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hypo question


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Posted by Paul Hollander on May 13, 2003 at 12:31:42:

In Reply to: hypo question posted by grimdog on May 13, 2003 at 08:27:54:

:The whole numbering system is whacky. A f2 boa is the result of breeding 2 salmon boas together. out of every 4 boas on average you will get 1 normal, 2 heterozygous hypos, and 1 homozygous hypo.

The numbering system is definitely whacky.

: The only true way to tell if a hypo is dominant (homozygous, having 2 hypo genes) is by breeding it to a normal, if all of the babies are hypos then you have a dominant hypo.

Change "dominant" to "homozygous" in this sentence, and it is right. "Dominant" and "homozygous" do not mean the same thing. See definitions below.

: even f4 hypos are not neccesarily dominant or super hypos. Just buy a really good looking hypo and go from there. Don't buy it because it is f4, f3, f100000000 buy it because it looks nice. Because if you breed an f3 to a normal you don't get f3s. it is just a marketing thing that is probably used improperly anyways.

Right on. An "f3" could easily be a heterozygous salmon, which is genetically equivalent to an F1.

Standard genetics definitions:

homozygous -- Chromosomes come in pairs. A gene in one chromosome is identical to the corresponding gene in the other chromosome. If we symbolize a pair of chromosomes as "//" and Sa to mean salmon, then a homozygous salmon is Sa//Sa.

heterozygous -- Chromosomes come in pairs. A gene in one chromosome is NOT identical to the corresponding gene in the other chromosome. If we symbolize a pair of chromosomes as "//" and Sa means the salmon mutant gene and Sa+ means the normal version of the gene, then a heterozygous salmon is Sa//Sa+.

A dominant mutant gene is one that causes a heterozygous individual to look like a homozygous individual. IOW, if a heterozygous salmon (Sa//Sa+) boa usually looks like a homozygous salmon (Sa//Sa) boa, then the salmon gene is dominant to the normal gene.

And to finish the triad, a recessive gene produces the mutant appearance only when homozygous. A heterozygous individual looks normal.

A codominant mutant gene is one that causes the heterozygous individual to look different from both a normal and a homozygous mutant individual. For example, a heterozygous tiger reticulated python can reliably distinguished from both a normal retic and a homozygous tiger (super tiger) retic. That makes the tiger mutant gene codominant to the normal gene.

So "heterozygous" and "homozygous" refer to whether a particular individual has one or two copies of the mutant gene.

Whether a mutant gene is dominant or codominant (or recessive) compared to the normal version of the gene depends on what the heterozygous individual looks like. A homozygous salmon apparantly cannot be reliably distinguished from a heterozygous salmon. That makes salmon a dominant gene. And salmon remains a dominant gene whether a given individual is heterozygous salmon or homozygous salmon.

Paul Hollander





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