Tracy Bassett wrote:
<<I have always been told that the double dew claws are a simple recessiveOkay, if my genetics is right and the gene works in the following way, then this should be how it comes down:
gene trait. This would mean that both sire and dam would have to have the
gene.>> JoeIf this is the case, how is it that a mating between a bitch with double
dewclaws and a dog with singles, can produce pups with doubles as I saw
here? I'm getting confused!! :-/Tracy Bassett
Canberra, Australia
espinay@dynamite.com.au
Assume that double dews are dominate --> D
Single dews are recessive
--> d
Also assume that double dews are heterogenous - they can appear when
1 dominate and 1 recessive gene (Dd) are linked OR they can be homogenous
dominate - 2 dominate genes (DD) are linked.
Assume again that single dews are homogenous recessive- there must
be 2 recessive genes (dd) for the triat to show.
Each adult dog contributes 1 of his/her 2 dew genes to each new puppy.
Mendelson's punent square would show us the following outcome if both
parents each carried one dominate and one recessive gene (this means they
show the trait of double dews, but carry a gene that would
make it possible to have single dews in a pup):
Male Parent - Dd x Female Parent - Dd
M a l e
D
d
F I
Puppy One - DD
I Puppy Two - Dd
I
e D I
Double Dews
I Double Dews
I
m I
I
I
a I
Puupy Three - Dd
I Puppy Four - dd
I
l d I
Double Dews
I Single Dews
I
e I
I
I
What this tells us is that 1 in 4 pups will be "pure" (DD) for double dews, 2 in 4 pups will show the trait of double dews, but still carry a gene for singles (Dd), and 1 in 4 pups will be "pure" for single dews (dd).
If you try the punent square with each parent pure (DD) for double dews you will see that 4 in 4 pups will be "pure" for that trait, too.
If you try a punent square where one parent is "pure for doubles (DD) and one is "pure" for singles (dd) you will find that 4 in 4 pups will show the trait of doubles, but each will carry a gene for singles (Dd).
Try a square that has one parent "pure" for singles (dd) and one parent showing doubles, but carrying the gene for singles (Dd) - what is the ratio that you end up with?
Okay, I admit it, I'm a teacher! I can't stand to let a teachable moment go by! :) At any rate, I hope that helps explain the dew claw conundrum. Basically the only way to avoid single dews (if I am correct) is to only breed "pure" double dewed parents. That would take a great deal of genetic research every time a person would want to breed. Another problem might be if the genes are closely linked with the sex of the parent(s) or the puppy to show - like color blindness in humans. That complicates everything even more! Let me know if you figure out the last punent square question!
Amy, Jeff, Mischief, and Bear