Author Topic: Muffs and Beard (Mb)  (Read 2855 times)

Lindsay Helton

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Muffs and Beard (Mb)
« on: October 28, 2019, 11:49:49 PM »
The American Poultry Association standard of perfection for an Ameraucana states that the face should be "nearly hidden by muffs" and that muffs and beard should be "full, well-rounded, medium length, forming three separate lobes." The absence of muffs and beard is a disqualification.

Muffs and beard (Mb) is known as an autosomal incomplete dominant trait. It is an observable physical characteristic involving elongated feathers that form on the side of the face and below the beak.

First, let’s break things down and explore the meaning of an autosomal incomplete dominant trait.

Chickens have 39 pairs of chromosomes. They have two categories of chromosomes known as sex chromosomes and autosomes. An autosome is simply defined as a chromosome that is not a sex chromosome. Genes are contained within these chromosomes. Each parent contributes one allele to form a particular gene in a diploid organism. Incomplete dominance means that one allele is not completely expressed over the allele that it is paired with. This results in a phenotype that is a combination of the phenotypes of both alleles.
 
There are three genotypes for the Mb locus regulating the Mb trait:
 
1) Mb/Mb homozygous (carrying two copies of the gene and exhibiting a full muff/beard)
 
2) Mb/mb heterozygous (carrying one copy of the gene and exhibiting a partial muff and beard)
 
3) mb/mb wild-type homozygous (not carrying any copies of the gene and what many refer to as clean-faced)

So how does the muffs and beard (Mb) trait affect our Ameraucana breeding programs? Using a punnett square, we can predict the genotypes of a particular cross. 

If you mate two homozygous Mb/Mb birds together, all resulting offspring will have two copies of the Mb gene and full muffs and beard.

If you mate two Mb/mb heterozygous birds together, 25% of the offspring will be homozygous Mb/Mb and have full muffs and beard, 50% will be heterozygous Mb/mb and have partial muffs and beard, and 25% will be homozygous wild-type mb/mb and not have muffs or a beard.

If you mate a Mb/Mb homozygous bird with a Mb/mb heterozygous bird, 50% of the offspring will have full muffs and beard and 50% will have partial muffs and beard.

Mb birds are born with muffs and beard, and the remarkable differences of Mb/Mb, Mb/mb, and mb/mb birds can be witnessed during embryonic development.  I have attached a photo from a study that shows HOXB8 expression is increased considerably in the facial skin of developing Mb/Mb embryos and postnatal chicks (Guo et al., 2016).

This study also found that the Mb allele that causes the Mb phenotype is “a derived allele where a complex structural variation (SV) on GGA27 leads to an altered expression of the gene HOXB8. It is a structural mutation resulting from the duplication of three regions on chicken chromosome 27 (GGA27). The three duplication regions are located around 1.70 Mb (CNV1), 3.58 Mb (CNV2), and 4.47 Mb (CNV3) on GGA27, respectively (Guo et al., 2016).”

lt is important to note that several studies have identified that wattles are absent or small when Mb is present (RG, S 1990). The American Poultry Association standard of perfection for an Ameraucana states that wattles should be “very small and preferably absent.” Many researchers speculate that the Mb trait is highly associated with the Wattles locus and that there are underlying complex interactions between Mb and Wattles.

Hopefully this post will help you as you are assessing your Ameraucana chicks and breeding age birds for the Mb phenotype and setting up breeding pens. Good luck with your flock!

A special thank you to the APA for granting me permission to use portions of the standard when answering breeding questions and creating educational posts.

To purchase an American Poultry Association standard of perfection book, visit the following link:

http://www.amerpoultryassn.com/store.htm

Guo Y, Gu X, Sheng Z, Wang Y, Luo C, Liu R, et al. (2016) A Complex Structural Variation on Chromosome 27 Leads to the Ectopic Expression of HOXB8 and the Muffs and Beard Phenotype in Chickens. PLoS Genet 12(6): e1006071.

RG S (1990) Mutations and major variants of plumage and skin in chickens. In: Crawford RD, editor Poultry Breeding and Genetics Amsterdam, Netherlands: Elsevier: 169–208.
« Last Edit: December 30, 2019, 01:33:36 AM by Lindsay Helton »
“If we live by the Spirit, let us also keep in step with the Spirit.” Galatians 5:25

Lindsay Helton

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Re: Muffs and Beard (Mb)
« Reply #1 on: October 05, 2021, 06:16:47 PM »
Someone asked me the other day if I had an example photo of the difference in Mb/Mb homozygous (carrying two copies of the gene and exhibiting a full muff/beard) and Mb/mb heterozygous birds. Here you go!

Keep in mind that Mb is an autosomal incomplete dominant trait, so you may see some variance in the expression of Mb/mb heterozygous birds. I also think the overall appearance of Mb can be affected somewhat by the feathering of the particular bird. An Ameraucana is neither a hard nor soft-feathered bird. Ameraucana that are too soft-feathered will often lack the desired definition of three separate lobes that we should strive for. 

If you are curious about examples of hard-feathered and soft-feathered breeds, Modern Games and Cornish are two examples of hard-feathered breeds. Orpington and Cochin are two examples of soft-feathered breeds. An Ameraucana is a bird of moderation, including feathering.

Or, even take a look at the standard for the Faverolle breed, which is soft-feathered. The description for the muffs and beard of a Faverolle states the beard should be elongated, muffs full, feathers projecting from face, extending to and covering ear-lobes.

It’s neat to think about the differences in the standard writing of different breeds with traits in common, and why the verbiage is different.

However, one element of the standard that comes to my mind and is worth mentioning is in relation to the body and stern. For the Ameraucana male, the stern should be well-tucked up. For the Ameraucana female, the body and stern should be full but trim, fluff well-tucked up.
« Last Edit: October 06, 2021, 10:06:42 AM by Lindsay Helton »
“If we live by the Spirit, let us also keep in step with the Spirit.” Galatians 5:25

kkdossey

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Re: Muffs and Beard (Mb)
« Reply #2 on: October 06, 2021, 07:17:13 AM »
Thank you for the info.
Some of my birds tend to keep their partners muffs picked pretty well off and I may have some heteros in there.  I've got to make sure I know for sure they're homo before I use them.  I need to separate them and let them grow back I guess.
Kris Dossey

Lindsay Helton

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Re: Muffs and Beard (Mb)
« Reply #3 on: October 06, 2021, 10:09:10 AM »
Some of the pullets in my pullet pens are misbehaving and preening each other’s beards. Unfortunately I can’t single stall them for conditioning because white bantam are taking up those pens.
“If we live by the Spirit, let us also keep in step with the Spirit.” Galatians 5:25