Final answer:
The phenotype of an organism, including the expression of pair rule genes, is determined by the interaction between its genotype and environmental factors. Mendel's experiments illustrate the difference between genotype and phenotype, revealing that some traits may not be expressed in the phenotype but are carried genetically. Epistasis can further affect phenotypic expression by having one gene influence the expression of another.
Step-by-step explanation:
Phenotype and pair rule genes determine the observable characteristics and patterns of segmentation during embryonic development in organisms. Phenotype is the composite of an organism's observable characteristics or traits, such as its morphology, development, biochemical or physiological properties, and behavior. These characteristics are determined by the organism's genotype, the set of genes it carries, and the environmental influences it experiences. Pair rule genes are a set of genes that work together to establish the segmented body plan of an organism early in embryonic development.
Mendel's hybridization experiments provide classic examples to distinguish between genotype and phenotype. When true-breeding pea plants with different seed colors were cross-breeding, the resulting F1 hybrid offspring displayed the dominant seed color, demonstrating the phenotypic expression. However, since the recessive seed color reappeared in the F2 generation, it showed the underlying genotypic variation within the hybrid plants, which is not always observable in the phenotype. This concept is crucial in understanding genetic inheritance and expression.
Epistasis is another significant genetic factor that can alter phenotypic expression. It occurs when the expression of one gene is masked or altered by another gene. For example, in certain cases of coat color in animals, the presence of one allele can entirely mask the expression of another gene, resulting in varying phenotypes even among individuals with the same genotype.