A Detailed Article: Comparison of the Pastel-face mutation: heterozygotes vs. homozygotes:

A Detailed Article of Comparison of the Pastel-face mutation: heterozygotes vs. homozygotes:

It is important to note that the Pastel-face mutation is recessive; therefore, it requires input from both the father and the mother to manifest in the bird—either through carriers (genotype) or birds with the visible Pastel phenotype. This means both parents must either possess the trait or carry the gene to produce a bird with the Pastel phenotype.
Regarding the Pastel mutation, we must distinguish between heterozygotes (impure Pastels mixed with White-face) and pure, or homozygous, Pastels.
The Pastel-face mutation shares a gene with the White-face mutation; consequently, the Pastel trait always prevails over the White-face trait in pure Pastels. If we cross a White-face with a pure Pastel, the offspring will always be Pastels, but they will be heterozygous (impure).
A key characteristic of the impure Pastel is that it can produce both White-face and Pastel-face offspring, whereas the pure Pastel cannot. As mentioned, since the Pastel mutation shares a gene with the White-face mutation but is dominant over it, the Pastel mutation is effectively “stronger.” When pairing two heterozygous (impure) Pastels, the offspring include pure Pastels, impure Pastels, and White-faces. When pairing an impure Pastel with a pure one, the offspring will always be Pastels. It is worth noting that when a White-face is produced from two heterozygous Pastels, that White-face will never carry the Pastel gene—the White-face mutation cannot carry the Pastel mutation. Conversely, while a heterozygous Pastel can produce White-faces, a pure (homozygous) Pastel will never carry the White-face trait.
Heterozygotes and homozygotes are easy to distinguish; let us look at a photographic comparison.
It is easy to see that some heterozygous specimens have a white border around their facial mask—a trait some attribute to White-face influence—whereas this detail is absent in homozygous Pastels. The yellow coloration is much more beautiful and striking in the pure (homozygous) bird than in the impure (heterozygous) one. It should be noted that the Cream Face mutation acts in the same way as Pastel Face, sharing a gene with White Face; however, Cream Face and Pastel Face do not share a gene with each other. Cream Face also presents in both heterozygous and homozygous forms. Aviary Nazarí
Team Nazarí by Rob García Hernández
Country spain , Granada