What is an example of the mendelian trait in humans ?

Mendelian traits: These are the traits that are passed from parents to offspring by dominant and recessive alleles of a gene, determined by all the Laws of Inheritance proposed by Mendel.

An example of the mendelian trait in humans is Phenylketonuria:

1. It is an example of a Mendelian trait, this disorder is transmitted from parents to the offspring when both parents are heterozygous (Aa) and both are homozygous (aa) conditions.
2. The autosomal recessive inherited disorder is caused by the lack of an enzyme that converts amino acid phenylalanine into tyrosine, as a result, the amino acid gets accumulated and converted into toxic form phenyl pyruvic acid, which gets accumulated in the brain of the affected person which results in mental retardation.