As mentioned earlier, all the chromosomes in male birds (pigeons) are paired.  In females all chromosome are paired except one.  A new embryo having all paired, or an even number, of chromosomes will develop into a male.  When it has an uneven (one chromosome unpaired) number of chromosomes it will develop into a female.

The following chart deals only with the chromosome that determines the sex of the bird, i.e., the sex-chromosome.  The classic pairing of a wildtype male and an ash-red female is used to explain how, in some cases - the sex of the offspring can be determined by the color of their plumage - at two to three weeks of age.   The dominant, mutant, ash-red gene is located on the sex chromosome.  (It may be useful to review this example to better understand  dominance and recessiveness of a mutant gene.)

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