i had never heard before there were other phenotypes associated with monkey mouth, ie leg issue. it seems to me that the defect is something to do with cell spacing being constricted somehow, ie, if the head doesn't elongate, the shoulder doesn't fully cover what it should constricting it's eventual movement and the spasitc thing is starting to make sense. this is classic descriptions of a cascade of gene expression. this leads me to believe that the expression, more recessive, in intent is accurate, but not accurate in that the reason it is more recessive is that there is probably more than one gene involved.
see this paper for a boring discussion of how genes work
http://www.genome.org/cgi/content/full/GR-2096Rv1
right now, we are finishing up sequencing at least one representative of most of the genes in human, frog, zebrafish rat, mouse. there are many what are called alternative splice forms of these genes either because they have a single nucleotide polymorphism (a change in base from C to T, called a snp for short), and that the protein truncates early like in PHA, I don't remember about TH. when i was at a previous company, for some genes, we found 15 to 15 alternative splice forms for EACH gene. some were garbage and were in the middle of being transcribed, which is the source of mRNA used to create cDNA libraries, but some of these alternatives can be regulated by promoters, either upstream or downstream, or on another chromosome, ie epigenetics, all kinds of things. geneticists like to call the single gene traits the low hanging fruit, ie easy to get. it's the multiple gene defects, and or multiple copy defects like hunningtons disease, which was found on chromosome 19 in humans by one of the guys in our lab because he assembled it, someone figured it out, and wham, a discovery! monkey mouth is probably not like that, but probably either multigenic. whether a trait is a single gene determines if researchers will go after them, because it's relatively straightforward to do it. there really isn't a track record of success for the multigenic or expression based defects. this is why genomics is changing and the community is looking at the perspective called the transcripome instead of the genome. just like any log leap in understanding, there will be pitfalls, low hanging fruit etc. what drives biology is new ways to screen or seive what you are looking for. an alternative to that is smart screening, like in the pharma industry, where there are literally thousands of slightly modified compounds, and most of them have been tested, but now that we can look at differences in genomes between individuals, more and more medicines are going to be tailored for a transcriptome. the easiest way to think of this is viagra. you proably heard the other day that people can have rapid onset of deafness (not blindness) from using viagra. well, those people probably have some little thing that is incompatible, but the vast majority of the population will continue to enjoy the product. perhaps they will even make a test to see if you are compatible. also think of the commercials where they say a simple blood test is necessary before your doctor can prescribe so and so. this is why pharma is so expensive. can't wait for hillary care.
so if monkey mouth is multigenic, lets just say for comparison, it's like the tenderness genes. you need all 6 to have a 2.2 lb less force necessary to pierce steak with relatively blunt "knife".
the more "stars" you remove, the more "recessive" the effect. probably there are some combo's where you have 1 or more stars and the phenotype is gone. so one day it could come down to , so and so bull only has 2 of the monkey mouth stars, and needs 4 to start manifesting, so only breed to cows with so many "stars" or in this case i guess you could call them black holes.
savvy?