Genetic Notation
There are three kinds of notation commonly used by geneticists. These are sometimes referred to as plant notation, animal notation and bacterial notation since they were originally developed by botanists, zoologists and bacteriologists. These are not limited as their names would imply however. Early human geneticists used plant style notation as do many writers of elementary genetics texts. Current corn and tomato geneticists use animal style notation, often modified by bacteriological style. So you may see any of the styles, "regular" or modified, in any of the kingdoms. The basic rules are set out below.
Plant style notation
The basic concept needed here is dominance & recessiveness. (Only works well if there are only two alleles per gene and if one allele is expressed in the phenotype and the other isn’t.)
1. Pick a letter or letters that refers to the recessive phenotype, the general characteristic or the dominant phenotype.
Let’s say you were observing purple flowers and white flowers in peas. Possible choices would be a letter that refers to white (recessive), to purple (dominant) or to color.
2. Make the recessive allele lower case and the dominant allele upper case of the same letter.
For example
W = purple, w = white is OK. C = purple, c = white is OK. P = purple, p = white is OK.
However, P = purple, w = white is NOT OK [same letter must be used]. Also, p = purple, P = white is not OK [dominant must be upper case].
Animal style notation
This notation is based on the concept of "wild type". The wild type is the most common phenotype in the population.
1. Pick a letter (or group of letters) that refers to the non-wild phenotype or the general characteristic.
2. If the non-wild allele is recessive, use a lower case letter to symbolize it. If non wild is dominant, pick an upper case letter to symbolize it.
3. The wild type allele is the same symbol as the non-wild with a + superscript.
4. If there are more than two alleles, letter superscripts are used with lower case superscripts usually meaning the allele is recessive to the initial dominant and upper case superscripts if the allele is dominant to the initial dominant.
For example, color is wild and dominant, albino (white, no color) is recessive and non-wild.
a = albino, a+ = normal color is OK. c = albino, c+ = normal color is OK. w = albino,
w+ = normal color is OK.
However, a = albino A+ = normal color is not OK [both letters must be the same]. Also
w = albino, b+ = normal color is not OK [don’t mix letters].
For another example, Achondroplasia (a form of dwarfism) is non-wild and dominant, normal height is wild and recessive.
A = achondroplastic, A+ = normal height is OK. D = achondroplastic (dwarf), D+ = normal height is also OK. H = achondroplastic, H+ = normal height is acceptable.
However, A = Achondroplastic, N (or N+ or n+) = normal are unacceptable [no mixing letters, both letters must be upper or lowercase].
For another example, agouti is wild and dominant, solid (non-agouti) is non-wild recessive and Yellow is another allele which is non-wild dominant.
a = non-agouti, a+ = agouti, aY = yellow is OK [In some texts, yellow is incorrectly written as AY.]
Microbial style notation
Since bacteria are haploid, dominance and recessiveness do not matter. Notation depends on what the protein coded by the gene or the gene itself actually does.
1. Pick a letter or group of letters that describes the gene or what it does
2. put a + superscript if the gene (or protein coded) works. Put a - superscript if the gene (or protein coded) doesn’t work. (Other superscripts can be used to describe other phenomena—superscript c to designate regulatory genes that cannot turn off the genes they regulate, etc.)
cysA+ = can make the protein coded by cysA, cysA- cannot make the protein coded.
laci+ = normal regulatory gene, lacic = regulatory gene cannot turn off the genes to make lactose degrading enzymes.
Problems
1. In peas, flowers can be either terminal (recessive) or axial (dominant). How might you symbolize the alleles involved?
2. In mammals, color can be either full (dominant) or diluted (recessive). If full color is wild, how do you symbolize the alleles?
3. In humans, normal eyelids are recessive to ptosis (drooping eyelids). How do you symbolize the alleles?
4. If Wr is round and wr is wrinkled, what is the phenotype of the heterozygote?
5. If W is albinoid (white) and W+ is normal, what is the phenotype of the heterozygote?
