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Home > Genetics Study > Terminology of genetics
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|Terminology of genetics |
By: Joep van Esch
One thing that is really important with genetics is to understand the terminology used. I will try here to clarify some of the basics which are indispensable in betta genetics [1,2,3].
DNA: Deoxyribonucleic acid, the heritable material of an organism.
Gene: The units of inheritance that transmit information from parents to offspring.
Chromosomes: A long threadlike association of genes in the nucleus of all eukaryotic cells which are visible during meiosis and mitosis. A chromosome consists out of DNA and proteins. An organism always has 2n chromosomes, which means that all chromosomes are paired.
Genotype: This is the genetic makeup of an organism: the genes
Phenotype: The physical and physiological traits of an organism. These are influenced by genetic makeup (genes) and surrounding.
Allele: Another word for gene. Each chromosome has a copy of this allel, thus a gene-pair.
Homozygous: This term indicates that an organism has two identical alleles at a single place on a chromosome. This results in an organism that breeds true for only one trait.
Heterozygous: This term indicates that an organism has two different copies of a gene on each chromosome.
Dominant gene: In a heterozygote, this allele (gene) is fully expressed in the phenotype. In genetic schemes, these genes are always depicted with a capital letter.
Recessive gene: In a heterozygote, this allele (gene) is completely masked in the phenotype. In genetic schemes, these genes are always depicted with a lower case letter.
Intermediar gene: This is when in a heterozygote, an allele (gene) is not fully masked in the phenotype. You can already see some of the characteristics of the gene. A good example is the dt-gene (see tail type definitions & genetics).
I think I now covered the basics….. now an example to visualize this using the allel for hair color in humans:
Brown hair is a dominant trait. How is it possible that two parents with brown hair get a blond daughter of son?
The allel for "brown hair" is dominant and depicted with "B".
The allel for "blond hair" is recessive and depicted with "b".
The answer lies here: Remember that all alleles come in pairs and that the parents have to be heterozygous for the allel for haircolor. This means that both parents have to posses the recessive trait for blond hair ("b") besides the dominant trait for brown hair ("B"), thus "Bb". The best thing to visualize this is by the use of a Punnet-square:
Summary: The offspring of two parents carrying the heterozygous "Bb" genotype can result in the following offspring: 25% homozygous for brown hair ("BB"), 50% heterozygous for brown hair ("Bb") and 25% homozygous for blond hair ("bb")
Then some basic rules about genetic crosses.
When two unrelated parents are crossed their hybrid offspring are called the F1 generation (for the first filial generation).
When the F1 offspring is interbred their offspring will be called the F2 generation (for the second filial generation).
When the F2 offspring is interbred their offspring will be called the F3 generation (for the third filial generation). And so on........
This interbreeding of offspring can be done up to F8, but one has to check the offspring very carefully each generation on abnormalities. So it is advisable to use an out-cross (unrelated partner, fresh blood) once in a while.
When one of these offspring (doesn't matter of which generation) is crossed with an unrelated partner, their offspring is again F1.
1. Campbell, N.A., "Biology", Fourth edition, The Benjamin/Cummings Publishing Company, Inc., ISBN 0-8053-1940-9
2. Zakwoordenboek der Geneeskunde, 25ste geheel herziene druk, Elsevier/Koninklijke PBNA, ISBN 90-6228-255-5
3. Betta Bunnies genetic page, http://www.geocities.com/Petsburgh/Farm/5592/genetics.html
Source: Betta Territory
|Category: Genetics Study|
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HEJSAN FROM SWEDEN EVERYONE! Everything in Sweden is going well, although I'm still busy learning the language and coping with a newborn, so it will be a bit before I'm as active as I'd like with the fish. This is a Facebook update! I have created a new BettySplendens Facebook page that will be used exclusively for betta-related networking. On the 16th of August I will be going through and deleting most of the people on my personal Facebook page who are not actual friends or family (many of you have become friends through the course of the hobby, and of course will not be deleted). If for any reason you wish to remain on my personal page, please let me know by emailing email@example.com, or FB email. Otherwise, go to the new BettySplendens Facebook page and click the 'like' button for more betta-related news and updates :).
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Slight change of plans! I have decided that, instead of reinventing the wheel, I'm going to create a personal FB page and use the old one purely for betta stuff. So if you're on the original page (now called BettySplendens Bettas), please stay put! :P
For all the betta inquiries:
Just a reminder, I am not selling bettas in the US at the present time. I may begin to supply a few select bettas throughout Europe sometime in late Spring 2011. Cheers!
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