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Genetics Primer |
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| Terms | Basics | Dominance | Appearances | Calculations |
Appearances
In the real world guppy genetics is very complex and in some strains is still not fully understood, so if you are having problems with a strain take heart! Even the pros don't fully understand guppies!
We began our study by looking at albinism. In guppies, as in many fish, albinism is incomplete. This means that not all melanins (pigment, if you will) are suppressed, only those for black and brown are masked.
There are two more terms that will be useful now. They are phenotype and genotype. A phenotype describes the physical appearance (e.g. albino or full color), while the genotype describes the genetic structure (e.g. CC, Cc or cc). It's easy to remember which means what if you remember that "PH" goes with PHenotype and PHysical, and that "GEN" goes with GENotype and GENes.
If we mate a homozygous full color guppy (phenotype=full color, genotype=CC) with a homozygous albino (phenotype=albino, genotype=cc), we will come up with all heterozygous full color guppies (phenotype=full color, genotype=Cc). If we mate two of these offspring (CcxCc) we will get offspring with two different phenotypes and three different genotypes. 25% will be CC (phenotype=full color, genotype CC), 50% will be Cc (phenotype=full color, genotype=Cc) and 25% will be cc (phenotype=albino, genotype=cc).
The point to be made here is that phenotype and genotype are not the same. You can mate two fish with identical phenotypes and genotypes (appearances and genetic codes) and create fish with very different phenotypes and genotypes. This is what makes genetic breeding possible.
We have been making statements similar to "breeding two Cc guppies will result in 25% CC, 50% Cc and 25% cc" throughout this primer, but it cannot be stressed enough that this is just an expectation of an average outcome. Yes, 25% should be CC, but there is no guarantee that this will take place. A gambler rolling a die should get a "6" one out of every six times he rolls, but this almost never takes place in reality. He could also roll a "6" five times in a row. Genetics are just as random.
Rarely will a mating of two Cc guppies ever yield exactly 25% CC, 50% Cc and 25% cc. A mating resulting in 100% CC is quite possible. For that reason, results of one mating should never be trusted. Only over the long run with multiple matings can we begin to tell anything with certainty.
One other thing on commonly accepted standards for recording your genetic findings before we move on. If we know exactly what a pair of genes are (e.g. the genotype for an albino guppy is always cc), we can be safe in putting "cc" down on paper. If we are not sure what a gene pair is (e.g. the genotype for a full color guppy could be CC or Cc) it is customary to record the genotype with a dash "-" in place of the uncertain gene. For example, if we were not sure if a full color guppy had a genotype of CC or Cc we would describe it as "C-" instead of CC or Cc.
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