[Menzie]

about breeding, so I put it here.

OK, these are things I think about when I wake up and can't go back to sleep (note it's 5 a.m......).

I read in the Basset Hound magazine (put out by Dog Fancy) where Claudia Orlandi said that good shoulder assemblies are recessive int he basset, and therefore really difficult to breed for. That comment stuck with me... now keep in mind, my knowledge of genetics, as a non-breeder, is limited to some fuzzy high-school memories of Mendel's peas and blue eyes vs. brown.. but here's what I was thinking...

Let's say you breed two dogs who have the recessive for good shoulder assemblies, and you get the exact 1-in-4 "expression" of that recessive. So Pup A has a good shoulder assembly, and the other three don't.

1. If all four pups were girls, and you bred them all to the same stud (who carries the recessive for good shoulders), does Pup A have a greater chance of having pups with good shoulder assemblies? Or do they all have the same chance?

2. If you have a pup with a not-good shoulder assembly, but they have a mother, or grandfather, with good shoulders, do you know for sure that they then carry the recessive? In other words, how many generations down will carry that recessive, if you have someone in the pedigree who had good shoulders? OR does it depend on who else is in the lineage (and whether they carried the recessive)? Or is the recessive gene, once there (as evidenced by good shoulders somewhere in the pedigree) always present in all future pups?

See the things I think about when I can't sleep.... :roll:

 

[biscuit]

1. If all four pups were girls, and you bred them all to the same stud (who carries the recessive for good shoulders), does Pup A have a greater chance of having pups with good shoulder assemblies? Or do they all have the same chance?

It depends on whether they are all carrying the recessive. If they are all carrying the recessive, then chances of the recessive trait showing up are equal.

Which is the thing with recessives. Phenotype vs. genotype, all that. Just because a trait doesn't show up in the phenotype doesn't mean it isn't in the genotype.

Meaning it is perfectly possible to carry a recessive trait, but not have that trait express itself. Which is why, several generations down the line, poof, a recessive trait can show up even though no one *knew* they were carrying that trait because their parents and grandparents and ggrandparents didn't have it.

2. If you have a pup with a not-good shoulder assembly, but they have a mother, or grandfather, with good shoulders, do you know for sure that they then carry the recessive?

Maybe. Maybe not. This is where genetic testing comes into play. Think of humans. If certain diseases are in your background (sickle cell anemia, Huntington's), chances of you acquiring that disease skyrocket in comparison to the general population. But they have ways these days of checking to see if you carry those genetics. But they don't have genetic tests for everything at this time.

In addition, for some recessive traits, there are *degrees* of expression, so to speak, which may or may not be entirely genetic. My niece has a genetic disorder in which her kidneys cannot process the aminos from protein, for example. There are essentially four stages of this disorder. Whether these stages represent difference genetic configurations or interfaces between genetics and physiology or what seems to be kind of up in the air.

In other words, how many generations down will carry that recessive, if you have someone in the pedigree who had good shoulders? OR does it depend on who else is in the lineage (and whether they carried the recessive)? Or is the recessive gene, once there (as evidenced by good shoulders somewhere in the pedigree) always present in all future pups?

See the things I think about when I can't sleep.... :roll: [/QB]

The recessive trait can be carried forever and ever and ever. Back to humans again ... I'm rh negative. We're a minority because rh negative blood is a recessive trait. Yet we persist at (I think) 5% of the population because the genetics for rh negative are so widely distributed in the general population.

Just because both parents do not arry the trait does not mean that trait is not passed on. It only means that trait is not expressed unless both parents carry it.

 

[Betsy Iole]

Not sure whether the question is about shoulder layback or about inheritance of simple autosomal recessive traits? Although good shoulder layback is hard to get and hard to keep, it would be surprising if a simple autosomal recessive gene were responsible for everything that goes into it.

If the question is about inheritance of simple autosomal recessive traits, a straightforward discussion of their inheritance can be found here. In this discussion, "carrier"=1 copy of the recessive gene and "affected"=2 copies of the recessive gene.

 

[Menzie]

Thanks, Betsy. That was a good description of how recessives are carried... I guess my question was about recessives in general.. it was just the comment about shoulder assemblies that started me thinking about it. (I'm sure, that there must be more to good shoulders than just one recessive gene - if that was all there was to it,someone would probably have figured out how to breed for it consistently by now! )

 

[Barbara Winters]

As Betsy says it's unlikely that one gene were responsible. Most likely there are multiple genes involved in producing "perfect shoulder layback." Check out the chart in this article which predicts the number of genotypes from the number of genes:
Genetic and Environmental Effects on Quantitative Traits

As I found when I took genetics in college things get a little more complicated than Mendel's smooth and wrinkled peas. Here's a great discussion of genetics in a bit more detail: Basic Genetic Concepts

[ March 19, 2004, 06:05 PM: Message edited by: Barbara Winters ]