As a student of genetics, I notice this incorrect usage of terminology... all the time in ha-rpg. And to be honest, it drives me a little batty, so I figured, why not post a journal to point out correct terminology and basically stop ranting in my head?
Gene: A DNA sequence that codes for a protein.
Allele: Two or more variations of a gene.
Dominant: A gene that only needs one allele to be expressed
Recessive: A gene that needs two/all alleles to be expressed
Heterozygous: All/some alleles are different
Homozygous: All alleles are the same/similar
Alleles are part of genes, but genes are not part of alleles. Using 'gene' to describe an allele is easy to mistake, but it is wrong.
A gene is a whole, alleles are part of the whole and what make up the coding of the gene an organism has. Each gene has two alleles, that may or may not be the same, depending on inheritance. They make up how the gene is expressed in the individual and may or may not surpress the expression of other genes. Confused yet?
Let me first point out that Dominant and Recessive do NOT refer to Alleles. They refer to the expression of the gene itself. It is easy to get confused, as some journals and documents use dominant and recessive in conjunction with heterozygous and homozygous to explain both the expression of the gene and the number of same alleles(In horses, diploid, or two.)
A dominant gene would be silver. Why? Because you only need one copy of silver to be expressed on the horse. HOWEVER, a horse with only one copy of silver is NOT referred to as recessive. Why? Because whether or not they have a silver offspring, they still have the chance of producing a silver without needing another copy of silver from the other parent. A horse with one copy of silver is referred to as heterozygous for silver.
A recessive gene is flaxen. Why? You need two copies of the flaxen gene to have flaxen expression. Therefore, any horse that has flaxen expression would be considered homozygous for flaxen. NOT recessive, NOT dominant. It carries a recessive gene, but it has both copies of it. Makes sense? Any foal it has will NOT express flaxen, unless a flaxen is given from the other parent.
However, that foal can foal a flaxen, if bred to another flaxen carrier. Both of these carriers would be considered Heterozygous, because they have one flaxen allele, and one non flaxen allele.
Genotype: Ee/aa/Lplp/Toto - Black pintaloosa
Allele: E and e -Heterozygous
Lp and lp - heterozygous
To and to - heterozygous
Overall, this horse is heterozygous for everything. (aa is not counted because it does not affect anything.) It is not dominant or recessive for anything as all these genes are co-dominant.
Genotype: ee/AA/ff - Flaxen Chestnut
Allele: ee- homozygous
AA - Homozygous
This horse is homozygous for everything. This is where it gets tricky. ff is the recessive gene that needs two copies to work, so many people will call it homozygous recessive. This is still not referring to the allele, f, but to the whole, ff. It is recessive because if a F is thrown in there, it changes the expression.
BUT, you can't just drop the homozygous and call this horse a recessive. Because it is not. Each allele it has, because it's homozygous, it will give to the next offspring and some phenotype will be shown. The only thing truely recessive about this horse is that it carries the recessive gene, flaxen. Therefore, this horse is homozygous for all genes and expressing the recessive gene, flaxen.
Toto -not recessive, heterozygous
Znzn - not recessive, heterzygous
EE - not dominant, homozygous
LPLP - not dominant, homozygous.
Most horse colour genes are NOT dominant, because they coexist with other genes and modify the expressions. At most, they will be referred to as epistatic dominant genes, which basically means that it has varied expressions that cannot really be predicted, such as overo and tobiano and only need one allele to be expressed.
Therefore, your DOM mutation nordies... are not DOM at all. They are Homozygous.
Want more information on how genes and alleles work? Check this in depth explanation out.harpg-newsletter.deviantart.co…
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