Reptile & Amphibian Forums

I will use hypomelanism as an example but you could just as well plug in pastel, tiger, striped, piebald or jaguar. Hypomelanism is reduced black pigment. I'll assume this trait is controlled by two genes, which I'll call "a" and "b".
A = normal and is dominant
a = hypo and is recessive
B = normal and is dominant
b = hypo and is recessive

So here are all our possibilities:

Genotype Phenotype
___________________________________
AABB very dark (normal)
AABb or AaBB dark
AaBb or AAbb or aaBB medium
Aabb or aaBb light
aabb very light (hypomelanistic)

Now lets cross a heterozygous for hypomelanism with a homozygous for hypomelanism.

AaBb X aabb

First combine like terms: Aa x aa and Bb x bb. Then multiply each one out an get:
Aa Aa aa aa
Bb Bb bb bb

Then multiply each term to every other term and you come up with:
AaBb AaBb Aabb Aabb
AaBb AaBb Aabb Aabb
aaBb aaBb aabb aabb
aaBb aaBb aabb aabb

Next, combine like terms: 4AaBb 4Aabb 4aaBb 4aabb. These are the Genotypes.

And here is how they would appear, the phenotypes:
4 true hypomelanistic,
4 medium
8 light

Now just imagine what happens if the trait is controlled by 3 or more genes! That is why algebra is the prefered method to the pundit squares method. So the gene for tiger retic would just be ordinary recessive alleles controlled by two genes.

Paul Kemes

In your original adult, wouldn't it be true that AaBb would have the same color as AABb and AaBB, given that the expression is strictly dom/rec . . .
Brian

Your orignal animal
AABB very dark (normal)
AABb or AaBB dark
AaBb or AAbb or aaBB medium
Aabb or aaBb light
aabb very light (hypomelanistic)

Shouldn't it be
AABB, AABb, AaBB, AaBb (normal)
AAbb, Aabb (medium)
aaBB, aaBb (medium)
aabb (hypo)

No because Each capital letter, or dominant allele contribute directly to the degree of expression, or non-expression as the case may be. Each Dom has a cumlative aafect on the appearence.
Paul Kemes

No because Each capital letter, or dominant allele contribute directly to the degree of expression, or non-expression as the case may be. Each Dom has a cumlative aafect on the appearence.
Paul Kemes

That all depends on what A's and B's stand for. You need to get an biology or genetics book and take a look at the classic Mendel experiment with round/wrinkled and yellow/green peas. That experiment explains dom/rec taking into account 2 different systems, and the 4 possible outcomes.

I don't know a thing about jaguars or pastels, but from what "I don't know" i had heard that these were not simply dom/rec. I for some reason thought that was a dominate trait, that you only needed one of the two alleles showing, not like recessive traits like albinoism (amelanism)

Matt