Information Available from the F₁ and F₁ reciprocal progeny. 

By looking at the phenotypes of the F₁ and F₁ reciprocal crosses  you can determine:

 (a) whether the traits are dominant, incompletely dominant, overdominant, codominant,  or recessive and 

  (b) whether the traits  are autosomal or sex-linked. 

Dominant or Recessive::  To determine whether a trait is dominant or not, you must have an organism that is known to be heterozygous. The parental phenotype that occurs in a heterozygous organism is dominant. The parental phenotype that reappears in the F₂ is recessive. The only organism that must always be heterozygous when you do not know if a gene is autosomal or sex-linked is the F₁ female. The phenotype that you see in the F₁ female is the dominant phenotype.

Autosomal or Sex-linked: To determine whether a trait is autosomal or sex-linked you must look at the males from the F₁ and the reciprocal F₁ crosses.  If a trait is sex-linked (on the X-chromosome), then the males from the F₁ crosses will always have the phenotype of their homozyous mothers. Consequently, the results of the reciprocal F₁ crosses will be different.  Males may or may not resemble their sisters depending on dominance. If the males from the reciprocal F₁ crosses look the same and they look like their sisters, then the trait is autosomal.

These are the F₁ patterns that you can expect to see for the four crosses:  In all cases we are testing an unknown mutant phenotype vs a wildtype phenotype.