Posted by:
Paul Hollander
at Fri May 26 18:14:09 2006 [ Email Message ] [ Show All Posts by Paul Hollander ]
>Incomplete dominant mutations have similar phenotypes in heterozygous and homozygous forms. When an organism with the mutation is crossed with another unrelated organism the resulting offspring will show similar characteristics of both.
>
>I, like Ryan, have been taught by the flower principle. The Red X White = Pink.
I was taught by the flower principle, too. When an organism with the mutation (with white flowers, lacking pigment granules) is crossed with another unrelated organism (with red flowers, normal number of red pigment granules), the resulting offspring (the heterozygotes) will show characteristics similar to both (pink flowers, caused by fewer than normal red pigment granules). In other words, the pink flowers show similarities to BOTH homozygous forms rather than just the mutant form. This produces the third, heterozygous (pink flower) phenotype.
>Since Hypos have a variety characteristics, and I don't know of any other mutations that could be classified as incomplete dominance (other than wild type) I will use this example. Crossing two hypos with different characteristics will create offspring with components of both. Such has been done by using striped, abberant, high-color, low-speckled, broad saddled, etc.
Hmm. But aren't there striped, aberrant, etc. boas that are not hypo? That would make striped, aberrant, etc. caused by something other than the hypo mutant gene. I've checked a couple of biological dictionaries, and they said nothing about more than one locus. They were variations on this definition from www.dictionary.com: "A heterozygous condition in which both alleles at A GENE LOCUS are partially expressed, often producing an intermediate phenotype." (Emphasis mine.)
>Now this can also be classified as selective breeding, (snip)
But you can select pink flowers for a hundred years, and they will still keep producing red and white flowers as well as pink flowers. This is not what we normally think of as selective breeding.
I mentioned that wild-type boas could be labeled as incomplete dominant as well. We know that wild-type is dominant over recessive mutations, but that wild-type animals with different characteristics can be crossed for new results that are a combination factor.
It's better to call the wild type gene at each locus the standard against which each mutant is compared to determine whether the mutant is dominant, recessive, or codominant to the wild type allele.
"Wild-type animals with different characteristics" aren't all wild type animals. Many are mutants that happened to be found in the wild. Admitted that boas are variable enough in the wild that it's difficult to make a hard and fast determination of what is and what is not the wild type. 
I must logout now and won't be back until tomorrow some time. 
Paul Hollander
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RE: Okay... - Paul Hollander, Fri May 26 18:14:09 2006
