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Paul Hollander
at Sat Jul 15 18:28:06 2006 [ Email Message ] [ Show All Posts by Paul Hollander ]
>I am still trying to understand the basics of genetics? When people say het does that mean the gene is recessive?
Het is slang for "heterozygous". A gene can come in two slightly different versions. A snake that is heterozygous has a pair of genes where the two genes are not the same. One gene is the normal version, and the other gene is the mutant version. For example, a normal gene can be paired with an amelanistic mutant gene. This is the most common case. However, sometimes a gene can come in three or more slightly different versions. One is the normal version, and the other two or more are mutant versions. In corn snakes, normal, amelanistic, and ultra are slightly different versions of the same gene. A corn snake would be heterozygous if it had a normal gene paired with an amelanistic mutant gene, a normal gene paired with an ultra mutant gene, or an ultra mutant gene paired with an amelanistic mutant gene.
Some people do say that the mutant gene in a het animal is a recessive mutant gene. This incorrect view was a result of having only recessive mutant genes in snakes for many years. This has changed; in the past few years, dominant and codominant mutants have turned up in the reticulated python, boa constrictor, and ball python.
To be heterozygous, all that matters is that the two members of a gene pair are not the same. If one member of the pair is a normal gene, the other could be a dominant mutant gene, a codominant mutant gene, or a recessive mutant gene. If both members are mutant genes (but different mutant genes), then one can be a dominant, codominant, or recessive mutant gene, and the other can be a dominant, codominant, or recessive mutant gene. That gives six possible combinations of mutant genes:
1. dominant//dominant
2. dominant//codominant
3. dominant//recessive
4. codominant//codominant
5. codominant//recessive
6. recessive//recessive
Each of these is heterozygous.
A mutant gene is classed as a dominant, recessive, or codominant mutant gene depending on what an individual with the mutant gene paired with normal gene looks like. See http://reptiliandreams.com/BoaGenetics/genetics2.php
Clear as mud?
>For example If you bred 2 albino snakes all the babies would come out normal but 100% het for albino. And if the litters were bred back to each other you would get albinos? or if one of the babies was bred back to its mother you would get half albinos and half 50%het albino? Plz help as you can tell im confused?
When two albino corn snakes (usually called amelanistic corn snakes) mate, all the babies are albino (amelanistic).
In most multicellular creatures, such as corn, fruit flies, corn snakes, and humans, chromosomes come in pairs. As genes are sections of chromosomes, they also come in pairs, with one member of each pair on each of the two paired chromosomes. When sperm and eggs are formed, they wind up with only one member of each pair of chromosomes. When a sperm fertilizes an egg, the result is paired chromosomes (and paired genes) again.
I would suggest that you tear a sheet of paper into scraps. Write A on some scraps and a on other scraps. A stands for the normal version of the amelanistic mutant gene, and a stands for the amelanistic mutant gene. An adult snake has two genes, and they can be AA (homozygous normal), Aa (heterozygous amelanistic, which looks normal), or aa (homozygous amelanistic, which lacks black pigment and is what we call an amelanistic corn snake). Determine the results of the following matings:
1. AA x AA
2. AA x Aa
3. AA x aa
4. Aa x Aa
5. Aa x aa
6. aa x aa
If the first member of the mating pairs above is the male and the second is the female, determine the results if the first member is the female and the second is the male. What differences do you see between the two sets of matings?
Are there any other possible matings?
When you are doing these, remember that a baby gets two genes -- one of the father's two genes and one of the mother's two genes. If a baby gets the father's first gene, it can get either the mother's first or second gene. If a baby gets the father's second gene, it can get either the mother's first or second gene.
If you do this and write down the results, you will have a better handle on Mendelian genetics.
Paul Hollander
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RE: genetics question? - Paul Hollander, Sat Jul 15 18:28:06 2006
