white with black spots”.

Image
50% I/i+ = 50% Dominant White
50% i+/i+ = 50% Black
Or “If this bird is Heterozygous Dominant White, when crossed to a black bird, half the offspring will be black and half will be white with black spots”.

Now lets look at the results of the cross again. The breeder reported that there were two black chicks, one blue chick and two white spotty chicks. For the bird to be Homozygous Dominant White all the chicks produced must be white, therefore the bird is not Homozygous Dominant White. However the Heterozygous cross produces half white and half black chicks, and looks like a very real possibility. So lets tentatively say that the bird in question is I/i+.

But what about the blue chick? One would assume that the breeder would have bought the bird in question from a line that contained blue. We also know that white can hide other colours underneath. However we know from the production of the black chicks and our first punnet square that the hen is definitely not Splash. But perhaps they could have one copy of Blue?

Image
50% Bl/bl+ = 50% Blue
50% bl+/bl+ = 50% Black
As we can see here, a blue bird crossed to a black bird will give half and half blue and black chicks. So it’s not unreasonable to assume that the hen in question is hiding one dose of blue under the single dose of Dominant White.

Now, because colour genes interact, we really want to look at the probabilities of two genes together. This is where we need to go the next level up with the Punnet Square.
First we array the mum’s Dominant White genes, then we do her blue genes. This way we can predict each possible combination that she can pass on. So she could pass on an I or an i+, and she could pass on a Bl or a bl+. This means that she has four possible combinations that she can pass on, because these genes 'segregate' (sort into the egg cell) randomly. These combinations are: I and Bl, I and bl+, i+ and BL, i+ and bl+.
Then we add Dad and do the same. He can only pass on i+ and bl+.
Image

Scarey huh? In health care this is usually where people wimp out and pay people like me to do this for them; I am grateful as it gives me a job. However in this case it’s actually not that hard. The Black rooster’s genotype is i+/i+, bl+/bl+ so he only has one combination of genes to pass on. Thus we can simplify the Punnet square like so:
Image

Filled out it looks like this:
Image

This gives us the following ratios:
25% I/i+, Bl/bl+ = 25% Dominant White (carrying blue)
25% I/i+, bl+/bl+ = 25 Dominant White
25% i+/i+, Bl/bl+ = 25% Blue
25% i+/i+, bl+/bl+ = 25% Black

So phenotypically we would see:
50% White with black spots
25% Blue
25% Black

And this is pretty close to what the breeder got, bearing in mind that 5 chicks is a very small sample size. A couple more clutches should fill out the ratios more evenly. Assuming that the breeder continues to get chicks in approximately these ratios, the conundrum is solved; the hen has one dose of Dominant White and one dose of Blue, and her genotype is I/i+, Bl/bl+.

It still took several of us nutting this through over a few days to work it out. :)

_________________
Brindabella Pekins


Top
 Profile  
 
PostPosted: Fri Jan 23, 2015 3:08 pm 
Offline
Deluxe Drake
Deluxe Drake

Joined: Fri Aug 08, 2008 9:31 pm
Posts: 2452
Location: Canberra
E Base Colours

Lets revisit the concept of the E base colour series for a moment, because they are very important when you are breeding birds. The E gene is the gene whose alleles determine the base colour pattern of the bird; all other genes then modify this pattern. Some genes work differently on different E bases. In order to have an understanding of the genetics of a bird's colour, you need to understand the base on which it is built.

There have been many E alleles hypothesised over the years. Some have not withstood the test of time (buttercup), proved to be the same as another already known allele ('recessive' wheaten) or proven to be so obscure they're found in only one or two breeds. This leaves us with five major alleles which I mentioned earlier, and I shall go into more detail here.

E - Extended Black

Extended Black builds a very dark bird. They regularly have dark legs and a dark beak, may be gypsy-faced, and are nearly all black.

Here is an Extended Black rooster. Note the legs and the 'crow wing' - the flights of his wing are black. The hen has a gold hackle on an otherwise black body; these birds are usually referred to as 'red brown'.
ImageImage

The chicks look like little penguins:
Image

When most people hear 'Extended Black' they think of black birds like these, because it only takes a few 'blackening' genes to render them pure black. Interestingly, the exact nature of these genes is still under debate.
Image

If you have a black line and you either cross out or otherwise lose some of these blackening genes, you start to see this sort of thing happening:
Image

Extended Black is an excellent base for making a really black bird, and subsequently for breeding blues and splashes on as it gives great depth of colour. I understand however that you cannot breed patterned birds on it, as the patterning gene will not work on Extended Black.

It should be noted that this is not the only base on which you can make a black bird.

_________________
Brindabella Pekins


Last edited by shairlyn on Sun Jul 19, 2015 1:51 pm, edited 1 time in total.

Top
 Profile  
 
PostPosted: Fri Jan 23, 2015 3:22 pm 
Offline
Deluxe Drake
Deluxe Drake

Joined: Fri Aug 08, 2008 9:31 pm
Posts: 2452
Location: Canberra
ER - Birchen

Birchen birds are very similar in initial appearance to the Extended Black birds. They have black bodies and wing flights, a gold hackle and the rooster has a gold saddle, and they have dark legs. The important and obvious difference in a Birchen bird is the lacing on the breast feathers.

Here is a Japanese Bantam gold Birchen hen:
Image

The chicks are also little penguins.
Image

Funnily enough, this colour is also often called 'red brown' if the breast lacing is poorly defined, and 'gold birchen' if it is good. 'Birchen' is regularly used to refer to what is more correctly called 'Silver Birchen', that is a Birchen bird with the Sex-Linked Silver gene, which we haven't talked about yet. Here are a couple of good Silver Birchens, showing the lacing, and a trio:
ImageImageImage

You can build a black bird on a Birchen base just as you can on an Extended Black base, using the same genes. One might wonder then why we bother differentiating the two? The important difference is that the Pattern Gene Pg works on Birchen. I have read that it is the only base upon which the patterning reliably extends to the rooster's tail, but I've never bred for patterns so I can't confirm this.

The magnificent Silver Spangled Hamburg is built on a Birchen base.
Image

_________________
Brindabella Pekins


Top
 Profile  
 
PostPosted: Fri Jan 23, 2015 3:29 pm 
Offline
Deluxe Drake
Deluxe Drake

Joined: Fri Aug 08, 2008 9:31 pm
Posts: 2452
Location: Canberra
e+ - Wildtype/Duckwing

The colour of the Red Jungle Fowl, Wildtype is perhaps the most distinctive colour, and the one against which others are compared. The male has a black body, a gold hackle and saddle and gold wing flights. The female has a brown body made up of a gold base with black speckles, a reddish chest and a gold hackle. Take note of the hen's red chest and the rooster's red shoulder. This is due to a gene called Autosomal Red Ar+, which I will discuss later.
ImageImageImage

The chicks are the most adorable little things, with camophlaging racing stripes that run from their heads all the way down their little bodies.
Image

Wildtype is a popular colour in game breeds, and understandably so given how spectacularly showy it is.

_________________
Brindabella Pekins


Top
 Profile  
 
PostPosted: Fri Jan 23, 2015 3:35 pm 
Offline
Deluxe Drake
Deluxe Drake

Joined: Fri Aug 08, 2008 9:31 pm
Posts: 2452
Location: Canberra
eWh - Wheaten

My favourite colour, wheaten is an interesting one and very distinctive in the hen. Not so in the rooster, who looks just like the Wildtype rooster in colouring. The hen however has lost most of the black speckling on the body and instead the red or 'salmon' breast colour extends all over her body, with black on her tail feathers and wing flights.
Image
Image

Wheaten nuggets are your classic cartoon-yellow chicks.
Image

Note the pale leg colour. You cannot get black legs on a wheaten bird, your choices are white or yellow.

_________________
Brindabella Pekins


Last edited by shairlyn on Fri Jan 23, 2015 3:42 pm, edited 1 time in total.

Top
 Profile  
 
PostPosted: Fri Jan 23, 2015 3:40 pm 
Offline
Deluxe Drake
Deluxe Drake

Joined: Fri Aug 08, 2008 9:31 pm
Posts: 2452
Location: Canberra
eb - Brown/Partridge

Again with Brown, the rooster is no different to the Wildtype rooster, it's the hen who differs. She is still a lot like her Wildtype sister, but she lacks the red or salmon breast, having speckling all over her body and a darker hue to the gold background. She still has a black and gold hackle. This is the favourite base for people wanting to play with pattern genes, as such it is very difficult to find a picture of a Brown hen without patterning, and indeed most Partridge standards call for the patterning on the female.

Here's the cock and the hen. Note that the patterning on the hen's breast is the same as the rest of her body; that's why this base is preferred:
ImageImage

The chicks are adorably brown and also have striping on their back like the Wildtype chicks:
Image

_________________
Brindabella Pekins


Top
 Profile  
 
PostPosted: Sun Feb 15, 2015 12:52 pm 
Offline
Gallant Game
Gallant Game

Joined: Sat Aug 08, 2009 1:26 am
Posts: 429
Location: N.E. NSW, Australia
Thank you Shairlyn for this thread. It's a great idea.

Re. the following:
Shairlyn wrote:
Note the pale leg colour. You cannot get black legs on a wheaten bird, your choices are white or yellow.

See the following thread by Htul BYP: Dark legged wheatens - anybody have these?

Willow-legged Wheaten Modern Game bantam:
Image

Yes, a correlation was found by some genetics researchers that dermal leg pigment was diluted by the wheaten allele. But Smyth did clarify at one point that this was for eWh - Dominant Wheaten & not ey Recessive Wheaten. Plus there is the case also of mutiple alleles on the dermal melanin locus, & it might be that similar dermal melanin alleles to the wild-type (id+) are able to express on eWh? Leg colour genetics can be quite complex, many gene combinations & modifiers that can vary expression. And I know you want to keep this simple, so will leave it at that....


Top
 Profile  
 
PostPosted: Fri Feb 20, 2015 9:10 am 
Offline
Deluxe Drake
Deluxe Drake

Joined: Fri Aug 08, 2008 9:31 pm
Posts: 2452
Location: Canberra
Interesting to know Kazjaps! I've never seen a willow-legged wheaten before, always learning something new. :)

I will mention here that I am talking in general terms when describing these genes; I am not going into breed specifics because apart from Pekins I have no experience with them. This is intended to give people the genetic tools, I would then advise talking to experts in your particular breed and using the tools to understand what they're describing to you.

Breeding Flocks

One of the reasons that I wanted to re-visit the colour bases is because I wanted to talk about setting up breeding flocks.

If you want to breed just one colour then your breeding flock is easy, you simply make them all one colour. If you have lots of space and want to breed lots of colours, you can set up a pen for each colour. But if you're like me and a backyard breeder with limited pen space and still want to breed lots of colours, you can often do so as long as you set up your breeding flocks carefully.

Basically, you can breed multiple colours from one flock as long as the base colour is the same.

Here is my old Extended Black based flock:
Image
As you can see there are:
* Four Black hens: Ink, Soot, Black Forest Cake and Midnight (don't ask me which is which in the photo)
* One Splash hen: Puddle
* One (dark) Cuckoo rooster: The Colonel.

I started with The Colonel and a couple of black hens, adding more as I could source them. From previous discussions we know that Cuckoo is sex-linked, but the rooster passes it evenly to all his offspring; the hen always passes it to her son. So over the black hens I got 50% black and 50% cuckoo offspring in both sexes.

Then I decided that I wanted to breed blue as well. I had the opportunity to buy Puddle the Splash hen (whose name was Rain until she sat down) and as we know, Splash is homozygous Blue. So Puddle would pass on one copy of the blue gene to all her offspring. The Colonel has only the bl+, non-blueing version of the gene, so all the offspring would be Bl/bl+, blue. The Colonel also passes one copy of the Cuckoo or Sex Linked Barring gene B to half of his offspring. So 50% were blue, and 50% were blue cuckoo.

Blue Cuckoo is not a standard colour. If you want to create a new colour, the easiest way to get something that looks nice is to use birds of the same base colour.

Here are the chicks:
Image
As you can see they are all little penguins, on account of all being Extended Black E/E. The ones that look a little washed out, with grey penguin suits, are blues. The ones with the white dots on their heads are cuckoos. Note the chick in the top right who has both; a blue cuckoo.

Here are some black, blue and cuckoo offspring:
Image

And there were these two funny looking things.
Image
By virtue of exclusion, they must be the blue cuckoos. They looked like clouds to me, and were named Snow and Storm.

Here's Snow when he grew up, and Storm at a slightly younger age:
ImageImage

Unfortunately a lot of the offspring were cockerels that season, but I did breed a lovely little blue pullet whom I called Bluebell and added to the flock. Unfortunately I don't seem to have any pictures of her, but put with The Colonel, she would give:
25% black
25% blue
25% cuckoo
25% blue cuckoo

So as you can see, I was getting four colours from one flock. Could I have gotten more? Quite easily. The obvious one to add to this flock is Lavender, which is also produced on the same Extended Black base. Both the hens and the rooster would need to at least carry it. So I would buy either a lavender hen or some black hens that were carrying (split for) lavender, and change The Colonel for a rooster who was either Lavender Cuckoo or Cuckoo carrying lavender. Then the flock would have produced six colours:
Black, blue, cuckoo, blue cuckoo, lavender, lavender cuckoo.

You could also potentially add recessive white if you could find appropriate birds.

As long as you stick to the same base, the colours will often work together. But you need to have an understanding of the genes that cause the colours you're using, and use your punnet squares to predict the resulting offspring before you buy the parents.

_________________
Brindabella Pekins


Top
 Profile  
 
PostPosted: Tue Feb 24, 2015 2:34 pm 
Offline
Deluxe Drake
Deluxe Drake

Joined: Fri Aug 08, 2008 9:31 pm
Posts: 2452
Location: Canberra
Marek’s Resistance

I’m going to step away from the genetics of colour for a moment and talk about Mareks Disease. What I specifically want to talk about is Marek’s Resistance. It is real, it exists, and it is genetic. It can be selected for in a flock, and it can be lost from a flock. You see those beautiful birds of mine in the previous post? My gorgeous blue/black/cuckoo flock that I sourced from award-winning breeders at not inconsiderable expense, nurtured and bred and loved and even won a few prizes with myself? With the exception of Black Forest Cake, every since one of those birds is dead. None of them lived past the age of three, and most of them died younger. Most of them died of Mareks.

When I started breeding chooks I knew almost nothing about Mareks, it was vaguely on the radar as ‘a disease chooks get’ which I’d heard of on BYP. As my flock started dying of it I did some research. Here’s what I learned.

So what is Mareks? The Mareks virus is a herpes virus similar to that which causes cold sores in humans, but in chickens it causes tumours of various cell lines, causing paralysis, tumours on the organs and suppression of the immune system. It should not be confused with avian leukosis, which different. It is extremely common in Australia, and difficult to guard against. BYP has an excellent, comprehensive thread on Mareks here. It largely comes in three forms: Paralysis, Lymphomatous and Immunosuppression. I saw all three in my birds.

What makes Mareks so difficult is the fact that the virus is so common, and the fact that there is no treatment, and no cure. There is only prevention. There are two main methods of prevention: breed for Mareks Resistance, or Vaccinate.

The vaccine comes in 1000 dose vials, and once opened it must be used or thrown away. Chicks must be vaccinated when they hatch, and because the virus is shed in feather dander they must be reared away from adult birds and have no contact for the first three weeks of their lives. What this means is that large-scale breeders tend to vaccinate, because they have the number of birds and appropriate set-up to facilitate it, and small back-yard breeders tend not to, because they don’t.

What’s the alternative to using a vaccine? Breeding for resistance. There is a gene dubbed ‘B21’ that is dominant and confers Mareks resistance on a bird. You select for it by not vaccinating for generations and breeding with the birds who don’t get Mareks. On the other hand if you vaccinate then the birds who are not resistant don’t die, and you can lose the resistant genes simply because you’re not selecting for them. You therefore create a strain that is vaccine dependant.

There are plenty of discussions/arguments over which is the ‘correct’ approach to take, and I’m not looking to get into them here. I will say up front that I am in favour of breeding for resistance, because I can’t afford to vaccinate and I hen-rear my chicks in small batches. There is nothing cuter than a walking tea-cosy with her skirts full of fuzzy nuggets. However I can fully see why for many, vaccination is the way to go. I do know of a consortium of backyard breeders in my area who get together to vaccinate, because as a larger group they can afford and share out the vaccine.

What I think is important is that, as a breeder, you decide early on whether or not you are going to vaccinate, and with that in mind, select your breeding stock intelligently. If you do not plan to vaccinate then you may wish to avoid obtaining stock from vaccinated lines, because although the vaccinated parent birds will be fine, their offspring are likely to be very susceptible to the disease. Resistance is dominant however, so if a breeder really wanted some birds from a vaccinated line but did not want to vaccinate their own birds, they could obtain pullets from that line and a cockerel from a resistant line, or vice versa, and at least half the offspring should be resistant. Anything is better than losing your beloved birds.

As a beginner breeder who had just lost one entire flock I was absolutely devastated. I had just started producing gorgeous young birds from that flock and even won a few prizes with them. I was desperately considering contacting people to whom I had sold birds to see whether I could buy some offspring in an effort to re-establish the bloodlines. I was sitting in the backyard watching my remaining birds, when the penny dropped. Whilst the black/blue/cuckoo flock had been in the process of imploding, the wheaten flock had just gone on its merry way, my little fluffies poddling around doing their thing, and not one case of Mareks. I am going to tempt fate by saying that, to this day, none of my wheatens (or the resulting lavender wheatens) have died of Mareks.

When I obtained The Colonel, my magnificent cuckoo rooster, I also obtained a fabulous pullet-breeding wheaten fellow, from the same breeder. He was named The Major. Both birds were from vaccinated lines. The difference was their hens. The Colonel’s black hens were from similar show lines, all vaccinated, and I believe that Puddle’s parents were vaccinated. She herself was not, she died of Mareks. However wheaten hens are much harder to source as it’s not a popular colour. They came one at a time from all sorts of different places, many of them small breeders like myself, and presumably from unvaccinated lines. Whether The Major himself was resistant I will never know, but I’m sure his girls were, and their descendants continue to be.

So, the salient points:
* Mareks is a virus with no cure and a high mortality rate amongst poultry. It is transmitted from bird to bird through feather dander.
* It can be prevented by vaccination or breeding for resistance.
* The Mareks vaccine must be given to day old chicks and they must be brooder reared away from other birds. No hen-rearing.
* There is a gene B21 which makes birds resistant to Mareks. You can breed for it like any other gene.
* Vaccinating preserves Mareks succeptibility.
* If you want to breed, decide whether you want to vaccinate or breed for resistance.
* If you are not going to vaccinate, try to source birds from resistant lines.

_________________
Brindabella Pekins


Top
 Profile  
 
PostPosted: Wed Feb 25, 2015 8:42 am 
Offline
Great Game
Great Game

Joined: Fri May 19, 2006 11:57 am
Posts: 1267
Location: Hamilton Vic
Whilst the B21 haplotype of the MHC gene does confer resistance it is not complete resistance and the virus itself has evolved over the years such that we have seen an increased pathogenicity of the Mareks Disease Virus and it is thought that this increased pathogenicity occurs in both resistant and non-resistant host lines. Breeding for and fixing a dominant gene in a population in the absence of test crossing and pedigree management is not straight forward when heterozygous individuals are hard to identify and indeed if the flock is exposed to less virulent forms of Mareks then it is quite possible that 'resistant' phenotypes will in fact be 'escapes' leading to incorrect scoring of resistance and susceptibility in progeny generations. Breeding for resistance is a noble aim but I think a cautionary note is in order to say that it is not as straight forward as having the B21 haplotype and away you go. This variant has been known since at least the late '70s so if it were that simple there would be no Mareks left in commercial flocks. Having said that in breeds we have that are notorious for their susceptibility then bringing the B21 haplotype into these breeds would be of great benefit to their fitness.


Top
 Profile  
 
PostPosted: Thu Mar 19, 2015 1:05 pm 
Offline
Gallant Game
Gallant Game
User avatar

Joined: Thu Jun 17, 2010 4:25 pm
Posts: 501
Location: Eldorado:Vic
All i can say is WOW , i am going to have to read this several time to digest lol

_________________
Owner of 20 chickens , 20 cows , 7 peafowl , 4 pigs , 1 horse and 1 cat


Top
 Profile  
 
PostPosted: Sun Jul 19, 2015 11:12 am 
Offline
Deluxe Drake
Deluxe Drake

Joined: Fri Aug 08, 2008 9:31 pm
Posts: 2452
Location: Canberra
Apologies for falling off the face of the earth, life's been very busy lately but I am still alive and have several more genetics lessons planned out in my head. I just need to type them up!

I've had requests for gold-affecting genes and I definitely want to get onto those, but I've covered all but one of the major black-affecting genes, so I figure I might as well round out the set before getting into gold. Remember that I'm only talking about genes that are commonly found across most breeds, I'm not getting into breed-specific factors because I just don't know enough about them. I'd always encourage you to talk to your local breeders. :)

Things we've talked about so far:

Colour Bases
Extended Black (E)
Birchen (ER)
Wild Type (e+)
Wheaten (eWh)
Brown (eb)

Affecting all colour
Colour Removing: Recessive white (c)
Colour Restricting: Cuckoo or Sex-Linked Barred (B)
Colour Diluting: Lavender (lav)

Affecting Black
Black Removing: Dominant White (I)
Black Restricting: Columbian (Co), Dark Brown (Db)
Black Diluting: Blue (Bl), Dun (I^d), Smokey (I^s)

There are actually two major black-affecting genes that I haven't talked about. One is the Pattern Gene. However as this gene has quite a complex relationship with other black-affecting genes, I want to give it it's own section. So the last remaining gene is:

Black Extending: Melanotic

Melanotic is a partially dominant gene, given the shorthand 'Ml'. It extends the expression of black over the body, and is particularly noticeable in the hen where it will extend the black pigment over her back. The effect is less obvious in the cock.

It is classically one of the genes that turn an Extended Black based red-brown into a true black.

Extended Black on it's own (E, red-brown colour):
Image

A fully black bird (E, Ml):
Image

It can turn a Wheaten bird (eWh):
ImageImage

Into a Furnace (eWh, Ml):
ImageImage

It can turn a Buff Columbian (e+, Co):
Image

Into a Quail such as in the Belgian breeds (e+, Co, Ml):
ImageImage

Note how dark the backs of the Furnace and Quail hens are.

_________________
Brindabella Pekins


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 35 posts ]  Go to page Previous  1, 2, 3  Next

All times are UTC + 10 hours [ DST ]


Who is online

Users browsing this forum: Google [Bot] and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB® Forum Software © phpBB Group
©2004-2014 Backyardpoultry.com. Content rights reserved
freestone