explain why "pleitropy" is the rule,rather than the exception,for phenotypic expressions of genotypes.

Answer 1

Pleiotropy is when a single gene affects multiple traits. The expression of traits is rarely associated with a single gene, the mendelian genetics examples you work on are by far the exception rather than the rule. Most often, the expression of a trait is associated with a whole cascade of genes, that work in pathways or networks. Many pathways interact, so single genes are often related to multiple traits.