There are at least nine (9) mutant genes that have been identified at five (5) different locations on the sex-chromosome of the domestic pigeon, (Columba livia).
Shown in the Gene Symbols chart are nine sex-linked gene variations, found at five different locations - (d, r, wl, St, b) - on the sex chromosome. Those with super-scripts (d, St, b) indicate they are alternatives, or alleles, at each of their respective locations.
The site of each gene's location on a chromosome is called a "locus"; and each locus can be occupied by only one gene at a time. Two genes can occupy a given location only in paired chromosomes (one on each chromosome). Also remember that all "normal genes" are considered wildtype genes (symbol = +).
In this example of an ash-red, male pigeon - dilution is found at a different location than brown and ash-red. Alleles at a given location must begin with the same letter(s). Those beginning with upper case letters indicate a dominant, and those beginning with lower case letters indicate recessive - to wildtype.
Though all wildtype genes are represented with the "+" symbol, the individual actions of each gene, which may number in the thousands - in a combined effort - produce the individual. Each of those wildtype genes are accepted as normal, or standard. Only those genes that have changed or mutated from the wildtype (called mutations) are labeled.
Note: A chromosome may have uncounted hundreds of gene locations (loci). For simplicity, only four locations are shown in the example above.
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