Genetics question -

[Seneschal]

No, if it were dominant and the parent carrier was heterozygous spider (visible spider) bred to a normal then the spider parent would only contribute one allele, not necessarily the one necessary for a spider morph.

---S---N
N| SN NN
N| SN NN

so, 50% spider, %50 normal.

---S---N
S| SS SN
N| SN NN
50% heterozygous (but still visible spider), 25% normal, and 25% homozygous spider--theoretically identical to the het spiders, so you wouldn't be able to tell unless you bred it to a normal.

---S---S
N| SN SN
N| SN SN

so the homo spider bred to a normal would make all spiders, thus theoretically proving the spider a dominant gene and proving that particular spider parent to be homozygous for the trait.

[littleindiangirl]

Right, your 50/50 is still what most would call the co-dom morph because the het version expresses that gene, just like pastel and many others. I'm more interested in what actually comes from a spider/spider crossing for 2 consecutive generations. If there is actually a homozygous form.

[Seneschal]

As a dominant gene the homozygous form of the animal would be identical to the heterozygous form.

[Seneschal]

Here's a visual representation (the pics aren't mine but there you have it.)

DOMINANT GENES: Spider used as example.




CODOMINANT GENES: Pastel used as example.

[Morphie]

So based on my admittedly rudimentary observations, it would appear that Spider is indeed a one-gene-two-allele-deal where the spider gene is dominant - so it would be interesting to learn if "spinning" spiders are more often homozygous than they are heterozygous, or vice versa (which would be a good argument for sequencing).

Further, the Pastel gene appears to be a case of "incomplete dominance" (as opposed to co-dominance), where the gene for Normal and the gene for Pastel compete to produce a "mixture" or your standard pastel. The pastel gene un-hindered by the normal gene makes your super-pastel.

In the case of the Mojave, Co-dominance would perhaps be more likely since the heterozygous form (the mojave) does not at first glance appear to be a "mixture" of a normal and a leucistic.

If anyone has an argument, please speak up.