The gene disorder phenylketonuria is an example of

$A$ single gene can exhibit multiple phenotypic expressions; this is called.....

In pea plant,the genotype $(BB)$ shows:

In humans,the gene responsible for Phenylketonuria produces multiple phenotypic expressions,collectively known as a syndrome. This gene causes mental retardation,broad incisor teeth,skin pigmentation,and excessive sweating. What is this type of gene called?

Find the correct statement.
$(1)$ Generally a gene regulates a trait,but sometimes one gene has an effect on multiple traits.
$(2)$ The trait $AB$-blood group of man is regulated by one dominant allele and another recessive allele. Hence it is co-dominant.

Genes exhibiting multiple effects are known as