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#116947 - 12/09/17 03:07 PM Bantam dwarfing
Simon V. Offline
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Registered: 04/16/05
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Loc: Australia
I was hoping someone could check my understanding on inheritance of bantam dwarfing.

My reading so far indicates there are several different genes responsible for dwarfing. Would I be right to assume that in most common bantam breeds (specifically interested in Pekins) dw is the one we are going to find most often and this is a sex-linked gene that behaves in an incompletely dominant way resulting in intermediate expression when heterozygous (in males)?


Edited by Simon V. (12/09/17 03:08 PM)

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#116950 - 12/10/17 03:18 PM Re: Bantam dwarfing [Re: Wieslaw]
KazJaps Offline
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Loc: Australia
The following old research, mostly from Poultry Breeding & Genetics:
http://www.edelras.nl/chickengenetics/mutations2.html#gen_mut_dwarf
Dwarfing Genes:

There have been four loci identified with dwarfing mutations, one locus with multiple mutation alleles:
  • Z
  • rg
  • adw
  • dw, dwM, dwB

* Z "Dominant Sex-linked Dwarfism"– found in Golden Sebrights (Maw 1935, crossed Light Brahma with Gold Sebrights).

* rg "Recessive Sex-linked Dwarfism"– Black Rosecomb Bantams (Godfrey 1953, crossed Barred Plymouth Rock with Black Rosecomb bantams)

* adw "Autosomal Dwarfism"- mutation occurred in Cornell K strain White Leghorns (Cole 1973)

* dw, dwM, dwB "Sex-linked Dwarfism"- closely linked to silver-gold & slow-rapid feathering loci.

-------------------------

- dw Mutation appeared in a New Hampshire flock (Hutt 1959)

- dwB found in Golden Sebright (Custodio & Jaap 1973) (dwB dominant over dw)

dwM found in a meat-type line (Hsu et al 1975). (inheritance relationship with other locus alleles not determined).

Generally large & bantam crosses produced F1 offspring intermediate in size (sometimes closer to bantam size). F2 offspring had the greatest variation in size. An exception was found in a study by Danforth (1929). There was variation between bantam breeds when he crossed a Millefleur Belgian d'Uccle Bantam male with Sebright females. Some F1 progeny were larger than the parents, & in later generations birds both larger and smaller than the parental types were obtained.

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#116951 - 12/10/17 03:49 PM Re: Bantam dwarfing [Re: KazJaps]
KazJaps Offline
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Registered: 08/30/02
Posts: 2819
Loc: Australia
In this old thread, a story about an Australian poultry breeder Bill Stanhope who developed commercial bantam layer strains from crosses to bantam breeds (not commercial sex-linked dwarfism strains, different genetics):
http://www.the-coop.org/forums/ubbthreads.php?ubb=showflat&Number=21416

The original story on Australian TV:
http://www.abc.net.au/tv/programs/landline/old-site/content/2006/s1614479.htm

The problem with sex-linked dwarf genes was that egg size is decreased as well. Bill Stanhope used bantam genes where small hens laid commercial egg sizes.

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#116952 - 12/10/17 04:15 PM Re: Bantam dwarfing [Re: KazJaps]
KazJaps Offline
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Registered: 08/30/02
Posts: 2819
Loc: Australia
The following post on genes that increase size (which needs to be taken into consideration when crossing bantam breeds to fowl larger than Red Junglefowl).
http://www.the-coop.org/forums/ubbthreads.php?ubb=showflat&Number=93336#Post93336
* Also note Kaalnek's results from crossing Sebrights with large fowl, different results depending on which gender is the bantam.

--------------------------
To mutations that increase size - ie larger than Red Jungle Fowl.

The twofold difference in adult size between the red junglefowl and White Leghorn chickens is largely explained by a limited number of QTLs. Anim Genet. 2003 Aug;34(4):264-74. -Abstract here
Quote:
The QTL analysis of growth traits revealed 13 loci that showed genome-wide significance. The four major growth QTLs explained 50 and 80% of the difference in adult body weight between the founder populations for females and males, respectively. A major QTL for growth, located on chromosome 1 appears to have pleiotropic effects on feed consumption, egg production and behaviour. There was a strong positive correlation between adult body weight and average egg weight. However, three QTLs affecting average egg weight but not body weight were identified. An interesting observation was that the estimated effects for the four major growth QTLs all indicated a codominant inheritance.


In summary:
* 13 loci affected growth (in these White Leghorns)
* 4 of which affected major growth, 50% in females, 80% in males.
* Of these 4 loci, all indicated codominant inheritance.

----------------------------

Further research 2009:
Genetic analysis of an F2 intercross between two chicken lines divergently selected for body-weight. BMC Genomics. 2009; 10: 248. Full report
This time they refined the research, & included epistatic interactions. Eg, apparently chromosome 7, 'Growth9' QTL is important for expression for other growth loci alleles (including on other autosomal chromosomes).
Quote:
Nine of the 15 unique epistatic pairs involved interaction with the major QTL on chromosome 7 (Growth9)....

....Originally, six genome-wide significant interacting loci were reported on chromosomes 1, 2, 3, 4, 7 and 20. The loci on chromosome 1, 4, 7 and 20 are still genome-wide significant in this analysis, though the loci detected on chromosome 2 and 3 are no longer significant using the new map. On the other hand, two new loci located in a previously uncovered part of chromosome 3 as well as a locus on chromosome 24 now reach significance above the threshold level.



In short - growth factors / body weight is a polygenic trait.

- Growth factor loci were found on chromosomes 1, 2, 3, 4, 7, 20 and 24.

- 15 loci (inc. two new ones) were found to influence growth.

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#116954 - 12/10/17 06:19 PM Re: Bantam dwarfing [Re: KazJaps]
KazJaps Offline
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Registered: 08/30/02
Posts: 2819
Loc: Australia
In the following discussion paper, it's noted that 3 different sex-linked dwarfism genes in 4 commercial lines have been determined through DNA sequencing:
TIXIER-BOICHARD, M. (2002). From phenotype to genotype: major genes in chickens. World's Poultry Science Journal, 58, 65-75.
http://prodinra.inra.fr/record/8065
Abstract

Table 1 Molecular defects of the growth hormone receptor gene and body weight reduction in sex-linked
dwarf chickens.

- Substitution (TÆC) in GA (USA) meat type line
- 1773 pb deletion in CT (USA) meat type & OB (France) layer brown egg lines
- Substitution (GÆT) in WL (France) layer white egg line

---------------------------
In the following 2017 paper they note the many different genes with mutations that can cause dwarfism in dometic animals:

Boegheim et al. 2017. Current insights into the molecular genetic basis of dwarfism in livestock.
Vet J. 2017 Jun;224:64-75. doi: 10.1016/j.tvjl.2017.05.014. Epub 2017 Jun 2.
Abstract: https://www.ncbi.nlm.nih.gov/pubmed/28697878
Quote:
Many forms of dwarfism are inherited and result from structural disruptions or disrupted signalling pathways. Hormonal disruptions are evident in Brooksville miniature Brahman cattle and Z-linked dwarfism in chickens, caused by mutations in GH1 and GHR. Furthermore, mutations in IHH are the underlying cause of creeper achondroplasia in chickens. Belgian blue cattle display proportionate dwarfism caused by a mutation in RNF11, while American Angus cattle dwarfism is caused by a mutation in PRKG2. Mutations in EVC2 are associated with dwarfism in Japanese brown cattle and Tyrolean grey cattle. Fleckvieh dwarfism is caused by mutations in the GON4L gene. Mutations in COL10A1 and COL2A1 cause dwarfism in pigs and Holstein cattle, both associated with structural disruptions, while several mutations in ACAN are associated with bulldog-type dwarfism in Dexter cattle and dwarfism in American miniature horses. In other equine breeds, such as Shetland ponies and Friesian horses, dwarfism is caused by mutations in SHOX and B4GALT7. In Texel sheep, chondrodysplasia is associated with a deletion in SLC13A1.

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#116955 - 12/11/17 03:18 AM Re: Bantam dwarfing [Re: KazJaps]
Simon V. Offline
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Registered: 04/16/05
Posts: 197
Loc: Australia
Ok, so it is most likely polygenic... I am specifically asking because I was recently told that no true bantam silkies exist in Australia (known bantam silkies might be a better thing to say) and I have been thinking about what would be needed to actually do it. I have crossed silkie hens with a Bantam Australorp (black) and got very small hens but the cockerels were all intermediate in size. This was for a different project (an all black, single black combed, black skinned bantam breed) and I think if I was to have a go at this I would use a Pekin to start with because of the leg feathering that already exists. I was also thinking there is probably heaps of bantam silkies out there given the use of lavender pekin in trying to create lavender silkies...


Edited by Simon V. (12/11/17 03:24 AM)

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#116956 - 12/11/17 03:28 AM Re: Bantam dwarfing [Re: Simon V.]
Simon V. Offline
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Registered: 04/16/05
Posts: 197
Loc: Australia
Do I need third-party image hosting to post photos on here?

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#116957 - 12/11/17 02:52 PM Re: Bantam dwarfing [Re: Simon V.]
Wieslaw Online   content
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Yes, but Photobucket is no longer an option, unless you'll pay 400 dollars a year.

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#116958 - 12/11/17 06:43 PM Re: Bantam dwarfing [Re: Simon V.]
KazJaps Offline
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Registered: 08/30/02
Posts: 2819
Loc: Australia
Originally Posted By: Simon V.
Do I need third-party image hosting to post photos on here?

Yes. The Coop doesn't have image hosting.
-------------------

They are tiny...

Australian Standard -Silkie Bantam weights:
BANTAMS:
Male 570 –680g (20 –24oz)
Female 455 –570g (16 –20oz)

* These weights are only slighter more than what I'm getting in my Modern Game Bantams wink

Australian Standard -Pekin Bantam weights:
Male = 910 – 1020g (32 – 36 oz)
Female = 790 – 910g ( 28 – 32 oz)

So the Pekins weigh way too much (also consider the trend of Australian Pekin exhibition lines being oversized as well, ie higher than above weights).

Australian Standard - Belgian d'Uccle weights (still too high):
Male 790 - 900g (28 - 32 oz)
Female 700 - 790g (25 - 28 oz)
- the British Poultry Standard has d'Uccle hens 24 - 28 oz, British Belgian club has 680 -790g hens. Got a faint memory that the Australian Standard d'Uccle hens were bumped up in recent years.

* Note too, many Australian d'Uccle lines can be oversized. But I used to have d'Uccle hens in the bantam Silkie weight range.

Whatever you use, I would weigh them before purchase smile

Yes, in recent years Australian breeders have been using Lavender Pekins in the development of Lavender Silkies, but pre-dating this silkied Lavender Araucanas had been popping up, & I know there was a developed Lavender Silkie line years before (eg early 2000's I'd seen advertised birds). First there were lav in Belgians, then plenty of crosses later, see the gene popping up in many breeds, (lavender Araucanas one of the first developed from d'Anver crosses, copying the lav Araucana variety developed in the UK).

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#116959 - 12/12/17 04:19 AM Re: Bantam dwarfing [Re: KazJaps]
Simon V. Offline
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Registered: 04/16/05
Posts: 197
Loc: Australia
Hmmm... how hard do you think it will be to breed the ruff out if a Belgian d'uccle was chosen to start with? I have been trying to find (just now.. so not an extensive search, yet), the inheritance pattern of it in d'uccles. Not sure I want to start with something in the mille fleur range, either, or have the dropped wings in there.


Edited by Simon V. (12/12/17 04:21 AM)

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