Codomince = Both alleles expressed distinctly together (e.g., Roan cattle coat with distinct red and white hairs, ABO blood group $I^A I^B$).
Incomplete Domince = Blended intermediate phenotype (e.g., Red $\times$ White = Pink flowers in *Spdragon*).
Step 1: Understanding the Question:
The question asks to categorize the genetic inheritance pattern responsible for roan coat color determition in cattle. Step 2: Key Formula or Approach:
In Mendelian inheritance, complete domince allows one allele to mask another. In non-Mendelian inheritance:
• Incomplete Domince: Heterozygote displays an intermediate, blended phenotype.
• Codomince: Both alleles in a heterozygote are fully and simultaneously expressed without blending. Step 3: Detailed Explation:
• Genetics of Cattle Coat Color: In cattle (such as Shorthorn breeds), coat color is controlled by an autosomal gene with two main alleles: $R^R$ (red coat) and $R^W$ (white coat).
• Homozygous Genotypes: $R^R R^R$ cattle express red pigment throughout their coat, while $R^W R^W$ cattle express white coats.
• Heterozygous Genotype ($R^R R^W$): Heterozygous cattle display a "roan" phenotype. A roan coat consists of individual red hairs and individual white hairs interspersed together across the animal's body.
• Why Codomince? Because both the red allele and the white allele are expressed fully and distinctly side-by-side in the same organism without blending into pink, this serves as a textbook example of codomince. Step 4: Fil Answer:
The coat color in cattle (roan coat) is a classic biological demonstration of codomince.
